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Practical Wiring - Club Level: Step 5: Sheathing

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Step 5: Sheathing


00:00 - The fifth step of our HPA eight step harness construction process is the one of sheathing our bundled and branched bare wire harness.
00:09 We do this to add protection to the wires and in this instance we're going to use raychem DR25 for the job.
00:15 Now this step has three distinct processes, the first is determining the length of the section of DR25 you're going to have to cut, and you have to remember to account for the raychem SCL boot that is going to be at either end of that section of DR25.
00:31 The second is then determining the diameter size of DR25 that you're going to need, and we do this by measuring the diameter of the harness section that we're working with.
00:40 The third is then installing those sections of DR25 onto our harness and recovering them in place with our heat gun.
00:47 Now we do this working form the centre of our harness outwards.
00:50 A typical harness construction is going to have a main central trunk, which is where the harness is going to pass through the firewall, and this is going to be the largest section of the harness.
00:59 For that reason we want to get that part of the harness sheathed first, as if we sheath the rest of the harness, it is going to increase the diameters of those sections and it's going to make getting this piece of central heat shrink into place, quite tricky.
01:12 So you can see we've got our central trunk section sheathed here and that is recovered down.
01:17 From here we're going to work outwards, we're going to look at the interior section of the harness here.
01:21 We can actually work with any of these branches at this point, the order in which we do these is not going to be important.
01:27 So I'm going to select our power supply branch here and we're gonna get a diameter measurement there which is gonna let us know the size of DR25 we're going to need, and then we'll go through the process of working out the length that we're going to need to cut.
01:40 So we'll go ahead and measure that diameter now.
01:47 We've got approximately 10 millimetres there.
01:49 So that's gonna let us know the size of DR25 we're going to have to use to recover onto this harness section.
01:57 DR25 having a shrink ratio of 2:1 means we're going to take that 10 millimetre measurement and we're going to double it, giving us 20 millimetres, and then choose the closest size of DR25 to that, that is still smaller than that 20 millimetre measurement.
02:11 In this instance, that's going to be 3/4 of an inch DR25 which is almost exactly 19 millimetres.
02:17 So that's gonna give us a really good fit when it's recovered onto this harness section.
02:21 Next step of the process is going to be to determine the length of DR25 that we're going to need to cut, making sure that we account for the SCL boot that's actually going to form our branch point here.
02:32 Now there's two ways to go about this, we can either refer to our documentation and go from there.
02:38 But when we're building the harness out on the bench here, it's usually easier to just measure the harness section with our sewing tape measure.
02:44 Because it's flexible we can get a good accurate measurement of the length of DR25 that we're going to need to cut.
02:50 So I'm gonna make this measurement in a moment.
02:52 I just want to talk about one key factor that we need to take into consideration and that is the length of bare wire that we're going to have on the end of this section.
03:01 Now because this harness section is our power supply, it's got some larger gauge wires in it.
03:07 And for that reason, I'm going to leave a larger than normal section of exposed wires as these are a wee bit stiffer, often they can be slightly trickier to strip and crimp the terminals onto and then manipulate into the correct pins in that connector.
03:21 So I'm going to leave around about 80 millimetres of exposed wire there, take my measurement from that point, back up to our main trunk section of DR25, accounting for the SCL boot that's going to be 50 millimetres long here.
03:35 So I'll get my tape measure and we'll take that measurement now.
03:42 So I've got a measurement of 330 millimetres there, I'm gonna go ahead and get my roll of 3/4 inch DR25, cut off a section 330 millimetres long, we'll get that installed onto our power supply branch and recover it down, it's gonna give us that really nice, tidy, protective covering on the outside of our bare wires here.
04:00 I'll go ahead and do that now.
04:18 So we've got our 3/4 DR25 recovered onto our power supply branch here.
04:23 The wall has thickened up nicely, it's gonna be giving it really good protection to those wires underneath.
04:28 The rest of the process is simply a rinse and repeat.
04:31 I'm gonna continue to work on the interior section of the harness here, recovering DR25 onto all these branch points.
04:38 We're then going to start on the engine bay part of the harness, working in that centre out fashion.
04:44 So I'm going to recover DR25 onto all these branch sections, one of which is actually another trunk that has branches coming off it, so we're gonna make sure we recover DR25 onto that trunk section and then onto the following branch sections that come off that.
05:02 So I'm gonna go ahead and get that process done now.
05:39 So now we've got all our DR25 recovered into place on our harness.
05:43 Couple of details definitely worth noting, when I was undertaking that recovery process, it was pretty apparent that it was going to increase the size of the branch points as they exit out to all the smaller harness sections, and that was going to limit our ability to get our SCL boots into place.
06:00 So after I'd recovered this centre branch section, I actually went ahead and installed the SCL boots while I still had the bare wiring out either end of the harness and then that was actually the same story for the other two branch points as well.
06:14 Just really good to always think through that entire build process as you're working and make sure you're always gonna have access to get a piece of heat shrink onto the part of the harness that you need to.
06:25 Anther thing we've done as we've finished off that DR25 sheathing process, is just use some of our kapton tape to tightly wrap the branch points, that's just gonna give them a little bit more support and it's going to make installing our sheathing boots much easier.
06:40 Also when we recover these sheathing boots, they are going to grip the harness quite tightly.
06:46 So having that kapton tape underneath is gonna avoid any sharp edges showing through and give us nice fillets in there.
06:52 So the last part of the process now is indeed recovering our SCL boots into place.
06:56 First thing we need to do here is go ahead and abrade the DR25 at either end of this branch point here.
07:04 So I've got some 120 grit sandpaper, I'm gonna go ahead and scuff this up, give it a clean with isopropyl alcohol, and then we'll talk about the positioning of the boot.
07:32 With our DR25 sheathing nicely abraded, all cleaned off with that isopropyl alcohol, we're gonna slide our boot into place, and we're looking to line up the centre of the boot here with the centre of our branch section.
07:44 So we'll get that into place.
07:47 Now I'm gonna head over to our heat gun and I'm gonna recover that down.
07:56 So with our SCL recovered into place there, we can just have a look for those last critical details, got our sealing bead at either end here.
08:04 So we know that has recovered properly and that potting compound has flowed.
08:08 And we've got our last line of defence as far as strain relief goes, and that's our cable tie on the branch transition point exit.
08:17 Now the rest of the process is exactly the same as what we've pictured here.
08:21 I've got my sealing boots in place, I've got to go ahead and abrade those DR25 sections, give them a clean with the isopropyl alcohol, and I'm gonna get those boots recovered into place.
08:31 Gonna go ahead and do that now.
08:49 So with our SCL boots recovered into place, that concludes the fifth step of the HPA eight step harness construction process.
08:56 We've now got our protective covering over all the wires of our EFI harness, which are going to allow it to withstand the harsh engine bay environment, and just the automotive environment in general.
09:07 The next step of the process is going to be creating and installing the labels that will be on the ends of all our harness sections and also preparing the boots we will recover onto the ends of those harness sections.