NEED SOME HELP WIRING MY HOOD TACH. I wired it up and it only works with my interior or headlights on. How do I wire the grey wire with the two connectors?

Thanks
John

There should be three wires. Black to ground, usually to a small bolt/screw on the firewall. The grey one goes to power (this is supposed to go to a power source that is "HOT" when the key is in the "run" position. The best place to get this "switched power" is right at the wiper motor, which is right there by the tach. I crimp a spade(male) type end on the grey wire and push it right in next to the power wire on the wiper motor plug. Then, the last wire (usually purple) goes to the (-) negative post on the coil. That's it, should take just a couple of minutes to wire up a tach.

Thanks... So, the tach lights are on all the time the tach is running?? Is this how the stock ones were?

The tac lights on when motor is running to help keep tac dry.{condisation can fog lens}

Oh that makes sense. Where did the stock tach wire harness connect to for the power source?

If I remember correctly a stock hood tach harness draws it's power from the bulkhead connection on the firewall...

The manual shows to the fuse block but I put mine to the wiper switched power wire.

i think the fuse panel marked lamps only has power when light switch is on.... did the stock tach have the 3 wire set up?

Yes. I've seen original cars and the hood tach lights up as soon as the key is turned "on"...

Hey guys, I realize this is really old but helpful, just wondering if car has a MSD Box, the Black Purple wire with inline fuse would go to the box instead of the coil, correct?

68 Tach Harness