electrical ground

Richard,
The easiest way is to look for a daisy chain of black wires. An example would be all the grounds for the lighted instruments. Follow them back to the start where it comes out of the wiring harness from the engine. What are you doing? I ask because both the ground and positive wiring from the engine are notoriously undersized and suffer from a voltage drop with any load. Many add or up size both and if you plan on adding any load, I would suggest it. There are several threads on it. The FAQ thread in the maintenance section will have links to the threads.