Chris Lockhart

Been doing plenty of searching, and haven't found anything. Anyone have one or know of a good write-up somewhere? I know plenty of you have done this, but haven't documented the fun. I would really prefer to build my own, so any/all help is appreciated.

Mrmerlin

I did read that you thought it would be fun to build your own....BUT WHY experiment?

Pick up the Phone,
Call Roger 928sRus,
Order a S4 wiring harness,
Write a check,
Put into post,
Wait 8 days,
Open shipping box,
Remove new harness made by Sean,
Install said harness,
Drive the car.

Chris Lockhart

Would you take your car to the dealer for a timing belt/water pump job Stan? Nope. Same here. I have the basic knowledge and tooling to do the job, it would just be a little easier if someone who had BTDT had a nice tutorial. (Just like so many have used John Pirtle's timing belt tutorial for that task.) I'd rather do it myself, but a little bit of guidance is always helpful. If not, so be it. I'll just buy the parts from Roger and muddle through. :-)

hacker-pschorr

Building a harness is a lot different than doing a timing belt job. It's a "part" not a job.....well a bit of both I guess. Equating the two would involve rebuilding your own water pump......

Years ago I invested heavily in the proper crimp tools, loom, wire, connectors etc.. to build my own harnesses. This was before Roger sold them and I also had two stand alone projects in the works. I never solder crimp ends and I use the most modern weatherpac style connectors. This doesn't look remotely stock which turns some off.

Honestly it's one of those jobs that if you need a "how-to" you probably shouldn't do it. You lay out the old harness and copy it, that's pretty much it. Very fiddly work making sure all the looms come together correctly, a lot of personal preference on what kind of loom you want to use (what I have on hand is nowhere near stock, but I like it better). Some trial / error etc....
I ordered a lot of product to "test" how it feels, cutting it etc.. some require a hot knife, some fray worse than others etc....
I use a lot of tiny zip ties to keep things in the proper location as I go along.

Also buying the quality wire in different colors etc... Quality German or US wire is not cheap, and gets very tedious if you want to keep similar or same color combos as the factory wire. Just imagine ordering a spool of 50' in every color. I tend to use Wurth wire, which you can get from Roger.

I enjoy doing wiring jobs and I'm about to start another to convert my 79 to something other than CIS. Probably going with AEM Infinity. Attach the box, lay out all the wire and work backwards......

It's a fun learning experience, but to do it right is a huge investment.

dr bob

Chris--

As H-P shares, the fun starts when you go shopping for the conductors. Economically, it would be so much easier to do as the CE panel is done, all in one color. But none of us, to my knowledge, are ready to do that. So you'll be shopping for a dozen different 10' spools of wire. The connectors are all available, except for the later oil pressure sender connection. Then you may want to try and match the original plastic sleeve for the forward part that shows when you open the hood. Sections closer to the exhaust can use some of the more modern protection, like Firesleeve, as the GB, Carl, 928 International, and Roger/Sean harnesses can do. Upgrading the primary conductor sizes supports the additional electrical loads many add when they put electric fans in early cars, do high-wattage headlight and other lighting projects, etc. Then... you get to assemble it all, with properly crimped and sealed connectors. And test/verify it all before installing it in the car. Or risk damaging some component.

I admit that I'm the biggest fan of DIY stuff, and wouldn't hesitate to source all the pieces needed to build a harness. I have most of the the tools already, and know where to buy stuff. The pragmatic side tells me to just buy a known-good piece; even reducing my dollars-per-minute billing rate to dollars-per-hour minimum wage rates, a GB or SeanR harness is still a bargain IMHO. It turns out that time is a non-renewable resource. There's an infinite supply, but only a tiny slice is available to me. I could spend it enjoying other things.

Mrmerlin

Chris I am a mechanic and my time is worth a lot ,
you asked for a tutorial,
this is how I would proceed.

Its a lot less time consuming to not have to reinvent the wheel when its already been done .

So in the end how much is your time worth?
How much money do you want to spend buying the necessary parts?
how many times do you want to rework your efforts?
How soon do you want to be driving your car?
Its a whole lot easier to open a box and layout the new harness,
hook it up,
clamp it into place,
connect the battery,
and start the car.

Building a good wire harness is not equal to replacing a timing belt IMHO,
and building your first harness will cost YOU a whole lot more of YOUR time and effort than buying a good harness thats already been proof tested

M. Requin

I have done three vehicle wiring harnesses: an MG-TC (I think that took 6 wires, no, maybe eight...), a 60's Detroit V8, and a 37 foot yawl with full electronics and accessories, from radar to desalinator (not really a harness, more point-to-point wiring, but same principles). To me the above quotes say it all. And for me the biggest problem I found when looking at replacing sections of my 928 harnesses, which need it, is sourcing the proper wire. I'm **** enough about this stuff to use only tinned multi-strand with the right insulation colors (and like H-P I only crimp, per ABYC standards, although I just recently saw some "hybrid" crimp/solder/heatshrink stuff that looked pretty cool), and so far that has been a show stopper. I know I can document the changes in colors, but far I don't want to go down that road. But when and if I pull the engine I probably will. It's a WYAITWN. (I added the Why Not...)

dr bob

I've done the same projects as Martin, plus some early F cars and more British stuff than I care to admit. It's tedious at best. The marine projects take at least as much planning as fabrication, FWIW.

Maybe at some point one of our vendors will build a "kit" of conductors and connectors and sleeve pieces, so those of us who feel we can do a better job can give it a try. I can buy 1000' spools for a lot less per foot than the ~~10' lengths in the harnesses. But I won't ever have 100 928 harnesses to build either.

Parents, teach your school-age kids a valuable lesson! Sponsor them in a little cottage industry making 928 wiring harnesses. They'll learn valuable workmanship skills, time management skills, and earn the next few dollars needed for their college funds. Plus, after doing this for a while, they'll have a better appreciation for the value and benefits that come from that college education.

Or just buy one already tested and proven.

BauerR

What are new wiring harnesses going for? Totally interested.

Speedtoys

Im sure GB or SeanR could, and lower their bulk costs for the harnesses that they build and sell..but..

I dunno, this is way way too leaning towards the EZ-Button of ordering a prepared harness and installing it, and the whole click to start processes being about 4 days long, including shipping.

M. Requin

Love it!

dr bob

Here's the result of a bit of time in the WSM Wiring Diagrams for my 1989 car. KS2 is the Front of Engine Harness that connects at the 14-pin T18 connector on the right fenderwall, and to the jump post. At the other end, it includes primary power connections between the battery terminal on the starter, the alternator, the ABS unit, and the jump post.

The MM^2 wire sizes are from the WSM drawings. The equivalent AWG wire size is shown, rounded up to the most common conductor sizes available. Some of the sensor wires shown as 1.0 MM^2 could probably be 18ga instead of 16ga as shown. There are physical durability considerations that suggest that 16ga is a better choice though.

I don't have the conductor lengths, as my only good harness is still in the car.

Chris Lockhart

I appreciate all of the input, both positive and negative. It's not an issue of being able to swap the harness and fire up the car in a week. In general I'd prefer to do as much myself as is possible (and yes sometimes practical does enter the equation.) Currently being that the engine is still out of the car, and the harness is available to use as a template to make a loom/peg board, and I'll be on hold for other issues/components, I felt that doing my own harness was a realistic project. Although I'm no electrician nor Avionics tech, I am a licensed aircraft mechanic with 30+ years experience, and have done my fair share of pinning/de-pinning cannon plugs, crimping various connectors up to 1/0 AWG, routing wires, and helping to create new harnesses on a loom/peg board. The basic principles are not an issue, and neither is access to the proper crimping equipment. I just felt that out of the folks who had built their own harnesses maybe there were some "gotchas" or "be careful of" or "this new style connector is much better if you're not worried about being totally stock", etc, type bits of info. Maybe "tutorial" was too strong a description of what I was asking. Thank you all. The input is appreciated.

Mark R.

So roughly how much does the readymade harness cost from our usual suppliers?

That seems to me like an entire critical half of this discussion that is missing.

One always needs to know what you're trading your time and effort against...

.

FLYVMO

Hi Chris,

It is all well within the capability of most DYIs, and pretty fun actually (call me weird). In my project I replaced EVERY harness (ABS harness soon but not yet) in the car with fresh wiring, including upgraded wire gauge for certain marginal cable runs. There is a fairly decent selection of great connectors available, Deutsche Motorsports or aero style connectors that are weather sealed. It all comes down to how much you want to spend on them. It takes time to reference the amperage limits of each connector, and based on how many wires and current it needs to hold, then pick the connector of choice. Most connectors on later 928s are pretty sturdy, and should have a fairly negligible loss. They are however pretty big and clumsy and the slim Deutsche Motorsports connectors are a great option. Same with aero-style connectors. If you are not worried about retaining the "factory" setup for originality, then go for it. If you intend to keep your car indefinitely, then at some point your +25 year old wiring WILL need attending to anyway.

It's great therapy!
Carl