Instrument bulbs not burning

[clemsontiger]

So I'm in the process of putting the dash back together and I figure I'll go ahead and change any bulbs that are burnt out before I do when I notice NONE are burning. :-/ Most of you know this is a new project for me and my guess is they haven't burned the whole time I've owned the car. Well, I pulled one out of the Speedo and it was bad, so I replaced it w/a new one...nothing. I then start to work on the center guage cluster...the first one I pull there is good, but I replace it anyway...still nothing. I guess the point is, their not all bad, but none of them work. Any ideas? Headlight switch maybe? Anyway to test...to put direct power to them to see if they light? Any thoughts would be greatly appreciated!

[radi8]

Mine didn't work either- was the dimmer in the headlight switch.
I used a DMM to find the "ground" side of one bulb socket and applied +12V to the other pin...they all lit up. I figure there was power to the switch because the headlights worked, but nothing coming out for the dash lights.

[sfallison]

Most likely, it's your ground to the instrument panel, or the dimmer.

[6880 Mike]

Originally Posted by sfallison

...it's your ground to the instrument panel...

Yep. Nothing is going to work without the main harness ground.

IP fuse good?

[clemsontiger]

Could it still be the ground if the headlights work (the headlight alert light on the center console burns as well)? I'm thinking it's more like the dimmer part of the switch too, but I'd like to know how to check the ground and/or where its should be grounded to if that could indeed be the problem.

I think the IP fuse is good because the other lights in the dash work (brake warning and bright light warning)...although come to think of it, the turn signals don't work either. Any help there?

[clemsontiger]

Could this have something to do with the LS1 engine change, as in, could it bee that there is supposed to be a ground on the alternator (I'm pretty sure that hasn't been hooked back up yet) or elsewhere under the hood that could be causing this?

[72LS1Vette]

Originally Posted by clemsontiger

Could it still be the ground if the headlights work (the headlight alert light on the center console burns as well)? I'm thinking it's more like the dimmer part of the switch too, but I'd like to know how to check the ground and/or where its should be grounded to if that could indeed be the problem.

I think the IP fuse is good because the other lights in the dash work (brake warning and bright light warning)...although come to think of it, the turn signals don't work either. Any help there?

The first thing to check is the fuse. The gauge lights have their own fuse - it's a short 5A one near the bottom center of the fuse panel, at least on a 72. The brake warning lights are on a different circuit. The turn signals are a whole different problem. Could be anything from bad grounds to a bad turn signal switch.

Edit: looking back at your original post - are your bulbs connected with a single grey wire? If so, you have to plug them in to the sockets to test them or else they won't have a ground connection.



Rick B.

[clemsontiger]

Originally Posted by 72LS1Vette

The first thing to check is the fuse. The gauge lights have their own fuse - it's a short 5A one near the bottom center of the fuse panel, at least on a 72. The brake warning lights are on a different circuit. The turn signals are a whole different problem. Could be anything from bad grounds to a bad turn signal switch.

Edit: looking back at your original post - are your bulbs connected with a single grey wire? If so, you have to plug them in to the sockets to test them or else they won't have a ground connection.



Rick B.

Well, with another set of eyes I actually found the 5a fuse to be bad and got the console guage lights to burn...no such luck on the speedo/tach. Do they have their own fuse?

[6880 Mike]

Originally Posted by clemsontiger

...found the 5a fuse to be bad and got the console guage lights to burn...no such luck on the speedo/tach. Do they have their own fuse?...

Speedo and tach lights are tell-tales only. Turn signals, hi beams, ebrake, etc. The dash harness must be grounded. Speedo and tach each have their separate grounds on the rear of the housings.

[clemsontiger]

Originally Posted by 6880 Mike

Speedo and tach lights are tell-tales only. Turn signals, hi beams, ebrake, etc. The dash harness must be grounded. Speedo and tach each have their separate grounds on the rear of the housings.

"tell-tales only"? It just hit me that the turn signals are prob not working because one of the front lights is burnt out...so maybe that's my issue there. The speedo and tach housing have to be grounded I'm assuming, becase the brake warning in the tach assembly and the high beam warning in the speedo both work.

I guess it could be that all 8 lights are burned out, but that seems very unlikely, although the only one I've taken out to look at was indeed. So there is no seperate fuse for the speedo and tach lights?

[72LS1Vette]

The speedo and tach backlighting is on the same circuit as the console gauges, so you may just be missing ground on the speedo/tach. You can connect a wire to a ground point and reach up underneath to touch it to one of the housings to see if the lights come on.



Rick B.