The wiring needed for the alternator and starter is fairly simple.
- large positive wire from battery post to larger starter post.
- starter relay wire running to the ignition switch
- 10 gauge wire with 14 gauge fusible link running to the junction next to the brake booster. This is your constant 12 volt power.
-10 gauge wire with 14 gauge fusible link running to the alternator Bat terminal. This is the alternator charge wire.
Those three smaller gauge wires run up the back of the engine through a metal tube to protect them from the exhaust heat.
Using the starter as a junction is not very convenient when you add accessories or use a high amp alternator, so I would suggest a change in wiring.
- Alternator charge wire can run directly from the battery over to the alternator, using a fuse or fusible link to protect it at the battery end.
- leave the power power wire in place to power the truck fuse block.
- add a 2nd power wire (with fuse or fusible link) from the battery terminal to a junction block on the firewall or fender. This gives you a good power point for adding things to your truck.
One good source for wires with fusible links, and cheap junction blocks, is a Pick and Pull with some GMT400 trucks. Those trucks used larger gauge power wires, and there was often a six terminal power junction mounted up on the firewall. When you pull the junction it will usually already have wires connected that have the fusible link in them.
The way fusible links were marked has changed over the years. You can still buy the old bulk wire, where the link gauge is numerically 4 numbers bigger than the wire it protects (14 gauge link protects a 10 gauge wire). NAPA usually carries a few sizes in bulk.
However, most of the newer ones (in vehicles) have metric markings. For example, a 2.0mm link is equivalent to 14 gauge. The OEM metric links usually have the size (like 2mm) marked on them. It will be a large plastic “barrel” around the wire.
