Harness Makin'

[Zirconocene]

This is from an '87, to be used as a template for my 2 '90s (S4 and GT).

Hopefully this will make layout much easier in the future.

20240219_144816.jpg (4.45 MiB) Viewed 4538 times

20240219_174701.jpg (5.05 MiB) Viewed 4538 times

Cheers

[blueline]

This is from an '87, to be used as a template for my 2 '90s (S4 and GT).

Hopefully this will make layout much easier in the future.

20240219_144816.jpg

20240219_174701.jpg

Cheers

Impressive organization. Nicely done - I love it!

[Tom]

Looking good!

[dr bob]

Wow!

Do the 928 world (actually me...) a huge favor and build the wire table list (by gauge/colors) for this harness. Beyond a nail-board, some wire lengths and a real diagram would be awesome! I can help with stuff from the wire diagrams like colors, connectors, pin numbers. Wire lengths and the section length would be awesome.

For those playing along at home, this is the top-of-engine harness for S4+ cars. Harness is pretty consistent from '87 thru end of production in 1995. This includes sensors (Crank position, knock sensors, airflow, some temps) plus the injectors and vacuum actuators, idle switch, idle air control valve, more. It's the most fun harness to build and install.

It's on my list of casual things to build/replace on my car. I have the schedule/plan for the front harness (KS-2) but not this one. Yet.

LMK if I can help or participate in your build exercise.

[Drscottsmith]

Here is a diagram I put together from some other folks when I built mine....

The first page is 87+
Second page is 83-84 L-jet
Third page was a start at 85-86 LH cars

The second page is the most complete as that is what I actually built for my car (+ a few extras for friends). We went in and bought the wire in bulk to save some $

[Zirconocene]

@Drscottsmith : That's great, thank you for sharing.

@dr bob : I have a Google Sheets document started that I'll share with folks once I get things closer to finalized. Right now it's a bit of a mess as my notes evolve and I get closer to actually building a new harness.

I went through the same exercise for my 944 S2, but took a bit of a short cut on that car to anticipate future upgrades. While I'll be able to make a brand new harness to swap out for an old one on my 928s, my actual plan is to make the new harness ready to work with an aftermarket ECU, so that I can go to things like sequential injection, coil on plug, and MAP. This should help to clean up the engine bay (no more distributors) and, hopefully, make the car a bit more reliable than the now-long-in-the-tooth components can reasonably handle. For that, I plan to introduce some sealed plugs just after the harness exits the firewall into the engine bay, where all the sensors and electronic components can meet. As the interior electronics get upgraded (LH and EZK, central electrical panel) I'll be able to just reconnect at those plugs, instead of making a whole new harness for the engine.

Cheers

[Drscottsmith]

One note I should have mentioned...

Since doing the 928 harnesses I have also built one for my 951 that is using Microsquirt control. I used 16 gauge wire for most of the 928 harness and that was (in my opinion) WAY overkill. It makes the harness much larger than necessary and even required me to have a new 3D-printed male plug for the 14 pin connector fabbed up to handle the girth of all those fat wires.

On the 951 project, I used the 8 foot MS harness as the base, but had to run home run wires for all of the gauge sensors, etc. I used 20 gauge wire and it seems to be plenty for carrying the low voltage required for these signals. Also, this is marine wire so I think its longevity will be fine.

If I ever did another 928 harness, I would use 20 ga. and not look back.

[Zirconocene]

From what I can tell, the OEM wiring is about 17 AWG (I forget the metric, cross-sectional area). I agree with @Drscottsmith and have used 18g marine wire in my harnesses and repairs, and given the voltages involved, most of the wires can easily go to 20g. However! Certain wires end up carrying the signal or current from multiple points, and those should likely be sized a little more generously (like the injector splice, or the ground wires from the LH/EZK).

That said, I have NOT used TXL sheathed wires and, indeed, it makes for some fat bundles.

Cheers

[dr bob]

Car came off storage stands today. So more fun is in store...

wiretable.jpg (592.37 KiB) Viewed 4365 times

This table and the current requirements for sensors (minimal) suggests that the smaller sizes in the original harness are used for their mechanical rather than electrical needs. I'm more than happy using 18ga in the top of engine harness especially where the connectors and immediate sections are well supported mechanically. The batch-fired injector loops are high enough current that I'd use the full spec size at least to the junctions for the injector pigtails.

Have you found a good shielded-pair cable for knock and crank-position sensors?

[Zirconocene]

Sorry for the late reply; I was travelling on biz and totally missed this.

Indeed, I have found some sources of shielded cable, but not in OEM green. Kroon sells some of that wire, but at significantly higher price than what I've found. I have some extra, if you need some, and am happy to share my sources (provided I can find them again!).

Cheers