1990 F-150 4X4 302 Starts great runs fine for a short while then the Battery Gauge starts to waiver drastically, if lights, turn signals or A/C (especially A/C) are operated sometimes kills the engine sometimes not!
I had the bat. tested (bad) and changed it still had the same problem, then the Alt/reg. tested (good) changed them anyway, still getting same results.
Also when driving down the road and come up to a stop light or a turn that I have to slow down (quite a bit)to carry out progress the engine dies!!!!
Any and all help, info, and sugestions will be greatly appreciated!!!!
Thanks Allen

 

Perhaps you have a loose connection somewhere in your electrical system. Start at the battery.

 

A friend had the same thing, check all the wires, esp to the fuse box