In 1981 the C3 Corvette was a victim of the industry migration to computer controls. Today, those 1981 Corvettes are now tipping the 40 year mark and many of the electronic components are beginning to fail or, new owners are rebuilding these cars and eliminating the electronic control modules. Compounding the age failure of ancient electronics is the fact that at some point, most of these cars have had someone get into the console and make a mess out of the wiring trying to install a stereo. Because of this and a variety of direct to metal factory grounds, there are a number of parasitic battery drain issues to resolve. For these reasons, I decided to start another thread to discuss electronic and wiring related issues on the 1981 corvette.

I have a 1981 with a crate motor in it. I have removed the original intake and carburetor and installed an Eddlebrock performer intake, a FiTech fuel injection system, and an MSD pro billet distributor, locked and phased to allow the FiTech to control the timing. With tis complete, the only task left for this computer to perform is the transmission lock up on the TH350 transmission. It is now my intention to remove the ECU completely and live without the lockup.

While tracing some of Bubba's wiring, I found an unterminated yellow wire in the center console, cut off clean behind the stereo. I traced it back to an electronic module behind the passengers seat, in the jack compartment.my question is.... what are these two electronic components? Are they necessary?

I read somewhere that one of them was for the windshield wipers. I just cant imagine how they could have been working with this wire disconnected, if in fact that is what that wire leads to.

Can anyone help me solve the mystery?

 

alarm is behind pas seat forward of storage
compartment

 

excellent. thank you! is the wiper delay module also back there?

i have never seen, used or attempted to use the alarm since i have owned this car. is there any danger or potential problem created by removing all of that apparatus in that compartment?

 

There is a thread here that deals strictly with
wiring diagrams for all the years.
Just specify the year you want and the specific
diagram for your car will be emailed to you.
sorry I don't have the link but other members here will.

good luck

 

In all of the removal of computer wiring and Fitech install, i have encountered a problem i have never seen. I was hoping someone here may be able to offer some insight and guidance
I started with a 1981 corvette with a crate motor but a stock intake. The car ran pretty good, but it was having issues with cold starts and a head gasket. I replaced the head gaskets, milled the heads, etc. I replaced the intake with an Eddlebrock Performer and picked up a Fitech GoEFI which i have installed on a couple of other cars in the past. I have added short tube block hugger headers and new exhaust as well as a high torque mini starter.

I can start the car, it will run and run well. the moment you touch the brake peddle, the car dies completely. i know what you are thinking... vacuum ... nope, that was my first thought. thats not it. it is more of an electrical failure. it is almost as if the ignition is just killed. if i wait a few minutes, it will start again.

1 - Fitech installed
2 - ECM unhooked
3 - All wires to the old intake and carb have been cut and capped

My only thought is that some of the wires cut in the removal of the ECM / Intake wiring or the old alarm system are to blame.

Is there an ignition relay i am missing that could be to blame?


Any thoughts or insights on this mystery would be appreciated.

 

2 things on brake pedal
stop light
tranny lockup disconnect which also cuts cruise control

 

Look up Papawanna, he will send you a copy of the wiring diagram.

 

ok... that may make sense... thats where ill start. thank you

 

will do thank you

 

Does it die every time you hit the brake? Even after restartung it?

 

So i hooked the ECM back up and wouldn't you know it, the issues stopped. So now the question is why? Is there some connection between the lock up/cruise that could kill the ignition?

 

yes.... and you don't need to really push in far enough to activate the brake... just the slightest tap of the brake kills it.

 

So the cruise control is causing this then. The FSM should list the diagram for this. I would be going over that circuit end to end to figure out why.

 

i have one more mystery to solve for this project. that is the tachometer mystery.
the factory set up had a white wire coming off of the tach that had a tach filter. that plugged in to a singular connection on the firewall that was relatively separate from the main wiring harness that had all the ECM wires. As you can imagine, having changed to a standard distributor and coil, i no longer have a tach signal. but i cannot for the life of me figure out which wire that would be. i ran a jumper from the wire the tach filter was plugged in to, and got nothing.

Even with the wiring diagram, it is difficult to discern the color and striping of some of these 40 year old wires.

 

The white tachometer wire should now go to the negative terminal on the ignition coil. However read the paper work that came with the new coil/distributor concerning tachometer hook up for any precautions. Sometimes aftermarket stuff doesn't play nicely with OEM stuff.

 

thanks for that... Would that be the same wire the old tach filter was connected to on the old HEI? i think i have tried jumping from that wire to the coil already and didnt get a signal.... but hell ill try it again... wouldnt be the first time i made a mistake.

basically, im just trying to restore the tach signal to my stock tachometer at this point, after having removed the HEI and the old Quadrajet, and original intake.

 

Well try it again if it doesn't work try bypassing the filter and see if that helps. Does your new Fi tech system have a tach output. You could try that if all else fails.

 

the FiTech does have a tack reading on the hand held. So I can see rpm there. But I really want my tach to work.

 

I was thinking a dedicated output just for the factory tachometer.

 

No, the FiTech also relies on a connection to the coil to get it's engine speed reading.