Instrument lights not working - HELP!

[Troy P.]

I installed a new wiring harness in a 54 and everything works except the instrument lights in the dash. Thinking it might be the light switch and it's rheostat I tried two NOS and one repro switch. So I know its not the switch.

The commonality between all dash lights (except radio) is a grey wire which connects to the light switch rheostat.

Anyone know what the cause of this problem might be? If not how about a clue on how to troubleshoot?

[Roger W.]

Re: Instrument lights not working - HELP!

I just looked at the chassis wiring diagram for the 6 Cyl. (1953 thru 1955)
Do the headlights and other lights controlled by the headlight switch work? If they do, then the switch is probably getting the voltage necessary to power the instrument lamps.
The second thing to check is the fuse for the instrument panel lamps and clock lamp. Take the fuse out and check the resistance with a multimeter. It should be just about zero.
The third thing to check is the black ground wire for the instrument lamps. The diagram reads that it should be grounded to the instrument panel reinforcement. Fig. 1 Instrument Panel shows two black ground wires. One goes to the speedometer and the other goes to the clock. I don't know if the two shown black ground wires are typical for a 54.
Hope this gives you a few clues.

[Troy P.]

Re: Instrument lights not working - HELP!

Headlights, etc work. In this model there is no fuse for the panel lights. Not a big deal. Grounds are in place.

I have a feeling that the problem stems from the fact that the wiring harness came with plastic instrument bulb sockets and I replaced them with the original metal ones from the old wiring harness. Not sure why this would cause such an issue though.

Before reusing the original metal bulb holders I zinc plated them to improve their appearance. Also zinc plated the gauge cans. Is it possible that zinc is not a good conductor?

I believe the metal bulb holders provide a ground from the pins on the side of the bulb to the holder. Then the holder being plugged into the metal gauge housing then transfers the ground to the instrument panel reinforcement. Working at the bulb holder end of the circuit what would be the way to test? Check for power between the little copper contact that hits the bottom of the bulb and a good known ground?

Some of the bulb holders have two wires. Grey wire provides power and the other wire provides a signal telling the light to turn on or off. Turn signal arrows for example. Those bulbs work properly. Its just the background instrument lights that don't.

[Mark F.]

Re: Instrument lights not working - HELP!

Troy, according to this website (see Table below), zinc is a lot farther up the list of good conductors than I ever thought - so it doesn't look like that would be the issue. https://tampasteel.com/best-metals-conduct-electricity/

And I'm sure you probably already checked all of these, eh?
1. Do you have continuity on all the bulb filaments (stranger things have happened; with no fuse a voltage spike could do it)?
2. Is the rheostat set all the way to bright?
3. Does the contact tip on the bulb extend down far enough in the housing so it sits tightly against the "contact knob" on the end of the supply wire?

PS - how in the heck was it supposed to work with a plastic bulb holder?

Best to Worst – Which Metal is the Best Conductor of Electricity
(equally sized)

1	Silver (Pure)
2	Copper (Pure)
3	Gold (Pure)
4	Aluminum
5	Zinc
6	Nickel
7	Brass
8	Bronze
9	Iron (Pure)
10	Platinum
11	Steel (Carbonized)
12	Lead (Pure)
13	Stainless Steel

[Troy P.]

[Tony R.]

Re: Instrument lights not working - HELP!

I believe that sometimes when 'clear' zinc coating is done a corrosion resistant sealer is also applied. I think it is called a "passivation layer"? I don't know if this is conductive or not. Could this be an issue?

Another thought. How does the dash reinforcement end up providing ground? Is there a missing link there?

I have not gotten to this stage with mine.

[Roger W.]

Re: Instrument lights not working - HELP!

With the bulb out of the socket, very carefully touch the probe of a volt meter or tester light to the little contact in the center of the socket and the other lead to a known good ground. You could even run a test wire right from the negative post of the battery for your known good ground. If you get a voltage reading then you know that positive voltage is getting to the center contact. If you have voltage at the center contact, then install a bulb and try touching your test ground to the side of the bulb socket and or the little pins on the side of the bulb. If the lamp illuminates, when you touch the socket then you know that you have a ground problem. If the bulb does not illuminate, when you touch the ground to the socket, try to touch one of the little pins of the bulb. If the bulb illuminates then there is poor contact between the bulb pins and the socket. If the bulb illuminates when you touch the socket then try touching your test ground to the instrument panel reinforcement. If the lights work then you know that you have a bad ground.
Another thought is: How hard is it to replace one of your metal sockets with a plastic socket that came with the wiring harness, just to see if there is any improvement.

[Troy P.]

Re: Instrument lights not working - HELP!

I did the zinc plating myself. So no passivation layer.

There are threaded studs on the back of the dash reinforcement that are used to mount the gauges and speedo. A few of the ground wires also go on these studs or through an e-brake mounting bolt making the entire metal reinforcement a grounding plane.

[Troy P.]

Re: Instrument lights not working - HELP!

I will try that test procedure.

It wouldn't be too hard to change a socket. I have some of the copper tips left over that crimp on the end of the wire. Just inconvenient doing it laying on my back under the dash. But interesting idea.

One thought I had was the wiring harness might differ from stock somehow to accommodate use of the plastic bulb holders. But it looks like the plastic bulb holders are designed to act like the metal ones as far as electrical path. Otherwise everything is installed best I could follow the multiple wiring diagrams I researched. But I also have detailed under dash photo I've taken on low mileage unrestored 53-54 Corvettes to guide me. They sure came in handy.

[Richard M.]

Re: Instrument lights not working - HELP!

Does the '54 headlight switch have a small fuse like on the '56 switches? See left end of switch below. IIRC 3 Amp.

That small fuse is for the instrument lights on a '56. Not sure about '54.


1956 switch 1995082 - 1995072 similar with fuse.
P3100006.jpg

AIM_Sec12_Sht11.jpg

[Troy P.]

Re: Instrument lights not working - HELP!

No, the 53-55 6V switches do not have a fuse. Delco made a 6V switch with a fuse but it was for cars that had a dome light, not convertibles.

Testing between the red hot wire at the back of the switch and the grey instrument wire on the front (via rheostat) shows about 6 volts. This implies the light switch is passing the correct voltage to the instrument lights.

I made a 10 gauge primary wire 8' lead to reach to the battery neg terminal to create the optimum known ground. Testing at the bulb end revealed there is power to the copper tip on the end of the wire that the bulb contacts using this known ground BUT it is only 0.04 volts. Got the same result (0.03-0.05) with several bulb sockets as well as using the panel reinforcement ground rather than my known good ground.

With my limited electrical knowledge it seems to indicate the electrons are leaving the switch but getting lost on the way to the bulb sockets.

Any clues on what to do or test now?

[Mark F.]

Re: Instrument lights not working - HELP!

Troy,

Ignoring the voltage issue, do you have continuity from the gray wire contact point on the switch to each of the bulb socket contact points?

If all sockets show no continuity, then there must be a break, or a very bad connection somewhere along the line in the gray wire AFTER the switch, but before the sockets.

If all sockets show GOOD continuity, I (like you) am at a loss what's going on.

[Richard M.]

Re: Instrument lights not working - HELP!

Troy, some ideas inside your quote in Red..... Some of it is similar to Roger's ideas and Mark's continuity tests.

Rich

EDIT: After writing all of this below, I just thought of one more thing.... All of your bulbs are 6V bulbs, not 12V bulbs, correct?

No, the 53-55 6V switches do not have a fuse. Delco made a 6V switch with a fuse but it was for cars that had a dome light, not convertibles.

Ok I wasn't sure.

Testing between the red hot wire at the back of the switch and the grey instrument wire on the front (via rheostat) shows about 6 volts. This implies the light switch is passing the correct voltage to the instrument lights.

Actually no it isn't. I think based on placing your 2 probes on RED and Gray at the switch, the reason you get 6V is because the bulb filaments are then connecting to ground. A bulb filament is just a wire so it connects bulb tip to bulb base. This isn't a valid test and misled you.

Try this..... I numbered them so if you have questions you can refer back to the #.

1. Connect POS meter probe to RED at the HL switch, NEG meter probe to known Ground. Verify 6v there as a verification of valid meter reading via good Ground. If not, either RED isn't hot or bad ground. Get this working first. Once verified, then........

2. HL switch knob to 1st detent( Park/Tail/Inst = ON). Rotate HL knob fully CCW.(Inst lamps full bright)
Connect POS meter probe to GRAY at the switch, NEG meter probe to known Ground.

Test results?
3. If ~6V at Gray wire this means HL switch functional. Rotate HL knob CW then CCW and see if voltage drops and raises. If this works then HL switch is good.

4. If no voltage there then HL switch bad.(I doubt it as you tried 3 of them)

5. Try same test but now connect POS meter probe to a single Inst bulb socket gray wire tip. Make sure you still have NEG meter probe to known Ground. You should verify meter/ground again as in step 1. Rotate HL knob fully CCW.(Inst lamps full bright)

Test results?
6. If ~6V at bulb wire tip, the positive feed wire from HL switch Gray is good.

7. Reinstall bulb in holder and connect a ground wire to metal socket side or if plastic, the clip tangs. If it lights, you've now verified all wiring, except ground. Connect socket to metal cluster housing and it should light again. If not, the cluster housing is not grounded. Touch your ground wire to the BARE metal of the cluster housing and if it lights up, you're missing ground. I'm not sure how the harness gets it's ground but maybe a wire to the engine somewhere.

8. If no 6V at bulb wire tip, there is a open in the Gray wire circuit from HL switch inside harness. Try other bulb wire tips too. I doubt this is the case if your harness is new, but stranger things have happened.


I made a 10 gauge primary wire 8' lead to reach to the battery neg terminal to create the optimum known ground. Testing at the bulb end revealed there is power to the copper tip on the end of the wire that the bulb contacts using this known ground BUT it is only 0.04 volts. Got the same result (0.03-0.05) with several bulb sockets as well as using the panel reinforcement ground rather than my known good ground.

9.

0.04 V is not "power to the copper tip". That reading is basically a "no volts" reading. You need to measure ~6V there.

Did you touch your added ground wire to the reinforcement ground with any different results?

With my limited electrical knowledge it seems to indicate the electrons are leaving the switch but getting lost on the way to the bulb sockets.

Any clues on what to do or test now?

[Troy P.]

Re: Instrument lights not working - HELP!

More things to check. I'll let you know.

But I'm confused why the input/output test of the switch I thought I did is not correct. Just for yuks I will run that test again with the switch off/knob fully in and see what I get. With the switch off there should be no current leaving the switch via the grey instrument light wire. But with the switch at the first and second detent there should be about 6V and whatever amps. Correct?

[Richard M.]

Re: Instrument lights not working - HELP!

More things to check. I'll let you know.

But I'm confused why the input/output test of the switch I thought I did is not correct. Just for yuks I will run that test again with the switch off/knob fully in and see what I get. With the switch off there should be no current leaving the switch via the grey instrument light wire.


But with the switch at the first and second detent there should be about 6V and whatever amps. Correct?

Correct.... Measured between meter POS probe at Gray, and meter NEG probe at ground.

What you said was .....
Testing between the red hot wire at the back of the switch and the grey instrument wire on the front (via rheostat) shows about 6 volts.

This tells me your meter probes were on the RED and Gray.

If you meant to say...
Testing between the red hot wire and ground at the back of the switch and between the grey instrument wire and ground on the front (via rheostat) shows about 6 volts.

Then yes this would have told me your HL switch has correct voltage at HL switch output going to the lamps.

Maybe just a hiccup in description. Not sure but I was going by what I read. Sorry if I got it wrong.

ALSO... Not sure if you saw my edit in my previous post.....
"After writing all of this below, I just thought of one more thing.... All of your bulbs are 6V bulbs, not 12V bulbs, correct?"

Rich