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Tach instrument cluster swap on '75 GMC

Discussion in 'Chevy Trucks' started by 75gmck25, Jul 9, 2003.

  1. 75gmck25

    75gmck25 Senior Member
    Messages: 119

    I have a '75 GMC K25 (350/TH350) that has the instrument cluster with gauges, but without a tach. I found a donor '74 3/4 ton Suburban (400/TH400) and it has a cluster with the tach option.

    I pulled the donor cluster, including tach wiring, but the engine was already gone and I'm not sure where the tach input was connected. Also, the donor truck was non-HEI and my truck has HEI.

    Do I just connect the cluster tach input to the tach connector on my HEI distributor? Is the input the same for HEI and non-HEI?
    Is there anything else I need to know about the cluster swap? It looks like it will just plug in to my '75 wiring, once I connect the tach wires to power, ground and distributor inputs.


  2. wyldman

    wyldman Member
    Messages: 3,265

    Welcome to Plowsite :waving:

    The cluster should bolt right up.According to the wiring diagrams,the cluster printed circuit is different,but the plug side wiring is the same.It should still work fine.I've done many cluster swaps and had no problem,only had to add the tach wiring.

    The tach wire plugs into the dist cap,right beside the Batt connector.It doesn't make a difference for HEI or non HEI,only where they connect.

    The tach wire should be the brown wire coming out of the little three prong inst cluster plug.The others are ground (black wire screws to dash bracing behind cluster,and power (pink\blk fed from fuse panel circuit 75,or any key on hot feed).
  3. snowjoker

    snowjoker Senior Member
    Messages: 283

    Welcome to Plowsite:waving: You will fing alot of nice informative members here. The wyldman being one of them;) will tell ya how to do it. Right Chris?:drinkup:
  4. 75gmck25

    75gmck25 Senior Member
    Messages: 119


    Thanks for the info. It verifies what I was able to figure out from the wiring diagrams and looking at the two trucks.
    I've been burned before when I didn't make sure it all fit before I took my truck apart and tried to make a swap. I just needed a sanity check before I started on the job. The tach instrument cluster was too good to pass up, and I was afraid it wouldn't be there if I waited too long.

  5. wyldman

    wyldman Member
    Messages: 3,265

    Thanks,I always try to help when I can. :drinkup: