when good tachs go bad

[ruddyboys]

The needle on my old tach would move. So I just bought a new one (Thanks Chris). I have a 74 but like the look of the earlier gages. Wanted to check out the old and found the PO had the wires removed. Put the wires back on as to the wiring digram, tried to start the car and just heard a click in the engine bay and now power. Took the cable off the battery and tried a gain and the same thing. Took the wire from the coil off and the engine cranked but wouldn't turn over. Took of the power wire and the car started right up. I need to know if this is the tach or some other electrical problem.

[Dave at Pelican Parts]

I don't think I understand what you did.

Which wires did you connect, and which did you disconnect?? Colors and "where it goes" would be very helpful in describing that...

--DD

[ruddyboys]

Ok I hope this pic comes out

With all these wires attached is when the whole car shorted when tried to start (click then no power) removed the neg wire from battery and tried again, sme click and no power. Removed the black and purple wire (to the - terminal on coil) and car cranked and would not start. Removed red and white wire (power) and car started right up. I need to know if this was just a bad tach or some other looming electrical problem.

[Dave at Pelican Parts]

Removed the ground strap from the battery? Or unplugged the brown wires from the tach?

Verify that the brown wires are ground. (Zero or close to zero resistance to battery ground post.) Verify that the red/white wires have +12V when the ignition is on. Verify that the black/purple wire connects to the one on the coil (-) terminal (again, zero ohms or close to it when checking resistance between the two).

Plug the black/purple and bronw wires back in again, tape the red/white up so it won't short to ground. Does the car still start?

If everything checks and the car doesn't start except when that red/white wire is unplugged, I would strongly suspect a short inside the tach. Try to borrow a tach from someone else to see if the car runs with it swapped in.

--DD