I have a 1990 tpi 350 my alternator is not charging with the key on I have power to the alt thru the plug in the red wire the brown wire has no power. I have power thru the battery cable rom the back of the alt the alt is testing good and I'm pulling my hair out trying to find out why it isn't chargeing it was chargeing last week my fuse is good and I have the fans hooked up to a toggle switch the replays are still plugged in any ideas of what is wrong or if anyone knows if the brown wire suppose to have power

 

After I crank the car I have 14 volts checked with voltmeter when I cut the ac on the alt will charge for a min or two then the brown wire loses voltage and alt quits chargeing what's causing this

 

No power to the brown wire, no charge. It really is that simple. The brown wire is tied into the C/H FAN fuse at the primary fan relay. For some reason, this wire seems to get REALLY hot at the relay terminal and melts the insulation, which can cause a short or broken wire if shifted enough, and the heat creates resistance, which makes the problem worse and lowers the voltage passing through the wire. Fix the brown wire or connect the alt end to another ignition feed...

 

I did connect it to a secondary ignition 12 v with key on and when the fans are on and ac I have 14 chargeing and 11-12 on gauge ac and fans shouldn't be drawing that much current this just started happening

 

Personally, I'd like to see the charging voltage a little higher than that, but it should work okay. Gauge is probably off... Most are.

The wiring harnesses in our cars are a MINIMUM of 20 years old now. The problem with the brown wire in the FAN circuit has been developing for a good long time. I don't know why that particular set of circuits (same also happens with the fuel pump relay) seems to draw so much current (and on the relay coil side besides) or whatever happens to destroy the insulation on the end of a good number of the wires, but it does. I haven't personally seen one car with the older style relays on it that doesn't have at least one relay in that corner with bad wiring (seen mostly sixes, which have the 2 relays together).