Pulsating lights

Alternator is new. I will try the dark test tomorrow. If I unplug the regulator the problem goes away. Another thing happened I might mention. When I rrun the car for along time the left turn signal doesn't work,but the right side works fine, however when I put the signal on left, both tail and front turn signal stays on bright without the flashing. Let the car cool down and the left signal works again.

The 2 could be related.
You could pull the signal fuse, check condition, then pull the flasher and check condition.
Question.. do the oem gauges work ? If the original gauge voltage limiter is there, Unplug it. There should be a paper insulater between that limiters' noise supression capasitor lead and the printed circuit board. I remeber seeing a short there. I dont recall the symptom details. I've seen the oil pres' sender shorted to the distributer housing too.
We'll find it