Welcome to the Corvette Forums at the Corvette Action Center!

C4 wiring...


Gone but not forgotten
Jan 30, 2001
Hermosa Beach, CA
1987 Z51 Silver Coupe
I don't even know how to phrase this...

As some of you are aware, I've been experiencing (battling) electrical gremlins for some time now: :eyerole
  • I have an intermittent no-start condition. :mad
  • The overdrive sometime works, sometimes doesn't. Today it worked again as I drove to Burbank to Guldstrand's shop! :confused
  • My backup lights quit working about six months ago. :(
  • After I had to "Bubba" the wires into the distributor, I'm sure there are more pigtails/wiring that are dried, cracked and/or broken.

As well as the wiring being old and deteriorating, the vacuum lines are probably in no better shape; I am aware of a few small cracks already. :(

My question I guess is: what is involved, and how involved should I get with replacing the wiring (how far should I go)? There are individual front and a rear harnesses, correct?

Replacing the wiring is a fairly extreme way of fixing your problems.

Unless you have had some kind of abusive condition under the hood (fire, vandalism, engine exchange/mixed up parts) there should be no reason to replace the entire harness.

Your problems could be with the components and not the wires. You might also have a simple grounding problem. Although there is nothing simple about finding a bad ground, it is a single source of many different problems.

Give me more details on the no-start problem.

Chris McDonald said:
Give me more details on the no-start problem.

Chris, all I can say about the no-start bug-a-boo is the it is intermittent :mad. Lately it has been happening more when it's hot, or rather, when it is at operating temperature (200 +/-), whereas in the past it would occur when I got off the graveyard shift at work and it was cold and damp. :confused

  • The starter is the most recent replacement.
  • The VATS has been bypassed with the piece available from Mid America.
  • The only sound I get when I turn the key is a faint click from behind the driver information panel, so I replaced the starter enable relay.
  • I have an aftermarket alarm installed, but the starter kill function has been disabled.
  • It fires right up when you push start it; it's a DN 4+3 so at least I can pop the clutch to start it if I leave it on a grade.
  • :eyerole

As to the wiring question, the only reason I mentioned the harness was if the pigtails, connections, and clips are drying, cracking and falling off, how far back up the wiring should I go to repair what is bad so far?

Thanks for your interest in my pesky little problem. :gap

What about the actual starter switch on the column just above the brake pedal. Have you replaced or adjusted it?

I would hook a test light up to the input and output side of the switch to see if there is power one either side during the failure.

Changing the terminal ends is a common procedure anymore as the harness gets old and cracked. You can purchase the terminal ends from G.M. or some of the local discount chains. Autozone has a wide assortment.

I suggest soldering the connection and using heat shrink to keep the elements out. That is not a bad idea to replace as you see yours deteriating.

Oh yeah, don't forget to check the starter saftey switch on the top of the clutch pedal. If it is bad, or worn it won't let a solid flow of current through the relay to the starter. Either that switch or the actual ignition switch down on the lower part of the column may be what you are hearing click. There is really nothing else down there.

Don't give up on it. Let us know what you find.
Electrons sometimes suck...... Hole theory

You see the brit's had part of the theory correct.When you let the smoke out of the wiring it dosen't work. My expansion on the theory...
Your car knows when you have money and it sucks that out of your wallet to start current flowing again!

That being said

PepBoys is now starting to carry a HUGH selection of replacement connectors on pigtails, with a big catalog to order from. All you have to do is learn how to solder. The catalog ( if I remember correctly) had a selection of the de-pinning tools
so you could just change the plastic shells, however those were a bit pricey. The wiring harness itself is probably OK as far as the wires go.. it's just the brittle nylon ends of the lock tangs that are broken.
The other thing is ( if you go the pigtail/solder route ) get plenty of CLEAR shrink tube to put over some of the marginal wires when you cut the connection.

Id try looking into you ignition system bud check your coil and starter (Coils are cheap) rotor cap distributor and vac lines all around

I replaced mine with some yellow ones from my race shop and did my ignition fairly cheaply plus I gained to 26 MPG on the highway
MSD 6AL - 349$
Blaster 2 coil 100$
Wires 8.5 MSD 100$
Plugs 35$

All I did was this to my Ignition system and I have NEVER had a problem of any kind (Plus the added HP aint to bad either )

As for the OD thing mine was acting up to (4+3 Standard)
So I ripped off the console and found 2 wires connecting the button on the shifter I pulled them both and replaced and I have never had a problem since take a look =)
Don't give up on it. Let us know what you find.
Don't worry Chris, I'm certainly not going to give up on it at this point. :L

Your car knows when you have money and it sucks that out of your wallet to start current flowing again!
:L Good one vigman! :L
(I do have the Pep Boys Catalog, I check it out.)

...found 2 wires connecting the button on the shifter
BigRed, they moved the switch sometime in '85 from the console to the shifter knob.

...check your coil
:L It's been replaced twice within the last three weeks. I think the diagnosis was incorrect when they replaced it both times; I found a loose (broken locking tab) on the pink/white striped wire going to the "BATT" connection on the distributor the last time it died on me. We "bubba'd" it and it started right up. But that was only the loss of spark part, the "no-start" condition still exists. :eyerole

Thanks for the help guys, keep it coming. :upthumbs


Engine Not Grounded to the Uniframe
From start of production of the 1984 to about December 12th, 1987 ('88 model) the ground strap was attached to the uniframe along with the black wire coming from the negative battery cable by a 10mm headed screw. Sometimes the ground terminals do not make good contact to the uniframe. Early in the '88 model (about December 12th) the negative battery small black wire had a ground screw of its own going to the uniframe. The braided strap had another 10mm headed screw forward 15mm on the uniframe attaching it to the uniframe. This created a good backup ground system (engine to uniframe).
Usually when the engine to uniframe ground is bad, the dash displays a low voltage and may turn on the caution light when the voltage reaches 11.5 volts DC or less. On 1986-87 cars when this ground path was bad sometimes a no-start VATS problem was noticed.
Many times after the transmission was removed and reinstalled a poor engine ground occurred. The top left bellhousing bolt and terminals did not make good contact to the engine.

He then goes on to troubleshoot various conditions.

I think it's all coming together now; if only I could figure out where to start! :L

Dude I know about the move from the console to the Stick shift mine has it on the stick also if you go underneath the console there you will see the stick and the wire going up the shifter to the Selector switch (Also on the stick) take that wire Off

they short out ALL the time and keep removing it untill you reach the main harness then (I cut it there) replace with some good flexible 12 Gauge
Here's an update on some of it...

I finally got around to pulling the digital cluster back out, and tearing into it, after reading Gordon Killebrew's book on the subject.

I followed the instructions on removing the upper cicuit board from the lower circuit board, I cleaned the contacts where there wiring harness plugs into the unit, the contacts where the upper and lower boards plug together, and I replaced a couple of the bulbs and sockets while I was in there.

I reassembled the whole thing and re-installed it in the dash. WAIT, Murphy's Law strikes again! The bulbs that I took the effort to replace, were bad. Instead of removing the entire unit again, I simply replaced those bulbs with the ones I had removed previously. They worked.

I then turned on the ignition, and Voila!, no flickering. :D Better yet (but I'm not getting my hopes up or holding my breath), the overdrive now seems to be functioning properly. :confused

One thing at a time, eh? ;)

Re: Here's an update on some of it...

1987 Z51 said:
...but I'm not getting my hopes up or holding my breath), the overdrive now seems to be functioning properly.

Nope! That wasn't it, but I just discovered another relay that might be the cause. We'll see tomorrow. :eyerole

You have to really wonder how many feet, yards,...........miles there are of wires in that car. I bet you could rewire six 66 coupes for one C4.

We had a crazy problem in the 90 where it kept blowing the turn signal fuse. Not right away, but after driving it. Anyway, after tracing miles of wire I had to diconnect the back up feed source and run fresh. So far, that has fixed it. Who would have thought that the back up circuit was intermingled with the turn signals?
Re: O/D switch costs...

nyernga said:
...a new O/D switch ($145.00 from mid america)

:eek I have a feeling were not talking about the same overdrive switch in this case. When I replaced the shifter-mounted overdrive selector switch on mine a few years ago, it only cost me around $40-45 if I remember correctly (And I'm too lazy to dig out the paperwork for it right now. You knew that I'd have every receipt for everything I've ever spent on this Corvette didn't ya?;))

I just found out about the overdrive relay, located next to the fuel pump relay, in the engine compartment; and yes, I did know about the switches on the transmission itself. The second gear detent switch is a possibility.

It's really weird(er) lately; sometimes it will stay engaged when it is supposed to be engaged, other times it simply refuses to function at all. Never though, does it not dis-engage when I command it to do so. :eyerole

It's a good thing I like puzzles. :L


Corvette Forums

Not a member of the Corvette Action Center?  Join now!  It's free!

Help support the Corvette Action Center!

Supporting Vendors


MacMulkin Chevrolet - The Second Largest Corvette Dealer in the Country!

Advertise with the Corvette Action Center!

Double Your Chances!

Our Partners

Top Bottom