Want to start off first, by saying Hi to everyone. I have the greatest admiration and respect for all of you, as I have been reading posts for months and picking up all kinds of advise along the way.
My problem is with my '81. Recently removed the dash, console, etc. to replace the heater core, and re-dye dash. Went to put everything back together, hook up battery, turn on ignition, and center gauge circuit smokes. Car would start, but had no voltmeter, oil pressure function of the gauges. Everything else seemed to work until I turned on the headlights and both turn signal indicators came on. Left the car sit overnight, tried to start it the next day, car wouldn't crank over. Took the alt. out had it tested it was OK, took the starter out, tested it, it was bad, got a new one, and re-charged the battery. Got a new printed circuit, checked and cleaned up all the ground connection points (except for the rear). Put everything back together, turn the key and the printed circuit smokes again, car starts but now runs like timing is way off, and smokes like the dickens.
Prior to all of this the car ran fine, and all the gauges worked, (except the oil temp, which was not hooked up-no sending unit)
I did do a continuity check for the ground to dash panel (with out the battery in the car) and with the neg probe at the ground, I touched each of the contacts on the center gauge plug, and was getting continuity. Is that supposed to be?
I am by no means electrically inclined, and could really use some help here. I have no idea where to start. Thanks.

 

you plugged something in wrong, twice. Take a few pics and post them, we will see if we can figure it out

 

Thanks Sixfooter for your reply.
Was off taking out the dash again and took some pictures, but can not attach them to this post. Some help would be appreciated.

 

Here's how to post pictures.

http://forums.corvetteforum.com/show....php?t=1336867

 

Thanks Duke94 for your help. Here's one of the imagines.

 

Two others, the second one is the old one.

 

Did you just change the circuit board? I just went through this. Make sure that the porcelain resisters do not have a nut between them and the metal pan, they face contact side up, then the nut goes on.

I had a nut under one side of the resistors and instantly fried my new circuit board. All the posts that have a resistor on them have voltage supplied to them. If those posts aren't insulated from the metal pan, you will supply the grounded pan with 12v releasing smoke from the electrical system.

 

Looks like the ground from the oil pressure gauge fryed. I would also check headlight switch

 

I made notes and drawing as to how the gauges were assembled and even made note of were each nut was before disassembly, but I will check on that when I go to remove printed circuit. Thanks for your suggestion. (The first picture was the new printed circuit that smoked, just after I'd pulled out gauge cluster. The second was also the new circuit with the plug removed. The third picture was the old circuit that smoked when I had first reinstalled gauge cluster).
I checked the grounding of the light switch for continuity and it was OK. Is there another way to check to see if the light switch is bad? The lights and marker lights did work last I knew. Any suggestions would be greatly appreciated.
I did also have a gas leak on the carb.,and wound up removing it to tighten up a loose screw, and reinstalled it (no more leak), reconnected all vacuum connections (only 3 to deal with, plus elect. choke).
What would cause the car to run so rough at idle? It's almost like timing is way off or the spark plugs aren't getting good spark. Something in the distributor wiring? Could this be all related to the gauge cluster/ printed circuit problem?
Prior to this the car was running fine.

 

81 was the first year for the computer controlled carburetor. This computer controlled both the mixture and the timing.

You have an ALDL (Assembly Line Diagnostic Link) connector under your ashtray.

Check all the wires and everything around your carburetor and distributor.

If your car is running rough, it is also something aggravating the computer, not just your gauge cluster. You have a short straight to ground somewhere. A connector backwards or something.

You can download the parts manual online for free at

http://corvettec3.ca/partsman.htm Not as good as a wiring diagram but might help.

Good Luck!

Rd

 

After looking up the engine ID, I found that it was a '78 truck motor, hence this is no computer control. Thanks for the advise though. I do have the shop manual which has the wiring schematics (very intimidating) which I have studied for quite awhile, and being electrically challenged, it's a bit confusing and overwhelming to me. I also have the assembly manual, which doesn't seem to be much help.

I did have to re-do the 2 wire plug on the alt. as the smaller brown wire broke off of the plastic connection. Had to put female spades on both (soldered and shrink tubing) It's the red and brown connection on terminals 1 & 2. The brown wire was very brittle. Could this be the culprit for the rough idle, or printed circuit burn out?

 

Step back a take a deep breath. Lets start from the being. I can figure out most of these problems. Its a little tougher when I am not there.

Back to the begining. What exactly did you remove when you did the core? Center cluster? Console? Dash? Any wiring what so ever?

Lets go to the board. Point out the burn? is it on ALL printed circuits or on one strand? if its on one strand which one? If its on one strand follow it back to the plug. Identify the wire on the plug that attaches to the burned strand on the board. That is the wire thats would be your problem. If its muliple strands chances are the two wires causing the burn are making contact somewhere up line. Did you pinch any or the harness?

Are you blowing fuses?? Check the fuses? If you are not blowing fuses the strands in the circuit board are burning and acting as fuses. So that you maybe understand. A fuse will blow if its capaciity is exceeded. But it the exceed level on a fuse is higher then the exceed level of the circuit board strand the strand will fry.

You have an engine from a 1978? What controls the choke if there is no computer or is there a computer?

What distributor do you have??? HEI? Is the coil in the top of the distributor? Do you have wires coming from the bottom of it and the top??

One more thing. Leave the center board unplugged. will the car start? Does everything work if the center cluster is not plugged in. Example the lights...signals etc. If not whats not working with the board unplugged.

Jim

 

Would I be correct in assuming that all black wires in the electrical system are negative (ground) Only? If so, I had thought of splicing in a black wire to the two black wires on the center gauge cluster plug, and running it directly to the pillar post ground (under dash on left side). Any thoughts on this? Also, is there any way, or reason to check the volt meter to make sure it is still working?
Oil pressure sending unit was put in with teflon tape, I have since removed the tape, thinking it was preventing the sender from grounding.

 

Took another look at your board pictures. See the tan wire on the plug....follow the print on the circuit...goes to the the center guage....what guage is that in your car? The circuit looks fryed after that guage.

follow the tan wire back from that plug...where does it go? Any breaks? Any pinch???

Jim

 

They are all ground and should have no power on them. So if you checked the blacks with a test light you should get no light. I wouldn't start splicing things. this is not a "no ground" issue.

Jim

 

funny you mention the oil pressure switch. Looked at my diagram. Granted its for an 82 but it looks like the Tan is for the signal for the oil pressure switch. but refers to a computer. If you no longer have a computer how is the tan spliced into the new configuration??

Jim

 

You say the block is a '78 truck block. That has nothing to do with the computer controls. The computer controls the distributor and the carb, not the block. Do you have idle adjustment screws on the carb? Are there two wire harnesses that connect to it? If it has the electrical connections you are still running the '81 carb. If you don't have the electrical connections on the carb, does your distributor have vacuum advance?

 

Thanks jdp6000 for piping in. To answer your first question, when I replaced the heater core, I took out the dash, shift console, center gauge cluster, speedo/tach cluster, and did not remove any wires, meerly unplugged.

Only one strand has burned, it runs to the pink/black connection on the plug (second prong on the left from the top). The burned strand runs to the left at the top, down around the two idiot lights, back towards the center and then down between the volt meter, and the oil pressure. It's the left strand in the picture between volt and oil pres. It "y's" to the left to the volt, and towards the right to the oil pres.

No fuses are blowing as I have check the all Again.

The carb is a Holley with electric choke and the red wire for the choke runs to one of the ign. plug ins on the fuse panel.

The coil is on top, so I'm assuming it is HEI dist. It has 3 wires that plug in under the square overhang off the dist. cap.

I have not tried to start the car without the center gauge cluster disconnected. Would it be OK to try and start the car with the dash and all out?

 

Funny you mentioned the tan wire, checked the tan wire last night and it runs directly to the oil pressure sending unit. It had been cut off and a gray wire had been added that runs directly to the oil pres. sender. Bubba?

 

You can start it with out the dash stuff hooked up. Try it. Takes the board that frys out of the equation.

Let me know what happens. Any weired problems.

today is a tough day to help figure this out....mothers day and all.

I'll try checking from time to time.

Jim