Midnight89: After reading your comments about the problem, I would guess you have an electrical problem (just like you stated!). I have an 89 too and was having problems with the dash cluster. I cleaned the bulkhead connector and now all is well! The connector was a mess with black gunk! Here is how to do it:
1. Remove the body panel adjacent to the battery. This is easy but beware of some hidden screws.
2. Remove the battery and lay the leads aside. Look at the bulkhead just behind where the battery used to be. You will see multiple wires going to a big connector.
3. Using a 5/16 (I think) socket, remove the screw in the middle of the connector and the connector will just come apart from the bulkhead.
4. I stuffed some rags under the connector and sprayed the terminals with Gum Out. Be careful with this stuff as it removes paint. Use a tooth brush and clean both halves of the connectors until all the gunk is gone. Use compressed air to remove excess solvent and gunk.
5. I used Oxiguard (available at Home Depot) to coat the terminals prior to reinstalling the connector. This stuff coats the contacts and prevent corrosion and resistance problems. Use a pointed tool to coat each connector as this may take some time!

Doing this "cleanup" will not cost you much $$$ and it just may fix your problem. I have a scan tool and the temp reading on the scan tool does not match the dash reading. However, they are within 5 degrees of each other. Someone stated that the dash temp reading and the ECM reading come from different sensors. The cluster temp reading electrical circuit goes thru the main bulkhead cluster described above. This may be the sorce of your problem! Good luck and keep trying!
SAM

 

Sounds like something I should do. Haven't had a close look at mine and quite a while.

Sam, did you disconnect the wire from the block or just clean them in place.


Jake

 

Jake: If you remove the 5/16 screw (in the middle of the plastic connector and you have to look closely to see this screw) the outer half of the connector just pulls away from the stationary part of the connector. Inside of this are the "female" parts of each each electrical connection. With the slack in the wires, you can move the connector with wires attached and give 'em a good cleaning with a solvent and a tooth brush. I used Gum Out. You need to clean the stationary half of the connector too. I wish I had taken a picture of the black gunk inside this connector as I would not have believed what I found! I also like the Oxiguard on the electical joints. It is easy but takes some time.
SAM

 

Thanks Sam Lam...sounds like I've got a Saturday project ahead of me. I think it would also be wise for me to pick up a laser temperature gauge to get a better idea of exactly how hot the coolant is getting.

Thanks ALL, I'll keep you guys posted!

 

Well, I just finished cleaning mine, went down right after my last post here. Two 10 mm screws and the entire unit/block was unbolted. I moved it up so I could get to the nut easier and get a really close look at the connections.

Wasn't too bad to get to, since I'm familar with how to get the battery out without too much fuss. Because of my ground effects kit, I have to remove the inner fender liner/shield and the cruise control servo, then it slides out from the front.

My power connector wasn't too bad at all. I mixed up some baking soda and water and poured it on the connector to see if any battery acid had botton on the connections, but it didn't fizzle at all.

I did find that three of the five burn off relay wires were showing wire. Don't know how the insulation had disappeared on those three wires, but it was a good thing they hadn't touched each other.

Thanks for the tip; nothing like checking to be sure.

Jake

 

I've posted several times about the bulkhead connection-BUT, I'm only quoting Gordon Killebrew-most problems with our digital displays can be traced to water in the bulkead connection. BUT, the black gunk in there according to Gordon is an anti corrosion grease-he says leave it there-what you're looking for is a greenish or whiteish looking area which indicates water, he says to just blow it out then seal the top and sides of the connection after reinstall, also the drip tube from the cowling may be directed right at the connection-if it is-redirect it away.

 

Good Info.

Last night, when I was checking my 12V power block behind the battery, I noticed a brownish/black grease-feeling substance (when I was repairing the MAF burn-off relay connection wires. I'd seen it before on other connectors (headlight relay connectors) and I figured it was to prevent moisture and corrosion, so I left it alone.

The power block and the wires connected to it didn't have any sign of corrosion, either visually or with the baking soda check, but there was NONE of the brownish/black, grease-feeling substance on it. The grease has the same consistency as wheel bearing grease, heavy gooey stuff.

I wonder if it can be purchased at an auto parts stores.

I also saw the bulk head connector you mentioned. I didn't know about it being the prime source of dash problems though. Thanks for that. I noticed it was sealed with a sort of a tar like substance which I figured was to keep out moisture too.

Maybe sometime in the future I'll tear into bulkhead connector to have a look see. On a car that's going on 20 years old I'll bet the connections will show their age.

Appreciate the info.

Jake

 

Really unnecessary with the '89 - harness was changed and the problematic ground was re-routed - it now runs with/through the ECM harness on the opposite side of the firewall and there are no connectors to clean. Bulkhead connector is headlights and ignition circuits. Use the '89 Electrical Supplement for the pinouts as they are different then the Shop Manual.

 

I've got an 86, so I guess that doesn't apply to me, right?

Jake

 

Right, for '86, cluster ground should be at B1 in the bulkhead connector. For '89, it's a direct pass through bundled up with the ECM harness. The only cluster problem I've experienced with any of the wires in the bulkhead connector was an inaccurate Voltimeter and actually the problem was in the ignition switch - high resistance across the contacts. Some electrical contact cleaner solved it.

 

Now we're in an area that I know very little about. My Shop Manual may have the specifics on B1 at the back of the book that's tell me the wire color, etc. I'm thinking that splicing in an additional ground wire to B1 would create a better ground to the dash. What do you think?

So, to clean the contacts I'd need to disassemble the ignition switch. I've never researched how to go about that, but cleaning them sounds like a good idea..

Occasionally, when I start the engine my dash is dark but I can see the numbers RPM, Oil Pressure, MPH, etc. are functioning normally. If I shut down the engine and restart, the dash illuminates as it should. I believe it's ground related.

Any advice will be appreciated.

Jake

 

Jake, you might want to run an additional ground wire from the ambient sensor (per Gordon Killebrew), on the inside of the vette-drivers side where the main wiring harness goes thru the bulkhead you will see an object attached to it about the diameter of a dime and about a half inch thick-this is the ambient sensor-it has two wires attached to it-but I'm at work until 6PM and I can't remember what color one you splice into and ground-if you want to do this just email me at r.w.lambert@att.net and I'll look it up when I get home and email you.
Gordon recommends this-even if it doesn't fix the problem he says to leave it grounded. There's also another ground wire on the drivers side door post that sometimes get corroded-hope this helps.

 

Jake

If your dash is working but faint then the back light bulbs are not turning on. These dash clusters are notorious for cold solder joints. In the top left corner of your display is a photocell. It controls the brightness or dimness of your bulbs. The next time your cluster is extremely dim tap lightly around the photocell. If your lights come on you need to resolder the photocell to the board.

I found the following link to be of great use.

http://batee.com/corvette/

To test the photo cell during the daytime, place your finger over the hole and see if the lights get dimmer. If they do the photocell is working correctly.