I am doing some rewiring in the engine compartment and was wondering what gauge wire i need for some of the stuff. The wire from the msd box to the battery. The wire from the fan to the battery. The purple wire that runs to the starter from the ignition. The wires on the hei.

thanks,

I would use #12 for everything but the fan and starter wire. I would use #10 for these but check the fan mfr. info for what it needs.

Troy.

The battery is not the best location to connect the fans.

The alternator will supply the power for the fans when the engine is running. The alt output is connected directly to the horn relay. From the horn relay to the battery you have a 10 gauge wire with a fusible link at the battery end, J-block to battery. With the fans connected directly to the battery the current for the fans will flow from the horn relay through the 4-5 feet of 10 ga wire and fusible link to the battery then to the fans. This will result in a reduced voltage to the fans and a reduced voltage at the battery for charging.
This (http://www.madelectrical.com/electricaltech/chevymain1.shtml) is good info from MAD Electrical.

If you chose to not rewire as suggested, you should connect the fan/fans to the horn relay, be sure to use a fusible link. If you don't have an upgraded alternator you should, and upgrade the alternator output wire to 8 ga.