Strange Electrical Issue affecting Gauges

It's haunted.

It's not a bad alternator, nor is it a bad ignition switch.  It looks like you have a loose ground to the gauges.

Or the +12 volt feed from the ignition switch to the gauge cluster has a loose connection.  Either way, it's gauge power or ground related.

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If I were given to wagering, I think I’d place my bet with Gordon.

The grounds for the gauges are usually daisy-chained and led to one connection point. The trick can be finding that point. I think the ground wire for my gauges disappears into the wiring harness.

If you can’t find the ground connection under the dash (it can be difficult finding anything under the dash), try tracing the ground lead from the battery out of the frunk. That is usually connected to the frame somewhere near the steering box, under the car at the bottom end of the steering column - where grease, road grime, and corrosion like to hang out. On my car, a number of other ground wires are led to that point. It might be a good idea to undo that and clean everything up there.

I’m guessing it’s not the engine warming up that’s reawakening your gauges, but the vibration of the whole business that comes with rolling down the road.

Also, is it the speedo that dies when you hit the blinkers or the tach? In most of our cars, the speedo is mechanical, but the tach is electric.

+1 on a faulty ground.

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@Dutch posted:

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...Also I noticed that when I use the turn signal (left and right) it seems to affect the gauges i.e. the speedo goes down to zero and none of the turn signals work....

Another thought. This could be the key to all of these issues.

Something may have loosened up in the turn signal switch, causing it to move and tug on some wiring every time it's thrown.

Only the stalk itself should move, not the housing it's mounted in.

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Wow, all great replies and Gordon I think your suggestions are what I will use to track down this issue first. I also think now that ther is an errant ground as I have seen some questionable junctions that need to be cleaned up, i.e. a ground wire just wrapped around a spade lug....Outside of all of your great suggestions which I will follow up on, the innitial feedback regarding my speedy being haunted if all else fails will require me finding a good medium! Thanks as always everyone, this is a most awesome crowd of supportive members. Hopefully I will have a positive update soon!

Mitch I do plan to raise the  speedy off the ground to check all the grounds underneath the pan as well. Excellent feedback, thanks!

All of the builders find their dash grounds in different places so it’s hard to offer advice on where to look, but each gauge can has a 1/4” electrical tab or a ground lug somewhere on the gauge can with (typically) a green (American style) or brown (German style) wire attached that goes from gauge to gauge and then to a metal frame member up behind the dash.  Find it on one gauge and follow it to the others and chassis ground.

There are always problems with grounds on fiberglass cars ,

Would it be smart for fiberglass body makers to run a ground cable in the wet fiberglass,

maybe one for front lights , one for rear lights and one for the dashboard,

Just a thought…..

Naaah…….   That would make too much sense.

It’s not a big deal the way it is now, though.  The frame ground points are plentiful and pretty good. We’ve seen more issues at the light or gauge ends over the years.  Usually they’re just loose.

2 things come to mind here when reading your post.

1) there are several internal grounds inside the gauges (as well as other wiring) that you cannot see, so even if all visible grounds look good, you may still have an internal gauge short.

2) looking a little deeper into the short or ground issue and your exact symptoms, you oil temperature sender is a resistor to ground that is almost open  when cold and provides a better and better ground as it gets hot.  Thus, I'd look at that circuit also.  If your gauge grounds are shorted to that sender somehow it would provide little to no ground when you first started up and then as you warmed up it would provide better ground.  This "idea #2" is NOT something I have experienced, but it would explain the correlation between time and functionality and is the only thing I can think of that would not have a ground at first and then have one as it warmed up.  That sensor is easy enough to unplug at the motor, and you can also hold the end to the engine case and force a full ground at any time to test this...

@chines1 posted:

2 things come to mind here when reading your post.

1) there are several internal grounds inside the gauges (as well as other wiring) that you cannot see, so even if all visible grounds look good, you may still have an internal gauge short.

2) looking a little deeper into the short or ground issue and your exact symptoms, you oil temperature sender is a resistor to ground that is almost open  when cold and provides a better and better ground as it gets hot.  Thus, I'd look at that circuit also.  If your gauge grounds are shorted to that sender somehow it would provide little to no ground when you first started up and then as you warmed up it would provide better ground.  This "idea #2" is NOT something I have experienced, but it would explain the correlation between time and functionality and is the only thing I can think of that would not have a ground at first and then have one as it warmed up.  That sensor is easy enough to unplug at the motor, and you can also hold the end to the engine case and force a full ground at any time to test this...

@chines1 - I think you have struck gold on this idea and it makes sense to test it out as you suggest. As I mentioned, all the gauges do come up after the car warms up so your suggestion regarding the oil gauge being a resistor to ground makes sense. The other thing I did not mention is that I have 2 temperature sensors, the in-dash one show just the geen to red zones and the second one bolted onto the dash below the main gauges shows actual temperature in degrees. I may try to disconnect each one, one at a time to see if there is any relationship to one or the other causing the issue. Thank you for your suggestion and I am on it! Will let you know the outcome asap.

@Gordon Nichols posted:

Naaah…….   That would make too much sense.

It’s not a big deal the way it is now, though.  The frame ground points are plentiful and pretty good. We’ve seen more issues at the light or gauge ends over the years.  Usually they’re just loose.

Gordon - The ones I thought were loose because they were wire wrapped around another ground lug were actually soldered on, however I am also going to clean those up and make better connection with newly stripped wire and a single spade lug for both wires.

@imperial posted:

There are always problems with grounds on fiberglass cars ,

Would it be smart for fiberglass body makers to run a ground cable in the wet fiberglass,

maybe one for front lights , one for rear lights and one for the dashboard,

Just a thought…..

Not a bad idea @imperial but Gordon is correct, there are plenty of frame grounds I can chase down once I lift the speedy.

@Gordon Nichols posted:

All of the builders find their dash grounds in different places so it’s hard to offer advice on where to look, but each gauge can has a 1/4” electrical tab or a ground lug somewhere on the gauge can with (typically) a green (American style) or brown (German style) wire attached that goes from gauge to gauge and then to a metal frame member up behind the dash.  Find it on one gauge and follow it to the others and chassis ground.

Will do and though it may take a while to chase them down from each guage, I know where they terminate on the frame, thanks!

@Sacto Mitch posted:

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Another thought. This could be the key to all of these issues.

Something may have loosened up in the turn signal switch, causing it to move and tug on some wiring every time it's thrown.

Only the stalk itself should move, not the housing it's mounted in.

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Thanks Mitch, I did check the stalk and it is very secure, no movement.

@Dutch  Please don't create new threads for the same topic. It makes the topic hard to follow.

For those following:  Here is a link to the new thread and I will lock this one.
https://www.speedsterowners.co...ffecting-gauges-cont

thanks
-=theron