Hood Tach Wiring with Hyperspark
 

I am getting around to trouble shooting my reproduction 3 wire hood tac and have run into an interesting issue.

It is wired to the wiper motor via a spade connector and works, but only when the wipers are on!! So, I am thinking bad ground, but the ground to the firewall tests fine. The always on light in the tach comes on with key on power. Ive tested the power source at the wiper motor for key on power and it is fine.

I am running a Sniper 2 with Hyperspark and PDM. I am taking the signal from the gray tach out wire and it is accurate, but, again, only with the wipers on.

What does the Pontiac brain trust think my next step should be. I am hoping it's something simple and being a novice I am just over looking it.

Thanks!!

Connecting to a wire at the wiper motor itself?
What color is the wire?


:confused:

Originally it was on the black with yellow stripe wire. I did some poking around to see what had good power with the key on and switched it to the middle position of the 3 wire connector by using a spade connector.

Either way, I get light to the bulb in the tach, but I only get actual tachometer function with the wipers on. I think this would rule out needing a tach adaptor, as it would never work. It feels like a ground issue, but i verified good ground.

SO FRUSTRATING!

I think you need a blue with black stripe wire?
The yellow is after the power is applied?


:confused:

I don't have a blue with black, unfortunately. I know its getting 12v power because the light comes on. I finally just spliced in a spade connector and stuck it into the middle of the 3 wire connector to the wiper motor. Same situation: Light in tach comes on with key, but no tach unless wipers are turned on.

At one point, I convinced myself i needed a tach adaptor, but now that I have an accurate tach with wipers on....

The wiper motor is convenient, but maybe I need to try a different 12v source?

I guess I should have asked 1st how is the tach supposed to be wired?
Does it need 12 volts to make the tach work?

Don't know what Hyperspark is.

Stock just uses a wire to coil and a ground wire.
A 12 volt source is just used for the light. (usually for nighttime)
3 wires total. (unless housing is the ground then just 2)

Also what car and year?

:confused:

do you know if your repro tach requires a 12v supply to operate? As was mentioned, the OEM for those years only required a gnd, coil negative, and +12 for the light.

George

It's 3 wires and was originally wired to the wiper motor, the coil negative, and ground.

Hyperspark is Holley's HEI distributor, coil, etc. It has a wire out that is supposed to work with these old style tachs. Its crazy to me that wired the same way (except not to the coil, but to the tach out), it works but only with wipers on.

Maybe, I do need that tach adaptor.

I believe the repro requires 12v to operate.

I would try a different source?
The wiper motor is a strange breed.
This is wired to the wiper in the engine compartment correct?
(not running a wire from inside)


:confused:

Sorry off topic but, What tach are you using? I have an older hood tach from Ames in 2002 and it won't work if connected to my MSD ready to run distributor. I have to connect it to my coil.

What

Yes, in the engine compartment.

Unknown, it came with the car. It was originally connected to the coil, but from what i read, now that im using the Hyperspark coil, it will kill it.