Hood Tach Won't work

Trying to nail down the last few things. The hood tac on the GSX doesn't work. Tach is fine - it checks out and works when power is taken from the coil. Wiring going into the firewall is good. What else could be the problem ? Where does the tach pick up the power from the coil ? All new engine wiring also that matches the original wiring. thanks

 

If it is a reproduction hood tach, it will need 12 volts to work, unlike the factory hood tachs. They are wired different than the originals.

The negative side of the coil is what sends the RPM signal to the tach. It is a brown wire on a factory tach car/harness. The coil should have a pink wire going to the + side. The - side should have a black wire going to the distributor and a brown wire going to the dash harness. Then there should be a hood tach harness coming off the dash harness to the hood tach.

It’s been 12 years since I installed a reproduction hood tach, but I think I wired it by sending 12 volts to the tach when the ignition was turned on, which also was used for the lights in the tach. Yes, the hood tach lights were on whenever the key was on, but it’s what was necessary to get the tach to work with the factory three wire harness.

 

thanks - it is the original tach. Friend checked it and the tach is fins. Problem is in the wiring somewehere. Everything under the dash is original wiring. I did take everything out of the car when I restored it.

 

Cheers Brad The tach feed wire is taped to the outside of the engine harness. It runs up to the firewall and connects above and to the right of main harness connector .There is a round rubber boot I'm pretty sure it's a brown wire. I don't think the repro harness comes with it ,but you can get separately hope this helps. Tim

 

First thing I would try is jumpering the tach signal directly from the coil to the tach. How did your friend verify functionality?

 

Check the fuse as well.

 

Will Do. We took the original tach and jump wired it to the coil.

 

Thanks Tim - I matched the repro harness against the original and they were the same, right down to the TCS wiring

 

I had big problems with my rebuilt tach. They wire it different. I forget exactly how I did it but I got power somewhere else and wrapped wire into harness so it looked stock. It was a royal pain. I worked on it for days.