cpayne

I need to do this or buy one for my 87. Nice work!

Dictys

I did make a note, then lent it to someone and can't find it now.

However, we had a few issues with this and left this 3 pin plug till last and when I test fitted the harness I worked out the correct wires by running little jumpers to the oil pressure switch from the harness and checking the gauge on the dash. T

Then took the harness back out and wired in the old plug.

To fit the wires through the plug I pulled out the old connecters within the plug and desoldered them from the old bare wires.

Then from the plug side pushed a thin screwdriver through the plug and connected the wires on the new harness with tape and pulled the new wires back through the plug and then soldered on the old connectors.

Then pulled the wires back through thus pulling the connectors back within the plug.

Finally added a load or black sealant on the rear of the plug to stop liquid etc getting in the plug.

Harvey928

excellent advice thanks I will be doing the same in a few days.

17prospective buyer

I'd buy one... i pulled the engine bay harness off my 87 and it's pretty bad. EFI systems can go awry with low or high circuit voltage due to resistance in the wires, etc, i know how important it is.

What's the best way of testing an old one? What i had in mind was individually testing each wire's resistance (would take ages), then somehow finding out the exact length of that wire, and comparing your reading to a resistance chart that tells you what the resistance per foot is of a certain wire gauge. Obviously you would divide the total reading by how long in feet the wire is. The connectors on mine are all way too far gone for me to just comfortably put it back in the car when i put the motor in.

Did you create a diagram for the harness by following the 928 WSM diagrams for the harness? I was following the diagram but some of the ways they represent things on there are so confusing it's like you need to attend Porsche specific training on electronics to read them.

Dictys

I think you are referring to the Injector Harness rather than the Front Engine bay harness which is the one I replaced.

The injector harness is a little more involved as it runs through the firewall to the EZK and LH. It also has the bosch ECU connector on it and the weird rubber boot.

I had a old used harness which I disassembled and pegged out onto a board and used this for a template. This is the key. Then matched up wires using the wiring diagrams for my year. I didn't bother to test my old harness as the insulation had gone in places and it was very stiff. Once you cut open the center section in the harness it was amazing how many of the wires had perished.

I did another harness quite recently and it took about 4 - 5 hours start to finish, including testing.

I plan to do the Injector Harness at some point but for the moment I have just replaced the various connectors including the MAF connector with new connectors.

It is worth perserving with the wiring diagrams as once you get it, it is very easy to understand how everthing works. Alan's primer of the wiring diagram is very good.

17prospective buyer

Ok, maybe i will do what you did. Sourcing the connectors might be difficult but shouldn't be as bad as finding certain other 928 parts, as LH-Jet was used on alot of other cars. Couldn't you also use connectors from later Bosch EFI generations such as the ones used on 1990's-2000 BMW's? My Dad has a 2000 528i and i think it uses an advanced version of Motronic, but i was troubleshooting a misfiring problem for him and i noticed the connector for the MAF specifically was so similar to the 928 Bosch connectors, it has a different clip style that isn't as hard to release as the 928 ones.

Maybe i'll start by dissecting mine like you did. Thanks dictys!

Dictys

I purchased all the wires and connectors from vehicle wiring products and simtek in the uk, both have websites. I used the later junior power timer connectors where available.