Really confused

Ok so short back story, motor blew last April was replaced ran great. 250 miles later my transmission went ( 175k on it and had to drain fluid replacing the motor ). So I did the 5 spd swap. I wired up the vss but car is not on the road. So back in September I did the trans swap and before tearing everything out I had the car running for while. Car ran great. Swap done and at first I had lights on my cluster. Cluster just randomly came on again one day when I started it up. Now the car was idle8ng horribly pulled the distributor cap hit it sand paper and it ran good again. So new cap new rotor. Start it up and again it's running like shit. Today I start it up and it idles perfect....now im like wtf it's normal? Turn on the heater or headlights and it starts to jump. I unplugged the vss figuring it was wired wrong and same thing. So now the car is off...not running.. key in the on position headlights are on im standing at the engine bay checking connections and my headlights are going off and on like I'm playing w the switch.......help....pls.....im lost.

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Also just a rundown of what's been replaced just fyi
New distributor cap
New rotor
New plugs and wires....done at engine replacement 250 miles on them
Plenum gasket
Obx headers
Catback exhaust
Motor mounts
Transmisson swap
Swaped out my dash....car ran great before and after.
Valve cover gaskets
Cold air intake

Everything was done at motor swap time and car ran great for the few weeks after, was running great till recent after trans swap......mind you i moved the car the same day I finished the trans but it ran kinda lumpy that day.

Reinspect anything that was recently removed for the transmission replacement.

That was the first step since I unhooked the wiring to make it easier and not have shit hanging in my way. All the grounds are tight all sensors are plugged in. And the headlights going on and off had the relay clicking pulled it moved them around and I mean all
Of them and same thing happened still. Also just before the headlight shit I started the car it idled fine I turned on everything a/c radio and lights.....then my radio display disappeared but it stayed lit up and my tach dropped to 0 but the car was running.

is your charging system charging? is the alt fuse on the battery blown? The tach runs off of 12 volts and same with the radio, BUT the radio lights are like 5 volts I think. I had my alt fuse blow and I drove the car for like a week before my rpm died and then my radio and then like 2 mins later the care shut off. make sure your charging and seeing 14 + volts at the battery posts

I was thinking the alternator was bad. Car has been fine until this and when I had it running last I unhooked the battery to clean the ground post and it shut off but I haven't checked to see if it was bad. Ty I'll start there and see where that goes.

2 things I ran into while messing with my V6. The battery cable ends are crap. Replace them and the ground cable where it grounds to the body after leaving the battery terminal. Double check to make sure that the alternator connector is fully plugged in. It will do strange things if it is not snapped in completely.