What is this Ground - Near Instrument Cluster

Discussion in 'Sparky's corner' started by tminihan, Apr 29, 2020.

  1. tminihan

    tminihan 1970 GS455 Vert - Project

    The wire in the photo was connected (grounded) at the dash under the RHS instrument cluster mounting screw in my 70GS. The other end is just loose - ring connector. It's only about 12" long - could it be for the radio, tach housing or a/c controls?
    As far as I know everything is working fine. Thanks, Tom

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  2. LARRY70GS

    LARRY70GS a.k.a. "THE WIZARD"

    Where does the other end go? Maybe to the light switch. There is a ground that goes to the W/W switch to the headlight switch.
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  3. buick64203

    buick64203 Just plum crazy Staff Member

    Those are 2 different grounds- one for the wiper and another fir the headlight switch. This one is neither of them. Diednt look familiar to me. Some further investigation is needed.
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  4. tminihan

    tminihan 1970 GS455 Vert - Project

    Light switch and wipers are grounded and working properly. The other end of the wire was just hanging there. Based on the short length of 12" I figured it went to something near that right mounting tab. I put a new M&H dash harness in last summer, but I don't recall how the tach was grounded. I've never checked the tach for accuracy but I think it's in the ballpark at idle. Thanks, Tom
  5. 69GS&M21

    69GS&M21 Silver Level contributor

    So this mystery wire is part of the new harness that you installed? Could it be for an option that your car wasn't originally ordered with?
  6. tminihan

    tminihan 1970 GS455 Vert - Project

    Hi Jeff, the mystery wire was attached to the dash as shown in the photo when I received the car 10 years ago. I received the car fully disassembled for the most part. The instrument panel was in a box, wire attached to the dash. I did some troubleshooting yesterday. The tach was spot on at idle, well off the mark at higher engine speeds. I used my dremel to remove the light surface rust on the tach housing at the ground bus from the speedo and the other two attachment studs and re-installed - now reads almost spot on without the ground. So I am assuming a PO used this as a dedicated ground for the tach. What I haven't reasoned through in my mind though is that the tach lights worked fine which are grounded through the housing, so I assumed the whole unit well grounded. Thanks, Tom
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  7. 69GS&M21

    69GS&M21 Silver Level contributor

    I guess that is a good reminder that a ground may work, but it may not be a good ground if there is even just surface rust on it.

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