Headlamps turning off when Hi-Beam engaged
 

Interesting one.

I recently replaced my old Hi-Beam headlamps after one of my old ones died with 5-3/4'' Xenon Conversion Headlamp Bulb (High Beam).
Put them in, switched on and aligned them and all was good.
When I finally got around to driving and needing them I engaged the Hi-Beam footswitch and all of the headlamps went out! Not great considering I was driving at the time.
After I disengaged the Hi-Beam switch my main headlamps came back on.
The only difference I can see is the replacements have three pins rather than two but they worked fine when I first put them in, hence why I was able to align them.

Thoughts?

Bad switch. They get full of dirt and the contacts are blocked as well as being under a heavy electrical load when they work resulting in pitting and burning.

Big Dave

I'm not disagreeing with Dave here, not at all. Those old switches get troublesome with age....but,

Excuse my ignorance or presumption here but wouldn't/shouldn't a Xenon bulb use a breaker near the headlight with its' own 12v source so that the extra wattage doesn't flow through the 50 yr old wiring?

Good point Dave. 40 years ago I experienced the same problem with a car I had and it ended up being the high beam/low beam switch on the floor. If the new head light switch doesn't fix it try the switch in the floor.

UPDATE:

Just thought I'd post that I cleaned the footswitch and connector with Electrical Cleaner and an old toothbrush, let it dry and it's working fine.
Hopefully I don't have trouble with the Xeon bulb drawing too much power as B.A mentioned but for now all good.

Thanks for your help!