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Practical Wiring - Professional Motorsport: Step 4 - Generating Your Construction Plan

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Step 4 - Generating Your Construction Plan


00:00 - The fourth step of the HPA 10 step motorsport harness construction process is generating our construction plan.
00:07 At this point in the process we have all of our design done.
00:11 We know where every pin is crimped, every wire is spliced and how everything is layered and branched out.
00:16 The temptation at this stage is to dive right in and start cutting wires.
00:20 But it's imperative before we begin the physical build process that we have a complete plan for how the build will progress from start to finish.
00:28 When compared to building a club level harness where we were able to lay out all of our wires onto our build board, bundle, sheath and then terminate them in that order.
00:38 The concentric twist construction we use on a motorsport harness and the general tighter tolerances overall make this method hard to use and get a good result from.
00:47 In particular the small circular cross section of our motorsport harness sections means we're often able to use a smaller size of heat shrink sheathing, which may not be able to fit over complicated branch points to reach all the harness sections.
01:03 This means that these harness sections will need to be sheathed before those branch points are finalised.
01:09 The flipside of this is that if we're using large circular motorsport connectors for interface connections, these can be much more difficult to tidily terminate a completely sheathed harness section to.
01:20 By thinking through the build process before we begin, we can avoid as many of these issues as possible and minimise any issues that reman.
01:29 Like every stage of the harness design process, compromises will need to be made and experience will play a role in determining the best compromise.
01:38 But most construction plans will end up following a similar path.
01:42 We start at the end of the harness that contains the most complicated connectors to deal with.
01:47 Usually this will be the bulkhead interface or ECU connectors.
01:51 The harness sections heading away from these connectors are built up, bundled, sheathed, and labelling materials slid into place.
01:59 These sections are then combined at the first branch point along the harness.
02:04 And the harness sections heading away from this branch point are then built up and sheathed.
02:09 The construction process follows along in this way from one end of the harness to the other.
02:16 Building the harness in this way makes it much easier to pin the large interface or ECU connectors and ensure those large harness sections have an excellent fit.
02:25 A few millimetres of extra length on a harness section that ends in a sensor connector for example is not likely to be a big deal.
02:33 But it will be very noticeable in an area that has many large connectors, the spacing of which is determined by the device or the mount that they connect to.
02:42 We'll have a look at the construction plan for the harness to fit our FD3S in detail now.
02:47 We'll have a look at how we've constructed that plan and the decisions that have been made.
02:53 You can see we've got a simple document here that is separated into individual build stages.
02:59 So these are the very distinct build stages that we're going to follow through in order that will result in us building our complete harness.
03:08 Each individual build stage is then broken down further into more granular steps.
03:14 This is a really good idea as it's going to help you ensure that you're not going to miss any important details and you'll be able to keep track of where you're up to far more easily if you get interrupted during a particular build stage.
03:27 Having a look at our first build stage here, we're going to construct the harness section that is going to head from our sensor interface bulkhead connector to branch point A.
03:38 Now the first part of this build stage is going to be prepping the core wiring from our sensor interface connector.
03:45 Remembering that the core wiring has been designed to match up with the pin out of that sensor interface connector so it is going to be in the centre of that connector and we do want to pin that in first as it's much harder to pin that later once we've got wires on the outside of that connector pin out.
04:02 Now the core wiring in this instance is simply our CAN bus wiring, so that's going to be a simple twisted pair, there's going to be no splices or solder shields to deal with so that's going to be very simple.
04:12 Once we have that wiring terminated and pinned into place, we're going to start on the first layer of our concentric twist plan for this harness section.
04:22 And remembering back to our design, that's going to include five twisted shielded pair cables.
04:27 Our two thermocouple wires and our three twisted shielded pairs there.
04:31 So we are going to need some solder shields to be installed here to make a connection between our shield braid out to an individual pin, which will make the pass through from that interface connector to the interior of the harness.
04:44 Important to put a note about that in here as it may alter the way you actually build that harness section.
04:49 Once we have that wiring pinned into place, we're going to twist that layer one wiring around our core, making a note there that it is going to be a left hand lay.
04:59 Now an interesting point about the harness design for our FD3S here is that once the exhaust gas thermocouple wire has actually split off from our main harness section at branch point A there, our three other twisted shielded pair wires, being our engine sync, ref and our knock sensor signal are actually going to form the core of the harness for the rest of its run.
05:23 So that means we can go ahead at this stage and actually twist our core wiring from branch point A to B and actually from branch point B to C.
05:33 This is really good to do at this stage as it's going to keep those three individual wires nice and tidily bundled together, it's going to make them much easier to organise while we're working on the rest of the wiring in the harness.
05:45 The next part of the process is going to be prepping our layer two wiring from that sensor interface connector outwards and this does include some splices, particularly our sensor supply and our sensor ground splices.
05:58 So this is the point where we're actually going to undertake those splices as we're going to be pinning a single wire into that interface connector, which is then splicing out to the multiple wires which are twisted into our harness.
06:10 So that splice is going to be located right behind the interface connector there beneath the boot, so we are going to undertake that at this stage.
06:19 Once we've got that splice done and that individual wire pinned into place, we can twist all the wires from that splice point into the harness there.
06:27 A good note here, it is going to be a right hand lay at that stage.
06:32 Following on from that, we're going to be prepping our layer three wiring, that's going to be a nice simple prep, but there is a note here that we are going to have to include some filler wire to round out that layer and make it complete.
06:45 At this point, what we're going to have is all the wiring from our sensor interface connector tidily concentrically twisted and bundled together in that harness section heading to branch point A.
06:57 It's not yet going to be sheathed, we're going to put that to one side and we're actually going to start work on our actuator interface connector.
07:04 Now this is going to be a very similar process to what we've just done, we're going to prep our core wiring and get our core constructed.
07:11 Then working through our layers, making sure that we've got our lay lengths and our lay directions correct, and we are including that filler wire.
07:21 Once we've got those two harness sections all twisted together and bundled, and they are terminated to their connectors now as well, we're going to have to test fit them to the mounting plate that's going to be in the vehicle.
07:35 And by doing this it's going to allow us to very tidily line everything up and ensure that all our lengths are completely correct.
07:43 Once we've got those lengths correct, we can cut our sheathing to the required length and actually get that installed on those twisted harness sections, and we're going to recover that in place now.
07:55 Once we've got that recovered into place, we can install our labelling material up to those connector locations.
08:03 And that's really important to do at this stage as once that branch point is finalised and those two harness sections are actually merged together, there's not going to be another opportunity to get that labelling material in place.
08:16 Now it might seem like it would be a similar story for the actual boot that is going to connect the connector to the harness section but that's not the case because we're using large shrinkable moulded shape boots and they are large enough to actually fit over the connectors.
08:33 So we can get those installed as almost the last step of our harness construction process.
08:38 With those two harness sections, the correct length now and fully sheathed, we can install the branch point A boot and we can actually begin the construction process of merging those two harness sections together at branch point A.
08:51 Now we've just talked about build stage three there which was sheathing the harness sections from our sensor interface and our actuator interface connections to branch point A.
08:59 We're now going to move into build stage four and that's going to be building our harness sections from A outwards down the rest of the harness.
09:08 So the first thing we're going to have to do is group all our wiring at branch point A into the harness sections with the correct orientations.
09:16 Now this is the point where we're going to take our sensor interface branch and our actuator interface branch and actually merge them together at that branch point A, following the rules that we've talked about in the brancing lesson section of the course.
09:30 We're going to try and keep that branch section as tidy as possible, but we are going to be completely strain relieving it with some kapton tape.
09:37 The key here is that we get all of the other branch sections that are going to be exiting that branch point in the correct orientations.
09:46 Once we've made sure that we've got all of those in the correct orientations, we can continue on with that build stage four, that's going to be twisting the wiring that is in layer one from A to B with a right hand lay, and then twisting the wiring which forms layer two from A to B in a left hand lay.
10:06 Now we're doing this before we deal with any of the other harness branch sections as there's going to be quite a lot of wires in that section and getting them all out of the way now is actually going to make dealing with those smaller harness sections heading away from branch point A quite a lot easier.
10:22 Once we've got all those wires into place, we can form the core from A to our exhaust interface and layer one of that branch section as well, following through in the same way for the rest of the harness sections that are going to be exiting branch point A there.
10:40 The next part of the process, build stage five is going to be sheathing the harness sections from A outwards.
10:46 So this is going to be putting the sheathing on all the harness sections that we have just constructed.
10:51 What we're going to do at this stage though is actually undertake a test fit on the vehicle.
10:57 Now if you're building the harness and you have access to the vehicle, this is a really really good thing to do.
11:03 It's going to really help you get the best fit for that particular application.
11:08 However it's not always going to be the case.
11:11 If you are building motorsport wiring harnesses as a profession, chances are you are going to have designs sent to you.
11:19 At this point, instead of doing a test fit on the vehicle, you would definitely do a review of the design that you've been sent and ensure that the harness lengths that you've finalised at this point are actually meeting that customer design.
11:33 To continue build stage five, after we've test fit and ensure that we've got the correct length of all our harness sections, we're going to sheath all of those harness sections the correct length and then we're going to install the unrecovered branch point B boot.
11:49 Now both of the branch point boots that we've installed at this point are still going to be unrecovered even though we have recovered all of our actual sheathing.
11:58 Recovering those branch point boots is going to be one of the last steps that we're going to undertake as at this point it is still possible to make a change to the harness if need be.
12:09 But once those branch points are completely sealed and potted, things do get much harder.
12:14 The build now progresses through to build stage six which is the harness sections from branch point B outward in exactly the same way as we've previously done and build stage seven which is sheathing our harness sections from B and C outwards does have a slight difference here because we're actually going to be sheathing the sections from two branch points outwards.
12:36 And that's just because our last branch point is very very simple.
12:40 It's our three twisted shielded pair wires so there's not actually going to be any concentric twisting once that branch point is finalised required as it is just an individual twisted shielded pair cable heading out from that point.
12:55 You can see from this construction plan, we are starting with the most complicated connectors on the harness, the bulkhead interfaces.
13:04 Installing and twisting all their wiring before we lock in their reletive lengths by building our first branch point.
13:11 This way we can guarantee a tidy fit of these two harness sections.
13:15 You will often find yourself in the situation like this where you have multiple large harness sections that terminate to a single device.
13:23 The bulkhead mounting plate in our FD3S RX7 example here.
13:28 Now that defines the connector spacing.
13:31 While it's not impossible to terminate the wires tidily to the connectors after the rest of the harness is built and sheathed, it's much easier to get a tidy result by approaching the build like we've outlined here.
13:44 The rest of the harness build extends out from this point following a branch twist sheath and boot process.
13:51 By formalising a plan before we begin, we can ensure that none of these steps are missed.
13:57 Once you have a few harness builds under your belt you may very well be able to look at a harness design and know how it should be built almost immediately, but we would strongly recommend generating a formal constrution plan like this for at least your first couple of harness builds.

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