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Practical Wiring - Club Level: Step 2: Layout and Routing Design

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Step 2: Layout and Routing Design


00:00 - So this is the second step of our HPA eight step process, which is the physical layout and routing design.
00:06 This is designing how the wiring harness is going to run throughout the engine bay and the interior of the vehicle.
00:12 We undertake this process out here physically in the vehicle using that rope, laying it onto the engine and determining how long each branch is going to have to be to reach our actuators and sensors and where each branch point needs to be also.
00:26 So we're gonna go ahead now and look at this in detail in the engine bay of our FD3S RX-7 here and show you how to go through the process of determining where the wiring harness is going to have to run and where those branch points need to be.
00:38 So with our nylon rope here I'm going to start laying this on top of the engine, figuring out where we're gonna want our main harness trunk sections to run.
00:46 So in this instances we are going to replicate a lot of what the OEM did, and we're going to run this along the top of the engine here.
00:54 Which is going to use the intake manifold as a barrier from the heat of the exhaust.
01:02 And once we've got this lined up in place we can determine where we're gonna want our main branch points to be, to then head out to all the sensors.
01:11 So I'm just gonna figure out where, on which side of these fuel lines I'd like this to be.
01:17 I think I am gonna want it to be on this side as it's gonna let us branch out nice and tidily and get to our fuel injectors here in a reasonably straight fashion without needing to have severe right angles or any loss of strain on this connections there.
01:33 So other sensors we're gonna have to interface with are going to be the eccentric shaft position sensors, which on these 13B-REW engines are down in the front here.
01:43 So to interface with those I'm actually going to bring my rope a little bit further through to give me a wee bit of extra length and we're going to end up tucking it down the front of the engine here and this is actually once again the same way they routed them from the factory as it does keep it away from any of those spinning components on the front of the engine.
02:03 All our wiring harness connection's gonna be in behind that which is gonna be really important.
02:08 So with the main trunk of our harness laid on top of the engine as we're going to want it to be routed, I'm going to put a couple of cable ties to various components just to keep that section of rope securely in place so we don't lose its position and then we're going to look at determining where we're going to branch the harness out to reach all of the individual sensors and actuators that it is going to need to interface with.
02:32 So I'm just going to make a quick cable tie connection up the front here to one of the oil metering pump feed lines.
02:37 These can actually be slightly fragile so we're only gonna make this a lose connections.
02:42 Let's just keep our reference point on that rope.
02:45 Once again always flush cut your cable ties so you're not going to cut yourself open when reaching down next to them.
02:52 And we'll just find a point to cable tie this at the back here as well.
02:56 One of those fuel lines is gonna work well for that.
03:04 There we go.
03:05 So you'll notice I've got the rope heading out of the engine bay over the fender here, that's gonna be OK for the moment because we know in this situation that the sealing grommet where the wiring harness is gonna pass through the firewall is down in this corner of the engine bay.
03:18 So I'm going to do this procedure essentially in two steps.
03:22 I'm gonna work out all the routing in the engine bay, we're then going to pass this section of rope here back through into the interior and work out the routing in there in a separate step.
03:32 Often when you're designing this routing harness plan in the engine bay, you are gonna have to do a little bit of mechanical disassembly or reassembly.
03:42 In this instance because we're running the wiring harness on top of the engine here, I haven't actually got the upper intake manifold removed.
03:48 There are some sensors that we're going to have to interface with on that upper intake manifold and it is going to, having it in place is going to help us determine where our branch points are going to be to keep everything nice and tidy.
04:01 So I'm just gonna get that up our intake manifold now and temporarily install it and we're going to get a couple of reference points to determine where those sensor locations are and that will help us figure out where our branch point needs to be.
04:13 So as you can see with our upper intake manifold there it would actually be quite tricky to work underneath that which is why I had it removed but on the back of the upper intake manifold here we do have the throttle position sensor and also the idle control valve.
04:25 Now these sensors are essentially in line with the side, the edge of our engine here so I'm gonna use that as a reference point for determining where my branches are going to be.
04:37 Also keeping in mind that the connectors on these sensors, we're actually going to interface with from this direction, which means we're probably going to have our main harness branch out and then the connectors that come up to these sensors and actuator are going to loop back and interface from this direction.
04:52 So with the location of those determined and our upper intake manifold removed once again, the obvious location for our branch point is actually going to be on top of the gearbox here.
05:02 And I'm going to locate it in line with the edge of the motor as that is going to let us branch everything out to get to our injectors and our sensors up this end of the engine.
05:13 But it's also going to let us loop those back around to interface with the sensors on the back of the upper intake manifold there.
05:21 That being said, I'm not actually going to branch out every sensor and actuator connector here, we're still going to have a combined trunk heading along to the front of the motor here where I am going to have a second branch point.
05:32 The reason for this is it's going to look a lot tidier and we've got quite a lot of space up the front of the engine here for a branch point and it's going to be a nice logical spot for the harness to branch out to get to those engine position and speed sensors and also our knock sensor.
05:48 So what I'm going to do now is I'm gonna get a wee bit of insulation tape and I'm just going to use it to mark those points on the harness.
05:56 So we can use them as a reference and then we're going to cut some more sections of rope and begin building up our mock up.
06:11 Right I've got those harness branch points marked with a little piece of electrical tape now.
06:16 It's always a really good idea when you're undertaking this process to actually take photos on your cellphone while you're progressing through it as they can be a really good visual reference to refer back to later on if you've gotten a little bit hazy about how the wiring harness was actually going to lay on the engine and be routed through the engine bay.
06:32 So our next step is to take another section of rope and determine how long it's going to have to be to reach from that branch point to the actuator in question.
06:41 In this case we're going to look at the rear primary injector.
06:47 So I'm now going to take that section and tape it to our main harness trunk here at our branch point and that's going to give us the section of harness from that branch point that's going to head off to this injector.
06:59 The process continues on like that with us adding more sections of rope required to interface with all of the sensors and actuators in the engine bay, it is very much a rinse and repeat process so we're gonna go ahead and undertake that now.
07:41 Now that we've got our harness mockup built, we've removed it from the engine bay and we've got it laid out here on our studio bench.
07:47 A couple of things I've done to keep it a little bit more robust and easier for us to get the information out of is I've gone ahead and taped up these branch points with some extra insulation tape to make sure they're nice and robust and they're not gonna fall apart while we're dealing with it here out on the bench.
08:03 I've also gone and put some painter's tape on the end of each of these branches and then just written in sharpie what that particular branch is interfacing with.
08:10 What I'm going to do now is take a white paint pen or a twink pen like we have here and make a mark on our branch points that becomes a reference location that we will take all of our measurements from.
08:22 We want the measurements of all of our harness sections here to be from the same point to make sure we get the right length.
08:29 So I'm gonna go ahead and just mark on these branch points, that reference location.
08:38 With the reference points marked on our branch locations here we can go ahead and begin the process of measuring all of our harness sections and using that to generate our documentation.
08:48 Now the first harness section I'm actually going to measure here is this central trunk.
08:52 This is a fairly typical harness build in that it has a central trunk through which most of the wires pass.
08:58 There's a branch point on either end, one side's in the interior and the other side is in the engine bay.
09:03 So we're going to line up that reference point here with our 600 millimetre mark on our roller and I can see the other side here is lining up 950 millimetres, so that means the length of our trunk section here is 350 millimetres.
09:18 Gonna go ahead and draw that on my documentation.
09:23 350 and we will use that as the starting point for generating the rest of our documentation as it branches out from that central trunk.
09:33 I'm gonna go ahead and do that now.
10:01 So with that process undertaken we've now got our physical harness layout document prepared.
10:05 A couple of important points to note here is that this document is not to scale.
10:09 However we have clearly denoted on each of these harness sections, the length of that section and the part of the harness or EFI system, that it is terminating to.
10:19 Another important point we've noted here is that the main trunk of the harness passes through the bulkhead sealing grommet 90 millimetres from our interior branch point.
10:29 And that's going to let us know where to locate that bulkhead sealing grommet.