I'm working on an 89 ford f150 and recently put in a carbureted engine with a Chevrolet style hei distributor. I'm trying to get the factory tach to work with the distributor to no avail. I have connected the dark green w/ yellow stripe wire to the tach terminal on the new distributor and have read that there needs to be a frame ground connected to the harness but I have no idea to what wire I need to connect the ground. Can you help? The wiring diagram in the manual leaves much to be desired.