brdd

Can someone confirm for me what fuse is for the gray wire dash lights. 72 small block.

Wire harness is original and unwrapped. Lights will work if I connect separate power supply and ground. I tried a different switch and that did not power the lights. Headlights do work with switch on.

I think the dash lights are powered by the little fuse on the bottom of the fuse bank. Is this correct?

If the issue might be in the wire harness connecting the headlight switch, which wire on the 72 switch harness might power the dash lights?

As always, thanks for any ideas.

Dan in Minnesota

Peterbuilt

The dash light fuse gets power from the tail lamp fuse so check that fuse.
The ground for the center gauges connects from the black wire on the temp gauge to just above the bottom of the drivers side dash on the 'A' pillar (shown as 'harn gd').




72 schematic:


http://www.vetteprojects.com/bmv/mis...tte%201972.pdf

65GGvert

There are two fuses that must be good to get dash lights. One is the instr fuse and the other is the tail light fuse. The voltage passes through the tail lamp fuse and then the instr so that if you blow a tail light fuse it will be apparent from inside the car. Check both with a meter, they may look good but be loose from the metal cap. You may also have some corrosion on the metal clips in the fuse box.

bruiser

I believe the dark green wire on the headlight switch goes to the instrument lamp fuse. Then the grey wire goes from the fuse to all the light bulbs.

brdd

Thanks for the assistance. Time to go look at this stuff. Thanks again.

I always learn something when I post a question here.

DUB

100% correct.

The dash lights or instrument /gauge lights is controlled by the headlight switch...(the dark green wire)....which when the headlight switch **** is pulled....it supplies power to the 1/2 size glass fuse in the fuse panel....which then powers up the light bulbs.

SO..only one fuse protects and makes the instrument/gauge light work. And it is the same all the way up to 1982...except for the fuse design change.

DUB

65GGvert

That's true after it leaves the headlight switch, however the brown lead to the lights (other than headlights) is fused by the taillamp fuse which if blown will cut off voltage to the switch rheostat and thus the instrument lamps

brdd

I tried a new headlight switch. No go, so I don't think it is the existing switch. The half-fuse is changed and an new one is in place. No go on that either. I changed out the taillamp fuse too.

If I had someone to take it to I would do that, but no one in my town that I know of will work on stuff like this. Cold weather is not far off and I really don't want to put that dash back together without the dash lights working. I may store the car this winter with the dash apart.

As stated earlier, the bulbs all work when I connect them to a 12 volt power supply. A DC voltmeter reads nothing on them when attached.

When I get home today I will connect the 12 volt supply to the green wire to see if it will power the lights.

65GGvert

Use a volt meter or test light. Check for voltage on both sides of the small fuse. Post back what you get and I'll tell you which direction to go for the fix.
Just to be sure, you know that you won't have voltage on the dash lights (or the small fuse) unless the park or headlights are on AND the dimmer rheostat is rotated away from full down brightness?

brdd

I checked voltage across the little mini fuse at the bottom of the fuse block. No voltage registers whether key is on or off. I tested another fuse in the block and it registered 12.4 volts with key on.

Thanks for any advice..........
Dan in Minnesota

DUB

Dan,
The mini fuse for your gauge lights does NOT require your key to be on. The headlight switch **** DOES need to be pulled to get this small fuse to get power.

If your headlight switch can be accessed....when you pull the ****...check the voltage at the dark green wire that is in the connector that is attached to your headlight switch....and you also have to make sure the **** is turned so the gauge lights will be at their brightest. I have had brand new headlight switches NOT work the gauge lights.

DUB

65GGvert

Do this just for me: Measure both sides of the tail lamp fuse and post back what you get. ( or just look and tell me if the tail lights come on when you pull the headlight switch to park or run.
If your tail lights work and you don't have voltage on the small fuse, your problem is either the rheostat in the new switch or a bad connection to the switch. If your green wire is connected properly to the light switch, you should have 12v on it. If you don't I think you're looking at a bad dimmer in the switch. You can jump 12v to the green wire and see if your lights come on. You never said whether you rotated the dimmer throughout it's range to see if the dash lights flickered off and on. Try that too

brdd

Hello again

Tail Lights and signal lights work.

I'm getting some voltage now because the gauge lights come on but are VERY dim. This is with a fully charged new battery.


The dash harness has never been out but the engine harness has been changed. Is it possible that some damage to the connection occurred when the engine harness was plugged into the firewall area?

65GGvert

Does rotating the dash dimmer left and right CHANGE the brightness any at all? I'm having trouble getting you to tell me if the dimmer has any affect. The voltage on the small fuse will vary with the rotation, that's what changes the brightness of the instr lamps.

65GGvert

Rereading your original post you said adding 12v and ground made them work. Do one at a time to see if it's a ground problem or a voltage problem. If you don't get 12v on the small fuse with setting at full bright, it's a problem with the voltage that comes off the rheostat via the green wire.

brdd

When the dimmer is turned the brightness on the gauges goes from bad to non-existent. When fully brightened you can just barely see the lights behind the gauges.

brdd

Any and all of the gray wire bulbs will light up well when I connect a separate, independent 12 volt power supply directly to the metal around the bulb and a ground. Nice and bright then.

Raphiki

Sounds like a bad ground. Either loose or corroded.

brdd

Will do this tomorrow.

I have a "car guy" coming on Sunday afternoon for a while. He has done other projects on this car so I think he will be able to solve this mystery for me. He is taking pity on me!

brdd

The culprit is the ground connections: they are not up to par. When we experiment with other ground connections we get varying qualities of brightness from none to very bright. We haven't decided what way to go here but I have come to the conclusion that, when it comes to ground in a circuit, more is better.

We will play around with the speedo and tach grounds and experiment more until the dash is properly lit.

Thanks for all the input here.......one more part of the puzzle being conquered.............