Oh no, help me out here 1955 chevy truck.

[yellow400ex05]

Alright so I had a pulsating/surging light issue on my truck, so I was told it was a bad rectifier in the alternator so I put a new alternator in it and a good battery. So tonight I was driving and everything was fine but after an hour or so I noticed my headlights/dash lights getting dimmer and dimmer the longer I drove until they were so dim you couldn't drive it. So I stopped once and the lights went to normal brightness for a second til I hit the gas again and they went really dim. When I parked it and waited for a tow truck I noticed that when I turned on the lights it runs badly like a misfire and wants to die, when the lights are off it runs fine. What the heck causes this!?!?!? Alternator is working okay but of course my battery is dead now.

[Speedbumpauto]

I'd be looking for a bad ground. If batt - goes to engine, the way I like it, then make sure there is a good ground from the engine to the frame. IMO, you can never have too many good grounds. It's easy to get the ground cables with 2 wires, a big and a smaller one so the battery can be connected to the engine and frame by the same cable.

[starterman99]

Sounds like a slipping belt.If the alternator was charging the way it should your battery would not be dead.The more load you put on the electrical system the more the alternator has resistance to turning causing the belt to slip.Once the voltage in the battery is depleted it will start to run bad and then quit.

[_Ogre]

in your original thread you posted pics of your ground cables and were told to redo your ground cables
that was the cheapest and first thing you should have done
your battery and alternator may not have been the issue

[OrrieG]

Been there, you were just running off the battery with no charging circuit. I have had loose belts and broken alternator mount do the same.

[Nev68]

Originally Posted by starterman99

Sounds like a slipping belt.If the alternator was charging the way it should your battery would not be dead.The more load you put on the electrical system the more the alternator has resistance to turning causing the belt to slip.Once the voltage in the battery is depleted it will start to run bad and then quit.

I had the same on my 68 Camaro recently. Belt slipping due to a small leak at the front seal, a small amount of oil was getting on the belt and the belt slip on the pulley.