electrical

I am a proud first time owner of a used 1990 Heritage softtail
I am having problems with the highbeam/driving lights
cutting out sitting or driving? where do I start? I dont think it
is in the High beam switch. Low beams work just fine.

Please be more specific. You say high beam / driving lights?

Since it is against DOT to have driving or spot lights operating while the high beam is on the bike originally came wired so that when the high beam is on the spots are off. There are some people that alter the wiring to makes the spots operate either way. Then, they add 50 watt halogen spots and a 60/100 headlight bulb. This does a few things to the bike. It definitely makes you more visible to oncoming traffic and totally blinds them at close range. It adds a lot of heat to the headlight housing so that when sitting still at a light a little rain can cause the headlight to shatter so dim them at lights or in slow traffic if your setup is this way. Third and most importantly it adds several amps of draw on an already barely adequate charging system so frying your stator while driving in slow traffic is pretty common.

This combination also puts a lot of load on the 15 amp breaker so that is why I need more specifics. Does it cut out anything else or just the lights? Switching the high / low immediately gives you low beams or is there a brief delay?