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installing tachometer

mike maule

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I bought a tachometer for my 79 620. Took out gauge cluster to install it and have questions. I found a yellow with red tracer taped up in main harness with a female bullet, tachometer has male on that color wire. The tachometer also has a black wire with a female spade. On the back of the speedometer(from the tach I bought)  is a small box with a red that goes to speedometer, a yellow that goes to circuit board, and the yellow/red with female bullet coming out. I have know idea what year of truck the tach came out of. How do I hook this up. Is the tach out of a truck with points, that why it has that box on the back? I am trying to take picture but having problems with my photobucket acct. Thanks Mike. P.S. will have major update soon. Motor, trans, brakes, are done. Had engine running, but have to change heater hoses (factory a/c is a bitch to do) and hook up tach. 


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Hopefully you have the tach pictured above. Your year of 620 should have a 6 pin connector taped up in the harness very near where the tach should be. It will have these wires...



Red/Blue.... these two connect to the dash lights


Blue................. this goes to the negative side of the coil

Blue/White....... not used on the tach option. This is constant power for a clock.

Black .............. ground

Black/green...... ignition switched power from fuse box.




If you have this tach...



There will be more wiring involved.

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I have the tach in the top picture, with the wiring of the tach in the bottom picture.  I did find that connector under the dash. In your picture is the blue wire the red under the black wire at the plastic piece, or is this how the tach side is wired. If this is the case I just have to find dash lights plugs to work or hope the case is grounded. I could not pass up the tach for $45.00.  Mike you rock!!!!    Thanks for all of your help. Ramlover14 (Mike)

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