I have a 1981 Pickup, 22R, Manual, 4x4. I got it with an electric fuel pump, electric radiator fans and an aftermarket head unit stuffed in the dash.
I installed aftermarket hvac into the truck as the stock components were missing when I got it (no heater core, blower, etc.) Seemed to work ok.
I decided to add some KC lights, a set of 4, to the roll bar. Everything is fine with them off but, when you turn them on, the stock alternator couldnt keep up.

I switched to a 3 wire setup but, I'm noticing that when everything is on, voltage drops to below 12 and does not recover.
At idle, it puts out 14.4v. If I turn on the A/C or increase the load with lights, it but will recover slightly. If at any point it drops below 12v, the alternator output never comes back up.
Like the exciter shuts off. I have the sensing wire/exciter run to a bussbar connected to the battery. Added a 2ga. power wire rung along side the original white wire to accomodate the additional amperage.
Increasing RPM seems to have no effect.

My assumption is either:
A) Bad Ground/Inadequate Ground
B) Bad Alternator out of the box

Not sure what else to check as I am brave enough(or dum,b enough) to tear apart anything and try to figure it out but, my familiarity with this truck is limited to say the least.

Thanks for any input!

 

Maybe you got a low amp alt that will not keep up. I'd have the unit bench tested

 

Turns out the alt was only putting out about 60 amp. I bought a CS144 and adpater to wire it in. 240a shoulds do the trick lol