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Practical Wiring - Professional Motorsport: Step 2 - Layout, Branching and Routing Design

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Step 2 - Layout, Branching and Routing Design

23.26

00:00 - The second step of the HPA 10 step motorsport harness construction process is that of determining how the harness will physically route through the vehicle and the engine bay.
00:10 With the first step of the process completed we have a design for how all the components will be electrically connected but we ned to determine how the harness will physically connect to all the parts of the EFI system.
00:21 When dealing with a professional motorsport vehicle, the use of sub harnesses is much more prevalent as opposed to a modified street car or a club day track car, as often items need to be changed quickly in the pits and being able to disconnect a sub harness from the main harness and remove that section of wiring intact with the component can be a real time saver.
00:42 If the components and connectors on an item are in a tricky to get to place, using a sub harness to consolidate those connectors and bring them out to a more easily reachable location is a real help.
00:53 I have mentioned previously that it's important that all the component parts of the EFI system are installed before we begin designing our wiring harness, as we need to know where they are in order to wire to them.
01:04 In the real world however, budget and time constraints usually mean that we need to begin building the harness before all the pieces of the puzzle are in place.
01:13 This is also where sub harnesses can be extremely useful.
01:17 You can install a connector on the harness which contains all of the wires needed to make a connection to those missing components and shift that part of the build process downstream.
01:28 We can get on with the design and build of the main harness, worrying about the sub harness later in the process even considering it as its own complete harness construction project.
01:38 When we're deciding how to route the harness, there are three main elements we want to keep at the forefront of our minds.
01:44 Movement, heat, and interference.
01:46 By movement I mean keeping in mind how parts of the harness will need to move when the vehicle operates.
01:53 When being driven hard, an engine on isolated mounts will move around quite a lot as it accelerates and decelerates suddenly.
02:00 If our wiring harness is attached to the vehicle body and also to the engine, there will need to be slack between these two points to allow for this movement.
02:08 This is not just for engines, the same can be said for any drive line component, which is not rigidly mounted.
02:14 Suspension members are a good example of this, as often we will be measuring vehicle parameters like wheel speed and brake temperature out at the hub.
02:22 The wiring harness will need to be able to move with the suspension as it goes through its complete range of travel and ensure that it never binds up.
02:29 Another sort of movement we need to consider is vibration.
02:32 Racing engine vibrate like nothing else, and often are solidly mounted to the vehicle chassis, causing those vibrations to travel through the vehicle also.
02:42 Wiring can really suffer if it's subjected to strong vibrations over a long period, suffering either internal failures or failures from abrasion and chaffing.
02:52 To alleviate this, using some isolation material in your harness mounts is a good idea.
02:58 If you're using P clips for example to secure your harness, use rubber isolated ones.
03:03 A good example of this can be seen with an oil pressure sensor on a professional race engine.
03:08 It will most likely not be mounted directly into a pressure port on the engine, but instead be secured a rubber isolated mount and have a small flexible hose run to it from the engine's pressure port.
03:20 Avoiding heat with our wiring harness should be fairly common sense.
03:24 Exhaust systems are the main source of heat we'll be dealing with and the best course of action is simply avoidance.
03:31 You want to keep your wiring harness routed as far away as possible from the exhaust system or any other sources of heat whenever possible.
03:39 Wiring that does need to travel near the exhaust such as exhaust gas thermocouple wiring and O2 sensor wiring, will have a higher heat rating and usually have a heat protection sleeve or coating in place.
03:51 Even so, it's best practice to get this wiring away from the heat source as quickly as possible.
03:57 In particular I find the wiring on a Bosch LSU 4.9 wideband O2 sensor to be susceptible to heat and I always strive to find a way to get this wiring away from the exhaust system in as short of a run as possible.
04:10 Fabricated heat shields can also be a real help.
04:13 In particular where a connector needs to be mounted.
04:16 If a mount for the connector body can be fabricated, that also protects it from heat, this is great as it obeys one of the key rules of motorsport vehicle construction which is getting a single component to do more than one job whenever possible.
04:30 When we're routing our harness it's best to try and imagine the engine as it will be when it is running in the car out on the street or the racetrack.
04:37 This will help you avoid any possible interference issues.
04:41 There are items on the engine that will move in relation to the engine.
04:44 In particular the front pulleys are items that we need to pay a lot of attention to.
04:49 A piece of wiring harness caught up in a pulley will make a mess very quickly.
04:52 And this needs to be considered carefully as often we'll be wiring near to these items as they're where we're getting the engine speed and position information from.
05:02 Care must be taken to secure the wiring harness out of the way of external rotating engine components.
05:08 Once again, rubber isolator p clips can be great for this as there's usually a bolt hole location that we can pick up on to mount the harness out of harm's way.
05:17 Often it's as simple as using cable ties to secure the harness in a particular way but you need to be careful when doing so and document the need to do so.
05:26 As if the wiring harness is ever being installed by somebody else and they're not aware of the need for those cable ties, disaster could result.
05:34 Those are the three key elements you should be considering when deciding how to route the harness through the vehicle you're working on.
05:41 However aesthetics absolutely play a part also.
05:44 And there's an engineering saying that if something looks right, it probably is right.
05:48 And by this I mean that if your harness looks like a rats nest in the vehicle, it's not going to inspire confidence and most likely be much harder to troubleshoot if there are any issues.
05:59 Nice straight harness sections that are run in line with other components will always look great and often make the harness easier to secure in place as well.
06:08 A tidily constructed logically branched wiring harness run through an engine bay can become a bit of a show piece.
06:15 And as long as there isn't a huge weight or cost disadvantage, don't be afraid of running your harness in such a way as to make it a feature of the vehicle.
06:23 Out here at the engine bay of the RX7, we're gonna get stuck in to designing our routing layout.
06:29 Now this is very much the same process as we've gone through at the club level course.
06:32 I'm going to use my trusty nylon rope here to build a mock up of the harness as I would like it to run through the engine bay.
06:40 I did mention earlier on that it's really common in the motorsport and the performance automotive world in general to be dealing with those budget and time constraints that mean all the pieces of the puzzle might not yet be here, and that is absolutely the case with the RX7 here.
06:55 We've actually got a completely new fuel system on the way, new fuel rails, and injectors and that is going to move the position of those injector connectors.
07:03 Totally different injectors as well.
07:06 We've also got a cast turbo stainless manifold on the way, that we're going to be fitting a BorgWarner 8374 turbo to.
07:13 So ditching the twins and moving to a single there.
07:16 Additional to that we are looking at some future upgrades for this vehicle.
07:19 Currently we're going to be keeping the stock lower and upper intake manifolds and the stock throttle body assembly.
07:26 The throttle body assembly on the FD RX7 is actually reasonably complicated.
07:29 It's got three throttle blades, just to get around some of the air flow issues that rotaries tend to have in the low to mid RPM range.
07:37 We're gonna be keeping that set up to begin with.
07:40 But eventually we do want to move to an e throttle set up.
07:42 So to make that possible down the line I am going to be breaking out all the throttle wiring so it's going to be the TPS signals at the moment.
07:49 But also a secondary TPS signal and an H bridge driver signal into an Autosport connector so we can easily build a small sub harness to fit an e throttle at a later date.
08:02 We're also upgrading the ignition coils on the car here, moving to a single coil per spark plug.
08:08 IGN1A setup that's going to be mounted here on the top of the engine.
08:13 So those aren't yet mounted so we're going to be using a sub harness there as well in a logical location so we'll be able to build the mount and then build the sub harness for those coils.
08:23 Going to get started threading my rope through the engine bay here.
08:27 The first point I want to consider is going to be where are we going to enter the engine bay, as we are still installing our ECU and our power supply system in the interior of the vehicle.
08:38 Now we're going to be making the pass through from the interior of the vehicle to the engine bay using some Autosport bulkhead connectors.
08:44 So we need to think about where we're going to position those.
08:47 In this instance and probably for most race cars that are going to be based on a road car chassis, you'll want to reuse the original location where the OEM loom passed through into the engine bay.
08:59 It's an existing hole that gets you in the place you need to be without having to make any more cuts into the vehicle.
09:06 That's exactly what we're going to do here.
09:07 It's just down below our ABS pump and it should be large enough that we can build a plate to mount on there that we can put our two Autosport bulkhead connectors on, that's going to get our connection into the engine bay harness.
09:19 I'm going to start threading our rope through in the engine bay here and I'm actually going to start from our bulkhead connection point and I'm gonna thread it down next to where that's going to be and just get it situated as I'm gonna want the harness to run.
09:32 In this instance it's going to be best to head underneath our air conditioning lines here and actually underneath our heater lines as well as that's gonna get us nice straight shot in line with that bulkhead connector position and we're going to have right angled boots on those to bring that wiring straight out from the bulkhead connector and head off in the correct direction.
09:53 So I'm just gonna get this on the right side of those fuel lines there, as chances are these will actually be moving with our new fuel system as well.
10:02 And just start pulling this through into the engine bay.
10:04 Now what I'm doing here is I'm gonna pull this through and actually pull through a reasonable amount of length as it's a wee bit tricky to feed it through positions like this, so if you can get that done early on it's best to.
10:17 So I'm gonna feed through a good amount of length and get this positioned as I think I might like it to run on the engine and then we're gonna refine it from that point.
10:26 What I'm really doing here is I'm mapping out the longest run that our harness is going to take.
10:30 So that's going to be from our bulkhead connector point here, across the engine to our furthest most sensor.
10:36 And in our instance, that's going to be our engine position sensors on the front of the motor here and actually also our knock sensor here as well.
10:44 So because those are all reasonably equidistant, I'm going to probably make a branch point in the harness around about here where the harness will branch out and head to those individual sensors.
10:55 So I've actually threaded through a little bit too much rope here so I'm just gonna reverse that a wee bit and just avoid wasting cutting that rope and having a bare section so we'll just get this back into place.
11:10 Now things I'm thinking about when I am deciding on this route are the things we talked about at the beginning of this section.
11:17 We're looking at avoiding any sources of heat.
11:19 I'm going to keep a bit of slack in the harness at this point because that's going to be the bridge between the motor and the vehicle body.
11:28 And I'm making sure that I'm going to be keeping the harness away from our pulleys on the front of the engine here.
11:35 Other things I'm looking for when I'm deciding upon this route are the availability of good threaded locations on the engine for securing the harness to the engine.
11:45 On the top of the rotary housings here we've got a couple of threaded bosses which are used for mounting the original coils to.
11:52 Now we are going to be mounting our upgraded coil setup in the same spot, however there is going to be room for the harness to pass through here, so we'll be able to get a p clip onto it and get it supported at this end.
12:04 At the back of the harness here, chances are I would pick up off one of these points on the gearbox and once again just another p clip to keep that harness supported.
12:14 Now for that branch point, at the end of the harness here, we're in a pretty good situation as far as getting our lengths correct.
12:23 In that we're going to be using the original engine position sensors but we are potting them and breaking them out to flying leads.
12:31 So that means that I can actually situate the connectors on the harness in a range here, it's not going to have to be exact, and then when we come to the final install, I'm going to trim the pigtail on the engine position sensors to actually match the harness and terminate to the connector.
12:49 That's going to be quite a lot easier to get a really really tidy fit.
12:52 We'll start determining the points that the main harness route is going to branch out now to reach all the different components it's going to need to.
12:58 First one I'm going to consider is our engine coolant temperature sensor, right here.
13:03 They are actually pretty good, the factory engine coolant temperature sensor's quite reliable.
13:07 That's a brand new one in there and sealed with a new washer as well, so we're gonna end up reusing that.
13:12 So I'm simply going to branch out our harness at a nice logical point, and head to that engine coolant temperature sensor.
13:19 Now determining that branch point, there's a couple of other things I want to think about there.
13:24 Which is determining if there's any other harness sections that we could also branch out of that point to limit the number of overall branch points we're putting in our harness.
13:35 They are definitely the most complicated and time consuming part of the process, so if we can limit their number, it is going to be much better.
13:42 Now as I've mentioned, we're going to have quite a few sub harnesses on this setup.
13:46 So we are going to have the connectors for those breaking out from the main harness.
13:51 Really good thing about sub harnesses is that you're often quite free with where you can place the connection point for them.
13:58 And having that flexibility can help you to get a really nice tidy result.
14:02 In this instance along with considering the engine coolant temperature sensor, I'm going to branch out the sub harness connector for our ignition coils and our injectors from the same spot as well.
14:15 And that's just going to make the overall construction process much easier.
14:18 So for that reason, I'm going to put the branch point slightly further back than might seem logical for our engine coolant temperature sensor here.
14:28 And we're going to end up with a couple of harness sections running right next to each other but that's totally OK, you can cable tie those together and they will still look really tidy.
14:37 So I've mentioned we've got a couple of our sub harness connection branches that are going to be coming out of that same branch point.
14:44 Need to make a decision about where they're gonna branch out and how long those harness sections are going to be.
14:51 Now on top of the centre rotor iron here we've actually got quite a nice threaded boss and I think I'd like to pick up off that.
14:58 Possibly make a right angled bracket and that can hold the flanged autosport connectors which are gonna connect to the sub harnesses of both our injector sub harness and our ignition coil sub harness as they're both gonna be mounted in this area.
15:13 With another bit of rope here, I'm going to get those lengths on there and while I'm doing this I'm being careful to make sure that I tape these pieces of rope to the branch point in the orientation that they're going to need to be as they exit that branch point and then we're going to use that and document it when we generate our documentation and build to that design, and that's gonna ensure that everything will fit really nicely.
15:56 That should actually be all the harness sections that are going to need to branch out of our harness down this end of the harness taken care of now.
16:05 There is still an oil metering pump fitted to this engine but we have actually chosen to delete that for our application.
16:10 We're going to be running pre mixed oil in this.
16:12 It's simply because we are going to be running many different ECUs in this vehicle and not all of them have the facility to run the oil metering pump.
16:20 So we are just going to delete it for simplicity.
16:23 Moving back down our harness I'm going to think about our next branch point and the harness sections we're going to want to be coming out of the harness there.
16:32 In particular the next sensor that we're going to need to make a connection to is our intake air temp sensor.
16:37 That lives on the bottom of our upper intake manifold which is currently not fitted to the vehicle.
16:43 What I'm gonna do in this instance is I'm going to attach a section of rope that's a little bit too long and I'll trim it back once I've got that upper intake manifold in place.
16:55 Now other harness sections that are going to come out of that same branch point are going to be the sub harness connectors for our turbo system.
17:04 Now we've mentioned it's the case, quite often you're working in an engine bay and not all the pieces of the puzzle are quite here yet.
17:11 Definitely the case with our turbo system.
17:13 I do know that we are going to be having two exhaust gas thermocouple sensors, one per rotor housing, wideband O2 sensor and dual wastegate position sensors as well for the external wastegates on that system.
17:27 So I am going to have to wire for all of those.
17:29 And we're going to have another sub harness connection for that.
17:32 So I'm going to branch that sub harness connection out from the same branch point for our intake air temp sensor.
17:39 And there's another nice threaded boss on the back of the engine here that I think I'm going to pick up on with another wee mount for that sub harness.
17:48 A very similar story with our gearbox connection as well.
17:52 So there are some OEM electronics that we still want to work in this vehicle.
17:56 In particular the original speedometer and the reverse lights.
17:59 We are gonna have to run that wiring through this wiring harness, so I'm gonna have a sub harness connector for that too.
18:05 Just mounted on the top of the gearbox here so I'll be branching that out at the same point as well.
18:30 Also from our second branch point that we've created here, we're going to be having the harness section for our throttle position sensor sub harness connection as well.
18:40 Now we're using the sub harness there because we know in the future we are going to be wanting to upgrade the vehicle to use an e throttle.
18:48 So initially it'll be going together with the factory cable driven throttle and the OEM throttle position sensor.
18:54 In the future we'll fit an e throttle to it so I'm going to need the wiring there for the H bridge driver to control that e throttle and the dual throttle position sensors that you require for an e throttle application.
19:06 So like I have done with our wiring for our intake air temp sensor, I'm simply going to attach a piece of rope there that's a little bit too long.
19:16 I'm going to get our upper intake manifold in place and then trim that back to the length it needs to be.
19:52 Got our intake manifold dummy fitted into place here as that's gonna let me trim our harness section for our intake air temp sensor which is actually just under here and get that the right length.
20:04 I've got a bit of tape pre prepared for that as I'm going to have to do a little bit of a contortion act to get this bit of harness the right length and then pull it out again and get that tape in the right spot so I can trim it to length.
20:21 Now also with that intake manifold in place, it's letting me see where's gonna be a good spot for the sub harness branch for our throttle that I was talking about before and I think I'm actually just gonna loop this back a little bit, right in behind the motor here and attach it onto this water pipe that's running along the firewall.
20:41 There's not gonna be any amazingly hot water going through that so it's not going to be a heat source I'm going to be worried about damaging our harness.
20:48 It is a nice tidy spot that I'm gonna be able to get a cable tie around and do a good job of mounting that connector.
20:55 It's gonna be a little bit tricky to see in behind the inlet manfold here so I'll whip this off quickly and show you where we're gonna mount that.
21:06 This is the branch here we're talking about and it's simply going to loop back and attach on to this heater pipe here.
21:13 It's gonna give us a couple of options down the line for mounting that.
21:16 We can simply cable tie to it or if we want to get really fancy, we could probably have some sort of clamp mount on here that would hold the flange connector really nicely.
21:26 Right before things get too complicated here, what I'm going to do is get some painter's tape and just mark all the ends of our harness here, a bit of sharpie on there to let me know which connection was which.
21:38 Once you get a few of these branches in place, it can be remarkably easy to lose track, particularly if you've got two branches that are very similar length.
21:46 So it can be a bit tricky to figure out later on which was which.
21:48 I'm also going to add in a couple more harness sections to our branch point down here that are going to head to our engine oil pressure and engine oil temperature sensors that are going to be part of our oil filter block underneath the oil filter here.
22:02 The last part of the process is then going to be trimming back the main harness trunk here to the right length to fit our bulkhead connector.
22:13 Now this is exactly the same procedure that we've shown in the practical wiring course, so I'm gonna go ahead and get that done now.
22:21 With the main harness route in the RX7 established, it's a good example of a common theme in a motorsport spec harness.
22:26 And that is that the sub harnessing often makes the initial routing job much simpler.
22:32 As an example, for our fuel injectors, instead of needing to consider each injector separately, in our main route, we've only considered the injector sub harness connector.
22:42 Now this is absolutely not a shortcut and we still need to consider the placement of the individual injectors, but considering them in isolation certainly makes the job easier.
22:52 Plus we get the benefits of being able to remove and upgrade the fuel system on the vehicle without needing to modify the main harness.
22:59 The draw back to our sub harnessing is obviously going to be cost as we are adding another connector and associated materials into the harness.
23:07 But I find most often the benefits do outweigh the cost.