I have a 1990 vert and the headlights won't stay on high beams. I have ruled out everything but the CPU. Is it normally the latch FETs in the CPU that causes this? I'm very handy with a soldering iron.

 

How long do the high beams work before the low beams take over? If you pull back on the lever do the high beams stay on as long as you are pulling back the lever?

 

your HI beam relay at the front of the car is shot. (Foxed.ca will give you manuals on your car..free)
If you put 12v to it,that will engage the HI's and allow them to stay on(saying when you hit the switch to HI that relay kicks on).Relay contacts and the lights stay on.
If it is giving you HI when you pull the switch back But not when you let go then the relay is done.

 

Thanks for the info misterstyx, that's exactly the behavior I have been seeing.