Strange Electrical Problem

[kidsStang 11]

something weird has been going on with my car, if the engine is started and running and I then turn on the headlights the engine dies, if i rev it up and turn on the lights they come on but no taillights or instrument lights but the engine keeps running. thought it might have been the headlight switch but replaced it and no change.just upgraded to electronic ignition but drove it a couple times after converting it and had no issues. so i'm baffled. 

[1969_Mach1 333]

My first thought is check your charging system.  Also, make certain you have bypassed or eliminated  the factory resistor wire that use to supply power to the stock ignition coil.  I believe the stock ignition coil and points operated on a little over 6V which is why the resistor wire was used.  Aftermarket electronic ignition systems need 12V to operate.  On non factory tach cars the resistor starts at the ignition switch and ends at the gauge and stock ignition coil harness connector near the back of the drivers side valve cover.  On factory tach cars the resistor wire starts at the tachometer and ends at the same connector in the engine compartment.

[Footcutter11 23]

I concur with Mach1.  Check voltage at coil to verify 12V.  Any drop will make your electrical system perform pathologically.  Alternator, and voltage regulator can also cause these problems, just verify you are getting ~13-14V with the engine running at the battery.