I have a 79 dodge truck and when you switch from lowbeam to highbeam all lights go out please help thanks

All lights go out?
Or just the headlights go out?

I had a AMC Concord that did that and it turned out it was the light switch in the dash. Easy to replace. Dodges and AMC used the same switches, just the rod where the knob attaches to are slightly different in length. Also check you floor mounted high beam switch to make sure it is functioning.

With the info you provided, it may be the High beam wire is shorted to ground. Can you tell more? the fuse blows?
If you plug in a fuse when on high beam it blows? Stuff like that.
The power from the beam select switch when switched to high, also goes to your high beam indicator.