Author Topic: Can we find some common ground?  (Read 142 times)

TA6.6Liter

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Can we find some common ground?
« on: November 08, 2018, 08:22:40 PM »
Okay, can we find some common ground?

Driving one night with the lights on, suddenly the tach dropped to zero, just the outside bulbs on the tach and speed all went dark. I didn't notice anything specific, just seemed to happen randomly.  A friend driving behind me told me that I also lost the tail lights, license plate lights and rear side markers, but not the brake lights or turn signals. Dash indicator lights worked.  Getting safely home, I tightened the ground wires on the trunk latch and checked the connector in the trunk.  All seemed fine.  The tach fuse under the dash was fine, but I replaced it anyway.  There is an inline fuse off the distributor on the tach side, which tested fine. The hazard lights, including dash indicators also worked. I gave up for the moment.  Then a day or two later I went at it again, but to my surprise everything was working, all lights and tach. Weird.  Several days later, again driving at night I didn't see it in time and hit a significant pothole. Same event, tach and lights went out.  Flipped on the hazards.  Then a few miles later, I drove over a rough train track and every thing came back on.

It seems obvious to me that I need to find a common ground, but all these are on different circuits as far as I can tell.  Any ideas out there?

NOT A TA

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Re: Can we find some common ground?
« Reply #1 on: November 08, 2018, 11:09:24 PM »
Body ground from fender to battery cable.
John Paige
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firebirdparts

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Re: Can we find some common ground?
« Reply #2 on: November 09, 2018, 07:06:07 AM »
If part of the lights on the cluster went out, then that problem has to be on the cluster printed circuit itself.  There's no 2nd chance for that to be somewhere else unless somebody cut a ribbon on the cluster and then ran a wire from it to some place.  that happened on the cluster itself.  The tach is grounded with the lights.  So really that problem is narrowed down to a single ribbon that is only about an inch long.

So I think it's two problems.  If I'm wrong, you're really not out anything. 

The park lights have 3 grounds, 2 in the front and 1 in the back.  Therefore, if all the park lights went out, the problem is on the power side.  Consider that.

If all the dash lights went out, then that's different, but that is the more familiar dash ground situation that is stickied.
« Last Edit: November 09, 2018, 07:09:29 AM by firebirdparts »
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Jack

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Re: Can we find some common ground?
« Reply #3 on: November 09, 2018, 11:07:57 AM »
The tach is grounded through the cluster housing, but some of the dash lights have separate grounds, I think the issue with the tach is the bonding strap might me loose and not making contact when jerked around, i.e., when you hit a pothole.




Regards, Jack

firebirdparts

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Re: Can we find some common ground?
« Reply #4 on: November 09, 2018, 11:28:08 AM »
The tach is grounded through the cluster housing, but some of the dash lights have separate grounds,

The ones that have separate grounds are the ones that are supposed to be off (brake and seatbelt).  They would be off before you hit the pothole.
I want to be like Paul Kenny when I grow up
Joe Bays
1977 Y82 4-speed (red interior)
1978 Skybird 350
1978 Redbird 305
1979 Redbird 301 4-speed
1992 Lincoln Mark VII LSC/SE (red)
1970 Datsun Pickup
1953 Chevy pickup (converted 4x4)
1988 T-bird Turbo Coupe

Re: Can we find some common ground?
« Reply #4 on: November 09, 2018, 11:28:08 AM »

TA6.6Liter

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Re: Can we find some common ground?
« Reply #5 on: November 13, 2018, 07:52:02 PM »
Body ground from fender to battery cable.

Is the body ground a  braided strap that goes from the bolt on the engine block were the negative battery cable is connected to the fender? It seems well attached at both ends.  I checked also the ground wire on each side of the radiator core to the wiring harness.  Both are snug.

TA6.6Liter

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Re: Can we find some common ground?
« Reply #6 on: November 13, 2018, 08:45:10 PM »
If part of the lights on the cluster went out, then that problem has to be on the cluster printed circuit itself...  There's no 2nd chance for that to be somewhere else unless somebody cut a ribbon on the cluster and then ran a wire from it to some place...  The tach is grounded with the lights.  So really that problem is narrowed down to a single ribbon that is only about an inch long.

So, that means pulling the cluster and looking for a broken wire?  The weird part is it is the same two bulbs each time; outer ones on the tach and speedometer.  The only other thing that comes to mind is when the restoration shop was finishing up, they were having problems with a battery drain.  They said it was fixed, but never explained what was wrong or how it was fixed.  I keep wondering if they did some extra engineering that is creating this situation. Don't want to take it back to them if I can avoid it. 

TA6.6Liter

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Re: Can we find some common ground?
« Reply #7 on: November 13, 2018, 08:48:20 PM »
The park lights have 3 grounds, 2 in the front and 1 in the back.  Therefore, if all the park lights went out, the problem is on the power side.  Consider that.

If all the dash lights went out, then that's different, but that is the more familiar dash ground situation that is stickied.

All the light grounds are snug; the two up front on the radiator core and the one at the trunk latch.  The fact that the tail lights went out, but the brakes, turn signals and hazard lights work adds some mystery.

Right, only two dash lights and the same ones at each event.

TA6.6Liter

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Re: Can we find some common ground?
« Reply #8 on: November 13, 2018, 08:49:34 PM »
I think the issue with the tach is the bonding strap might me loose and not making contact when jerked around, i.e., when you hit a pothole.

Where is the tach bonding strap located?

Re: Can we find some common ground?
« Reply #8 on: November 13, 2018, 08:49:34 PM »
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