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Old 04-20-2008, 12:53 PM   #1
nate99
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Default 1981 Engine Wiring Harness Question

So as I dig in to my new project 1981, I'm finding all kinds of fun surprises. I have a rat's nest of wires running all over my engine compartment with many of them dangling unconnected. The car does run, but it has apparently been "bubba'd" more than a few times to get it that way.

My plan is to swap out the stock engine for a crate engine, and when I do that, I was planning on getting a new distributor and carb, so I would like to go ahead and get rid of the Computer Control stuff altogether.

So my question is, if I am going to get a replacement engine harness, should I just go with a 1980 version that would have provisions for a normal HEI distributor and could be run with an Edelbrock or Holley carb?

I'm guessing 1980, but I'm not sure other than the distributor and carb changes what else I might be up against after the crate engine is intalled.

Thanks.
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Old 04-20-2008, 01:19 PM   #2
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or maybe even earlier like 75 to keep it simple. tach feed would be one concern.
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Old 04-20-2008, 03:27 PM   #3
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I'm doing a similar conversion on my '81. I hadn't considered using an older harness so it will be interesting to see what others think.
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Old 04-20-2008, 03:31 PM   #4
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Originally Posted by A88FXRS View Post
or maybe even earlier like 75 to keep it simple. tach feed would be one concern.


There are also other items that would concern me. Probably your best bet is to loook over several wiring diagrams and figure out which year will suit you best, depending on which accessories you plan to leave on.

Your vacuum hoses are going to be a bit of an adventure as well. I redid all of mine on my stock 81 and I swear that there were miles of them. Each had a function too and you're going to have to figure out which ones you can do without.
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Old 04-20-2008, 04:31 PM   #5
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There are also other items that would concern me. Probably your best bet is to loook over several wiring diagrams and figure out which year will suit you best, depending on which accessories you plan to leave on.

Your vacuum hoses are going to be a bit of an adventure as well. I redid all of mine on my stock 81 and I swear that there were miles of them. Each had a function too and you're going to have to figure out which ones you can do without.
Oh yeah, there are vacuum hoses going everywhere.

Looking at wiring diagrams makes my head hurt, but, I guess I need to get a hold of one for an '81 to see what all was supposed to be there in the first place, because there is no telling what is or is not there now. I have a Haynes manual, it should be in there.

To give you an idea of how bad it is, there was even one of those Crane Ignition boosters (smaller than an MSD box) screwed on to the firewall not connected to anything, and the main alternator wire has a butt connector splice about six inches off of the back.

What year was the first for HEI distributors?
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Old 04-20-2008, 06:33 PM   #6
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Some high(low)lights:

What is that red thing with the (disconnected) vacuum lines running from it?

Click the image to open in full size.

The aforementioned Crane thing

Click the image to open in full size.

Alternator madness:

Click the image to open in full size.

Lastly, what is this switchbelow and outboard of the master cylinder?

Click the image to open in full size.
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Old 04-20-2008, 06:51 PM   #7
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My pieced together 1974 car has 1980 wire harnesses; interior, engine and headlight w/ a dash and cluster from a 1982. All works good but it has some splices in it. I had purchased a used 81 interior/gauge cluster harness for it but didn't use it...too many open connections to the ECM.
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Old 04-21-2008, 12:00 AM   #8
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That switch below you're master cylinder is for the cruise control as far i as know.
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Old 04-21-2008, 02:21 AM   #9
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i also have an 81. most of the wiring is computer related. if u plan on installing a different carb,dizzy,trans than i suggest removing the computer ( some forum members will tell you to keep it original and not do this ) trace all the wires back from the computer . by the way they come out in one big harness . then you have a blank canvas. on mine the only wire i had to pluck out of the bundle was the aircon control wire. here is a series of pics from start to finish. did it all by myself at home completed in 6 weeks.

Click the image to open in full size.

Click the image to open in full size.

Click the image to open in full size.

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Old 04-21-2008, 07:00 AM   #10
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Originally Posted by gingerbreadman1977 View Post
i also have an 81. most of the wiring is computer related. if u plan on installing a different carb,dizzy,trans than i suggest removing the computer ( some forum members will tell you to keep it original and not do this ) trace all the wires back from the computer . by the way they come out in one big harness . then you have a blank canvas. on mine the only wire i had to pluck out of the bundle was the aircon control wire. here is a series of pics from start to finish. did it all by myself at home completed in 6 weeks.

That looks to be exactly what I want to do. What type of harness did you use for the install??
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Old 04-21-2008, 07:25 AM   #11
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That looks to be exactly what I want to do. What type of harness did you use for the install??
i just used what was there.i had no need to get a new harness cause my car had no bubba action and everything bar the ciggy lighter worked. as i said ...once you yank out that big bulky computer and harness thats attached to it you will only have the necessites left. all those loose plugs going nowhere in your engine bay are from that harness , 95 % of them anyway. there is so much crap running to that stock carb,exhaust,dizzy ,tranny.

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Old 04-21-2008, 09:07 AM   #12
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i just used what was there.i had no need to get a new harness cause my car had no bubba action and everything bar the ciggy lighter worked. as i said ...once you yank out that big bulky computer and harness thats attached to it you will only have the necessites left. all those loose plugs going nowhere in your engine bay are from that harness , 95 % of them anyway. there is so much crap running to that stock carb,exhaust,dizzy ,tranny.

You were luckier that I. I am seriously skeptical of what is left in there. I might start with that method, see what is left and then ask around with some of the earlier model guys to see what they have that is comparable.

Love those valve covers btw...

Thanks.
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Old 04-21-2008, 09:13 AM   #13
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That switch below you're master cylinder is for the cruise control as far i as know.
Thanks, that helps. Once I get to it, I am on a mission to clean out the engine compartment.

My car will not be a highway cruiser any time in the near future, so my whole cruise setup will be going in a box in the attic.
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Old 04-22-2008, 12:11 AM   #14
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yeah i put my cruise away as well. i did like to use it before but now with this fresh motor and the gearing i have i dont need it any more either. i doubt i will ever put it on again at all to be honest but at least it is always around if i want to go back to a cruiser. bye bye to all that smog stuff and all the vacum and wires that go to that. bye bye to all the emission stuff on that carb and manifold. bye bye to that ugly block huggers with the smog pipes coming off the top. once you get into it and just start rebuilding it all just falls into place.
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Old 04-22-2008, 07:14 AM   #15
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I did the same. I removed the original motor and installed a crate motor. Your engine harness is the same as a 1980. The harness with all the connectors is the computer. I removed the computer on mine and that cleaned up alot of the mess. Your 81 engine harness will work with a regular distributor.

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Old 04-22-2008, 08:23 AM   #16
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Good reading, guys.

So here is the dumb question or two....what was the function of the ECM and associated harness in the 81 actually doing?

Does it make a difference if car is auto versus 4 speed?


I have a 76 and going to look at an 81 that has "some" work done to it and now wondering if I should be concerned or not if the ECM is not connected or present.
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Old 04-22-2008, 08:53 AM   #17
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From what I have gathered, the ECM controlled something in the carb metering, something in the distributor, and the torque converter lockup.

There may be more, but others will have to chime in.
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Old 04-23-2008, 12:52 PM   #18
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Good reading, guys.

So here is the dumb question or two....what was the function of the ECM and associated harness in the 81 actually doing?

Does it make a difference if car is auto versus 4 speed?


I have a 76 and going to look at an 81 that has "some" work done to it and now wondering if I should be concerned or not if the ECM is not connected or present.
The computer in the 81s controlled a few things, but the major one is that it would adjust the mixture at the carb, primarily based on input from the O2 sensor, by cycling the metering rods at different rates.

The other important thing that the CCC did was to control the advance in the distributor. If your system wasn't working, no advance at any RPM.

The computer also electrically locked up the torque converter on AT cars so I suppose that's wy it mattered if it was 4 sp or AT.

As for why you should check if the system is functional, if it isn't working properly, the carb will default to full rich mixture and the distributor will default to zero advance (so it will stay at whatever baseline advance you set it to). It won't run well, won't have good power and burn tons of gas.

When working well, it is a pretty good system. When not working, you might as well replace the carb and distributor and set up your lockup to work on a switch.
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Old 04-23-2008, 01:52 PM   #19
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The computer in the 81s controlled a few things, but the major one is that it would adjust the mixture at the carb, primarily based on input from the O2 sensor, by cycling the metering rods at different rates.

The other important thing that the CCC did was to control the advance in the distributor. If your system wasn't working, no advance at any RPM.

The computer also electrically locked up the torque converter on AT cars so I suppose that's wy it mattered if it was 4 sp or AT.

As for why you should check if the system is functional, if it isn't working properly, the carb will default to full rich mixture and the distributor will default to zero advance (so it will stay at whatever baseline advance you set it to). It won't run well, won't have good power and burn tons of gas.

When working well, it is a pretty good system. When not working, you might as well replace the carb and distributor and set up your lockup to work on a switch.
This must be why my exhaust will make your eyes water, and why the previous owner had trouble getting the timing just right.

A previous owner installed headers with no provision for O2 sensors, so I think that I am probably S.O.L. until I scrap the whole setup, which was my plan anyway. I guess that I'll probably do that before the paint/interior now...
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Old 04-23-2008, 02:02 PM   #20
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Originally Posted by CA-Legal-Vette View Post
The computer in the 81s controlled a few things, but the major one is that it would adjust the mixture at the carb, primarily based on input from the O2 sensor, by cycling the metering rods at different rates.

The other important thing that the CCC did was to control the advance in the distributor. If your system wasn't working, no advance at any RPM.

The computer also electrically locked up the torque converter on AT cars so I suppose that's wy it mattered if it was 4 sp or AT.

As for why you should check if the system is functional, if it isn't working properly, the carb will default to full rich mixture and the distributor will default to zero advance (so it will stay at whatever baseline advance you set it to). It won't run well, won't have good power and burn tons of gas.

When working well, it is a pretty good system. When not working, you might as well replace the carb and distributor and set up your lockup to work on a switch.


I did this and now my problem is, how can I tell which is on or off to lockup the converter???
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Old 04-23-2008, 02:02 PM
 
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