I would like to know how you are performing the electrical tests.
are you using a volt meter? or is it an electrical gauge from a dashboard?
are you connected directly to the battery, and while the jeep is running, and you turn the lights on, are you inside the cab, and where is the volt meter?
when you turn the headlights on, and the motor starts to drop RPMs, is it like the jeep is running out of gas, and the motor just slowing down, or does it sound like the motor is under strain, and getting 'bogged down' until the motor finally dies, turns off.
And again, are you reading the volt meter while you are turning the headlights on.
not before, or not just after. but during, while the motor rpm is slowing down.
how long does it take from when you turn the headlights ON until the motor starts to slow down, and then after it starts to slow down, how long does it take.
getting some video with sound, with the volt meter in the frame would be awesome.
replacing the wiring for the headlights is kinda easy, and suggested so you can install high power headlamps. that new wiring harness will have heavier gauge wire, and will be independent of the motor wiring.
also, thinking out of the box a little.... is ur fuel pump an electric fuel pump, or mechanical. the older, and carburated motors are not electric. at least not the stock setup... my previous owner disconnected my mechanical pump and installed an inline fuel pump on my motor, and I hate that....