alternator

[duckmanjbr]

If your getting that bad of a draw when the fans kick on you probably have a weak battery. I'm not saying it's bad but just week. I'm running underdrives on mine and even at normal driving RPM I only get about 13 volts max of charge. It's normally about 12.5 volts or so and I know exactly what your talking about when the fans kick on. I've seen the load it pulls, both my fans kick on together, but I've never dropped below 12 volts. Get a stronger battery! Anything less than 12 volts is a brown out condition and could cause damage to other electronics.

[Hit Man X]

There is a reason GM installed 145A alts with the trucks with factory efans.

Install a 145A unit, OVERdrive alt pulley, problem solved.

[txarkitekt]

There is a reason GM installed 145A alts with the trucks with factory efans.

Install a 145A unit, OVERdrive alt pulley, problem solved.

Exactly...

I have the stock 105A unit and with a crank and alt pulley (with both fans on), it pulls 14 volts all the time... If my alt goes out, I will def. switch to the 145A unit.