factory tach wiring

[trap4x4]

Hi folks....new to the board.Working on getting a '75 sierra 25 4x4 working after sitting in a field for the last 20+ years. Need a wiring diagram or pictures of the factory tach wiring in the engine bay. A pic of the fuse box would help also. Specific question is...does the brown wire run from underdash thru firewall to a "selinoid" on the firewall in the engine bay,to spliter plug and then to the HEI coil????Thanks again.

[Russell]

If you are infact running an HEI rather than points on the truck, the white wire goes to the Coil terminal on the HEI cap, the black wire goes to the ground (the factory slot is above the kick panel on the driver's side wall, it is just bolted there and should have a couple other wires going to it already) the pink wire plugs into an ignition switched power source

I can get some pictures later if you want

[ElGracho]

My crew cab has what you describe with the wire going to the coil. It is a wire that goes from the tach connection to a little metal box near the brake master cylinder on the firewall. I think it has to do with the kickdown switch on the TH400. I tapped into that wire for my tach just like you are describing.

The other possibility if that isn't what you are talking about is the little round metal can mounted on the firewall directly behind the distributor. That is a condensor (or capacitor if you want) that is there to lower the interference from the tach wire to your radio.