Dash lights mess up my gauges - The I.P. Ground Story

[firebirdparts]

We used to have a sticky on this, and so here is the replacement.

The IP Ground on a Trans Am is to the dash frame to the driver's left, the short side.  The dash is plastic, so this frame is only grounded if the dash is bolted in.  There's supposed to be a bolt on each end of this frame.  If you are working on the dash, you are likely to remove the dash brace and you could lose ground of the other end, at the door, was loose.



The dash lights and the gauges are both grounded through this same path. If there is any resistance in this ground path, the lights will tend to put voltage on this circuit and the gauges will be affected.

[chief poncho]

Great sticky!  The IP isn't the best grounded.  I may run a ground strap to the chassis.

[pozarcar]

I installed a new dash gauge circuit "board".  When I got the gauge cluster reinstalled (bezel still off) and hooked up the battery, I got the "magic smoke" and discovered that the circuit to the ground pin on the dash harness plug (top left pin - black wire - on my 78) had melted. Would it be a bad IP ground that would cause this?

I had also converted my clock to quartz movement and reinstalled it.  Not sure I got the clock power wire put back right.  Is there a nut on the threaded end of the red power wire that goes inside the metal cluster housing, and then another nut on the outside securing the printed circuit, clock power wire and cluster housing all together?

[Wallington]

Sounds like an insulating washer or sleeve missing somewhere, live and grounding coming together . Any pics? Possibly pulled the gauges apart by now, also check the circuit board sheet, they have a habit of being the first to burn or mark since so flimsy, but this sounds more direct in the fixtures. Still 1978 style set? Wouldn't expect a missing earth would matter, it's just an extra. More the opposite.

[b_hill_86]

I’d think your clock conversion might be something to do with it. First I’d double check your new printed circuit against the old print circuit just to make sure they’re identical, and that you got the correct one but beyond that the only thing I can think of that would get battery power rather than ignition power is the clock. Did your cluster have the electromechanical clock that you replaced with quartz conversion? I’m going from memory, but no, I don’t believe there is another nut on that positive post for the clock, except the one on the exterior of the assembly.

[pozarcar]

Thanks for the help.  If there is an insulating washer that is supposed to go between the gauge cluster casing and the printed circuit somewhere, where does it go?

Also, if anyone has a pic of how the clock power wire stud looks when installed on the back of the cluster that would be helpful.

[b_hill_86]

I don’t know of any insulating washer off hand. Again, I don’t have my 77 cluster out and apart but I don’t remember anything like that. I do have a 79 cluster I recently took apart and there was nothing like that. What’s wrong with your old printed circuit?

[b_hill_86]

I think I’d remove the new printed circuit and look at the opposite side where the clock stud is and make sure there isn’t any copper exposed. Do the same with the old and compare.

Also, if you were to remove the nut holding the printed circuit on the clock power stud, does the stud move around if you wiggle it? I can see in your picture that that area is depressed and I’m starting to wonder if I remember they’re being a nut, then the printed circuit, then another nut, as I think you mentioned. I wonder if not having that nut may have cracked the back of the printed circuit, allowing the copper to make contact where it’s not supposed to.

[pozarcar]

I got it fixed.    I'm not sure which one of these did it (if any), but here is what I did.

- Did some repair on the printed circuit using some copper tape and a piece of copper wire on a really bendy circuit.

- Installed a insulating washer between the clock power stud and the metal cluster casing.

- Added a ground wire direct from the cluster casing to one of the steering column bolts.

I really appreciate the helpful advice.  I'm sure there are more problems to come!

[b_hill_86]

Nice! Glad you got it

[jbanna]

This might be too late, but you can buy new printed circuit boards for your instrument panel...I changed mine about 15 years ago so I didn't have to trace issues...