Anyone know which wire powers the gauges on the opposite side of the firewall?

[bennylava]

All my gauges died after I got a little too happy with the power washer. I always try to be careful, but apparently the 87 truck didn't think I was careful enough. So I removed the cluster, and have confirmed it's got a good ground.

But when I checked the power wire with the multimeter, it's only showing millivolts, not volts. So that must be the problem, no power.

But I have no idea which wire that would be, on the other side of the firewall. I'm assuming it goes out through that big square bulkhead plug.

Any help would be greatly appreciated, thank you!

[kipps]

Factory wiring diagrams are located here. The 1987 diagrams are a funky style; consider using the nearly-identical 1988 diagrams instead. http://67-72chevytrucks.com/vboard/s...d.php?t=545416

[Pontiac1976]

Double check the grounds on firewall coming from bulkhead the Fuse box gauges fuse. and the + junction block on the firewall that gores to the bulkhead and the Alt., starter. The only other thing that might be leaking water bulkhead, a tar/rubber keep the water from the connector rust water short there. Any grounds that are removed should be checked put a light dab electric grease/oil just on the underside screw treads then tighten (make sure it's clean area size of a 50cent piece) You can use a paper/cardboard with hole ripped to around out to that size. Spray touch of rubber under coating 3-4mm thick. if you're going to clean with a power spray water often. this help keep the water from rusting grounds it will look all most factory should last around 1 year to 2 years depending how much cleaning and engine heat it gets.

[bennylava]

EDIT:

Well I managed to fix the problem by pulling the big square firewall plug and cleaning all the contacts on the outside. They looked fine on the inside, still had whatever dark goop paste used. The other side however, had turned green from corrosion that looked recent. Not real sure why that was a problem since they were all separated by plenty of plastic. But when it was gone, the gauges worked fine again.

[406 Q-ship]

Power for the instrument cluster comes from the fuse box on the inside of the cab. If you got really aggressive with the power washer you may have flooded the fuse block through the bulkhead connection. Check the fuses for blown fuses. BTW wire for any ignition power wire in a GM is always pink.

[bennylava]

Originally Posted by 406 Q-ship

Power for the instrument cluster comes from the fuse box on the inside of the cab. If you got really aggressive with the power washer you may have flooded the fuse block through the bulkhead connection. Check the fuses for blown fuses. BTW wire for any ignition power wire in a GM is always pink.

But where does that fuse box get it's power? Once I cleaned the outside of the big square bulkhead plug, all was well. You could tell it was new green corrosion. Some of the wiring diagrams in those manuals indicate that a few of the wires in that plug are indeed gauge cluster related.

The wires feeding into the plug look pretty vulnerable from the factory. I might have to make a square plastic cap that's held on by the same single bolt. Less concern about any water that way.

[406 Q-ship]

Originally Posted by bennylava

But where does that fuse box get it's power? Once I cleaned the outside of the big square bulkhead plug, all was well. You could tell it was new green corrosion. Some of the wiring diagrams in those manuals indicate that a few of the wires in that plug are indeed gauge cluster related.

The wires feeding into the plug look pretty vulnerable from the factory. I might have to make a square plastic cap that's held on by the same single bolt. Less concern about any water that way.

There is a main battery power that come from the Battery cable or starter positive lead that runs to the bulkhead connector and then it separates to the battery source for the fuse-box the other leg goes to the ignition switch and that is where the ignition power is distributed. From the ignition switch one of the wires powers the ignition coil this is unfused and a second wire goes the fuse-box where it is the ignition circuit fuses and your gauge hot in ignition wire will come from.

The bulkhead connector should have dia-electric or white lithium grease to prevent corrosion. That connector isn't vulnerable at all, GM has been using that system since the 1950's and most of the other manufactures have gone to a similar style of bulkhead connector.

[hatzie]

There are two main power wires. One from the bulkhead studs through the bulkhead plug to the fuse panel and ignition switch and one directly from the starter through a fusible link to the headlamp switch.
Both go through the bulkhead plug.

I'm not sure what the black GM factory goo is. I wish I knew... It was good stuff. If enough of it got rinsed away to allow corrosion I'd try to find some dielectric grease to splooge into the plugs.

[bennylava]

Originally Posted by 406 Q-ship

That connector isn't vulnerable at all, GM has been using that system since the 1950's and most of the other manufactures have gone to a similar style of bulkhead connector.

It's certainly vulnerable to washing your engine bay. You need to take care not to get any water on that plug. I found out the hard way. Granted it may be immune to water getting that high up just from driving.