Swapping an 89 engine/700R4 for my early 86 engine/700R4. Original plan was to use the 89 harness and plug it into the firewall connector and swap out the chip. Noticed the wire colors at firewall do not match between the 2 harnesses. Thought about using the 86 harness, but noticed that it has 2 sensors in the front of the intake manifold and 89 only has 1. Any advice would be appreciated. I have the shop manual for my 86 so backup plan is to get an 89 manual (or get a few pages scanned) and compare the pins outs of the firewall connector.
I searched and did not find this information. If I missed it, please point me to the link. Thanks for taking time to read this and for responding with any advice.
Keith

 

You really really need the 89 wire diagram. The FSM elec BOOK is far too big to scan and copy that way....too many separate systems and even the complete drawing is HUGE...

its ALL the same though...some items have been relocated and IIRC the 86 had the temp sensors reversed on the block...all other L98s are the same. The intake had a cold start sensor next to the coolant temp sensor in front of the intake. The 89 again IIRC, had fuel enrichment and NO CS sensor as there is NO 9th injector or a fuel line to the rear of the fuel rail. Yr models that DO have the CS valve will have the steel line at the driver side rear rail....if that's the case here you can leave it off or unplugged. The ECM will not know the difference since it is not looking for a cold start sensor...it gets ALL its temp data from the other temp senders...

That firewall plug by the battery is ONLY for cabin/dash harness. The REAL goodies are not a plug-in harness section....that block you see on the firewall behind the dist is NOT a plug...just a big pass-thru rubber seal around the harness...
The harness is one long solid piece that enters by the evap box, rt behind the left engine valve cover, and goes directly to the fuse box, ECM and then SOME portions split off to the cluster and other portions of the dash.

Wish I could be more specific but my best advice would be to find an 89 FSM elect book to study and map out the color code differences and WHERE all the ends are.
Good luck!

 

If you need a shot of C100 from the 1989, I have a manual. I'll see what I can do about getting a pic of C100 scanned and posted for you.

 

Quick cell phone pic because scanner was not cooperating. Of course I'd get it up on here upside down. Just save image to your desktop, reopen image, and rotate left or right in whatever program you use so it is right side up.

 

Which intake are you using?

No need to swap harnesses if using '86 intake
The extra connector on the '86 harness is for the cold start switch
If you are using the '86 tune in your ECM then just install the CSI switch and connect it up.
And if using a '89 intake connector goes nowhere but you need a '89 tune in your ECM because the '89 intake
has no cold start injector

CSI switch is brass hex head unit shown to left of the CTS

 

Thanks for the help.
Based on the info posted, I think my new plan will be to use the 89 harness. I still need to take the top dash panel off and make sure the under dash connectors of the 89 harness mate up.
I am using the 89 intake, runners, and plenum, but with the 86 throttle body because the cable linkage connections were different.
Thanks again for taking time to respond and providing very useful information.

 

Thats a lot of work to swap that harness. I see no reason to do it.

 

Same ECM , no wiring changes needed

So as noted ; what are you doing about the cold start fueling with the cold start injector gone?

 

The ECM to engine harness does not have a connector. I call it the bulkhead feedthrough and it is permanently part of the harness. The wires go through it and then the opening is filled with some kind of sealer.

That is true for the C100 connector. I'm having a problem with my VSS right now and the wire color of one wire does change at the C100 connector.

Those wires are for the A.I.R. solenoids. In '86 they were two separate pieces. In 1989 GM changed to a one-piece unit. It's a lot cleaner physically and visually.

 

The quote being
" has 2 sensors in the front of the intake manifold ";
not two stray connectors hanging off the pass side harness.

Refer my pic above

 

vetteoz is right. I misinterpreted the original post. I made the assumption that it meant connectors instead of sensors. Many people do not know the names for things so what they write may not be what is actually there. I read too much into the post.

The '86 has a cold start injector thermo switch -- the '89 does not.

 

If you use the 86 throttlebody you must use the 86 plenum with 3 holes in the front. The triangle hole is required for the IAC to function that was changed in 89.