GM produced millions of cars and trucks that had HEI ignitions and no tach.Nothing was plugged into the tach slot,nor needed to be.If you do decide to install one at a later date,the provisions are there.
So, remove the dark green wire coming from the ballast resistor to starter solenoid; remove green wire from coil to solenoid; what about the tan wire that goes to the ballast resistor? Where would I attach that?
You need 12v to the HEI when the key is in both the crank and run position. I could be wrong but I do not believe any of the terminals on the fuse box have 12v WHILE cranking. You will need to run a wire from the HEI directly to the BAT terminal on the ignition switch. be sure to use a grommet where your wire passes through the firewall.