Sounds like something may be wrong...
I have a "all on" headlight also, only it's not the cheap stuff some are selling now. Mine is a complete wiring harness with 2 relays that are connected to the battery not the light switch like OEM or some other harnesses.
I can and have run all lights...
Did you use a scanner to time it after installing the IP? You can't just install and go, it doesn't work that way ..
Edit... I see you didn't replace the IP, might still be a good idea to plug in and see what is really going on.
Personally, I think you might need to except you have a 30+ year old motor, weak rings, slick cylinder walls, IP wore, among other things, until you go through the inside of the motor not much is going to change... Such is life...