Speedo acting up w lights on

[Cdnone1]

The speedometer on my 82 SC just started acting up when I turn my lights on.
With the lights off everything is fine, but when I turn the lights on the speedo jumps all around and the speedo lights flicker.
Any one have any experiences with this? I thought it might be the ground but before I start tearing it apart I thought I'd ask
Thanks
Steve

[Cdnone1]

Bump

[tcar]

Guessing here.

Ground problem?

[Hellraiser]

Had this problem too, found out it was the ideal opportunity to strip and
clean the wiring loom and install xenon

[tcar]

Don't know about xenon.

What wattage in your headlights?

The sucro relay kit would probably help:

New Headlight Relay Kit available from Pelican

[Cdnone1]

Everything nut the speedo works fine. Even the speedo works fine when the lights are off. there is no pulsing anywhere but in the speedo. Headlights cabin light and dash lights all work fine. It's just the speedo that goes crazy and it just started. I haven't touched the electrical in almost a year.
Steve

[dshepp806]

What was touched in the "electrical" one year ago?

best,

[Cdnone1]

I've had the gauges out to rebuild the speedo (9 months ago) I installed a new radio and thats about it
Steve

[lfot]

I had a similar issue, but not with the speedo, but the tach. After doing a thorough check of wiring and all, it turned out to be a failing alternator. Mine is also an '82 SC. It was the original alternator with the separate voltage regulator. Changed it out for a Carrera alternator/regulator combo and I've not had a problem since.

Do you notice the lights subtly pulsing, very slowly and almost unnoticeable? Do your interior lights dim when you turn on your lights?

[dshepp806]

Originally Posted by lfot

I had a similar issue, but not with the speedo, but the tach. After doing a thorough check of wiring and all, it turned out to be a failing alternator. Mine is also an '82 SC. It was the original alternator with the separate voltage regulator. Changed it out for a Carrera alternator/regulator combo and I've not had a problem since.

Do you notice the lights subtly pulsing, very slowly and almost unnoticeable? Do your interior lights dim when you turn on your lights?

This is the most common,..had my Passport programmed to read voltage and started to notice spiking above it's limit (no Tach malfunction, although it's quite common). It only took a couple of alarms for me to get this baby in for an ALT/REG changeout (I envisioned failed DME, as a result). Found it to be THE original ALT/REG from '89..this happened just last year....Maybe not something related,..but have you monitored the voltage to ensure you're not getting spiking ?

Otherwise,..I'd check the connections at back of instrument first...you may have something failing within the instrument...when you say it was "rebuilt", what exactly was done and why?

Best,

[dshepp806]

Understood that one still would seek the relation of the headlamps to the speedo..........

Could it be, in fact, "load" related, as those babies (lights) pull a respectable degree of current...?

Either the supply side (whichever component that may be) is bad, or you have an intrusive wire somewhere,..or the instrument, itself, is failing.

Just some thoughts...

[Cdnone1]

I've had the speedo out several times. First to change the gauge face and second to replace the odometer gear.
It's strange that nothing else surges except the speedo and it's both the speedo lights and needle that jump around. I have had Alts go before and it's usually the tack that acts up but this is just the one gauge and only when I turn the lights on
steve

[Cdnone1]

I've had the speedo out several times. First to change the gauge face and second to replace the odometer gear.
It's strange that nothing else surges except the speedo and it's both the speedo lights and needle that jump around. I have had Alts go before and it's usually the tack that acts up but this is just the one gauge and only when I turn the lights on
steve

[lfot]

Originally Posted by Cdnone1

I've had the speedo out several times. First to change the gauge face and second to replace the odometer gear.
It's strange that nothing else surges except the speedo and it's both the speedo lights and needle that jump around. I have had Alts go before and it's usually the tack that acts up but this is just the one gauge and only when I turn the lights on
steve

Maybe it's a bad connection with the light inside the speedo? Or possibly a bad bulb?
The assumption is that it's caused by the surge from the outside lights, but at the same time the gauge lights go on.
Maybe try pulling the bulbs from the speedo for a test run.

[midlife]

Have you checked the ground connection to the speedo?
When I first bought my car the tach would change when the lights were turned on. It turned out to be a bad ground connection to the back of the tach.

[Cdnone1]

Thanks everybody.
I've been pouring over the electrical diagrams trying to figure out how to approach this.
I can not find a connection from the headlight switch that only goes to the speedo. If anyone knows of one please chime in. I figure if it was a weak or pulsing signal from the switch it would effect the lights on all the gauges not just the speedo and would not effect the needles movement.
It's kind of weird
I think I'll start with the ground on the speedo.
Steve

[Hellraiser]

If you check out the car at night, can you see the
dash lights lightly lit when your lights are off?

[dshepp806]

On the guage rebuild, was the electrolytic capacitor (s) changed out?

Best,

[Cdnone1]

I will check the lights tonight. No the capacitor was not changed out but it is not connected to the gauge lights is it?
Steve

[colorado930]

Cdone1,

I had a similar problem with my 88 930 and my research indicated that the voltage regulator or alternator could be the cause.

I sent my alternator to be rebuilt and am in the process of putting it back in the car as soon as I get an assist on the wire connections from someone with an electrical diagram in the forum. I am anxious to see if this cured the problem. Will advise further, once I complete the alternator installation.

Regards,

Vincent
88 - 930
Colorado Springs, CO