Speedometer gauge lights not working

[NathanR]

Hi Team,

Recently had speedo rebuilt, works great. Just noticing this week the gauge lights are not working. All other gauges are illuminated. Tried twiddling with dimmer, no change.

Pulled speedo and removed bulbs. Lower bulb was fried. Replaced it, and it worked briefly. Now neither lower or upper are working.

Got out my multimeter and it doesn't appear there's any voltage on either wire, compared to gauge ground wire.

Wires visually look ok.

What else should i do?

[EC900]

The bulb socket wiring is fragile, especially so are the metal base sockets, (mine was very stubborn to get out, easy to yank the wire) keep in mind the metal base needed for ground, but the wire and contact inside could be loose from incidental tugging.

I don’t recall if both bulb sockets on the speedometer are metal base type with red plastic ferrule or the black plastic Bakelite.

If the bulb is larger style BA7 (?) they go in to the socket and hold with a spring tension, so it needed to twist set and lock in, maybe it’s loose, internally broken or not sufficient contact.

I’d still get some CRC QD electronics cleaner and spray the female terminals. Could be a ‘decades of air-cooled oil infused tarnish buildup’ problem.

Dimmer should control all the dash lighting, if others are adjusting then it’s not a dimmer issue.

For voltage test: The metal bulb socket base needs to be grounded to the gauge housing, they won’t light up (like the tiny 2w bayonet plastic bulb socket holders) if hanging outside of the gauge.

Worth noting too is to search PP for a dash lighting fused circuit upgrade for added protection.

[NathanR]

They are the metal with red plastic ferrule type.

I assume the bulb ground is through the metal holder and then the gauge can itself?

[EC900]

Originally Posted by NathanR

They are the metal with red plastic ferrule type.

I assume the bulb ground is through the metal holder and then the gauge can itself?

Yes, provided of course the Brown wires are connected to the spade on the gauge.

If you can get (new) bulb to light up (or not) outside of the gauge, try wiggling the socket to see if there’s some wire or connection issue there.

Here’s a similar generic socket from a previous Pelican post showing the spring that how the wire can separate from contact point :

[NathanR]

I will investigate further this weekend.

I wonder where the power leads originated? Do they all go back to the Headlight switch?

[NathanR]

Epilogue

The initial problem was a burnt out bulb, which I had identified and corrected prior to my original post. The subsequent issue turned out to be ground wires had become disconnected from gauge while I was fiddling with the bulbs. There are several ground wires that all tie together on a folding copper spade thingy that also connected to the gauge itself. That thingy had popped off the gauge.

Thanks EC900 for the suggestions!