Tach wire and relay

[13matsc]

Hi friends,

Was thinking about wiring up a tach on my 85 GMC C25, but when i looked at the distributor, there was already a cable connected. Where does this lead? The truck has both AC and Cruise control. Both are partially removed for various reasons.

Also, whats the function of the relay originally mounted on the driver side valve cover? Picture is found online, i mounted mine on the firewall when changing valve covers.

See pictures for reference.

Thanks!

 

[nvrenuf]

There is not a wire connected to the distributor cap at the tach slot, it’s a small 1/4x1/4 slot that should have a connector like the ignition wire. The ignition wire is in the slot closest to the firewall and the pick up coil plug is behind the tach slot close to the distributor cap.

 

[13matsc]

Not sure what you mean? In the pictures I posted you can see the cable connected and disconnected from the tach-slot at the distributor cap.

Am I missing something here?

 

[nvrenuf]

I see it now. In the first post I didn’t noticed the loose connector hanging, I was just looking at the cap.
At this point, you’ll have to trace that wire because that slot should be empty on a truck without a factory tach.

 

[Turbo4whl]

Electronic spark control will use the tach port. It usually will have a short piggyback empty plug you can use for the tach signal.

If it does not, you can add the piggyback jumper.

 

[13matsc]

Allright, thanks. The truck does have HEI. So i will need to look under the dash probably, as it will lead all the way there?