I just redid the wiring harness on my '84 240 B21A last summer. Not a big deal at all. Carefully trace each wire for continuity from the end back to the grey canon plug at the fire wall to make sure you have the right wire. Then draw up a color coded wiring diagram. Reroute the wires for the, alternator, and oil press. sender from under the crank pulley to around the right side fender well, then down to the engine. You can probably leave the big red wire that goes from the alternator to the starter, it's generally ok. Use good quality #14 or #12 wire in various colors. (Got mine at a marine supply store, it seems to have a higher temp. rating) Cut out the canon plug and use spade connectors,solder, and shrink wrap each connection. Put a dab of dielectric grease on each joint. The whole job cost me about $30. Go for it!