1970 Plymouth B-body Tic-Toc-Tac Wiring Harness
by Roger Wilson

       Many owners of 1970 B-bodies want to install the clock/tach unit in their car which may not have been ordered with this option.  Many times at car shows one can tell the unit was installed later because of the way it was wired in the engine bay.  It is not wired to a correct lead coming out of the firewall grommet but usually from a hole made in one of the rubber seals in the firewall using incorrectly colored wire.  Now one can can install the clock/tach correctly with the use of a reproduction wiring harness made by Bill & Rose Evans (8835 Parson Roads; Erie, PA 16509. Phone 814-864-2622). I have seen the reproduction harness and they look very close to the original harness.  Here's how to install the correct harness.

       The dash block off plate that is installed in the dash where the opening for the clock/tach should be, can be removed by unscrewing 3 phillips head screws.  One needs to carefully pull a light socket out of this block-off plate.  This socket then is pushed into the back of the tach when it is installed.  A very small screw driver is needed to remove the small adjusting knob at the end of the small rod used to set the clock.  This, of course, needs to be done before installing the clock/tach into the dash opening, then once the clock/tach is in, it can be screwed back on.  To install the reproduction harness one starts by drilling a 7/8" hole in the firewall at the appropriate dimple. (See photos) 

    From the inside of the car the lead (gray) wire is pushed out through the firewall hole until the grommet is in place.  This lead is connected to the coil.  If one is ordering a new engine wire harness be sure to say you want one with the tach lead.  Then its just a matter of pushing the two connectors together in the engine bay.  If you don't replace the engine harness because it's in good shape, one will need to install a wire from the coil to the female connector coming out of the firewall.  There will be two connectors still under the dash area which are pushed into plate on the back of the tach.  The long wire with the spade is pushed onto one of the places on the backside of the fuse panel located in the glove box.  The clock/tach unit should now be ready to be operational, and it will be very difficult to tell that the car originally did not come with this option.