My truck has no high beam, the indicator light comes on in the dash but no juice to the lights. (84 chevy military ambulance)
Did you use a volt meter to determine no juice??
Check the bulb or fuse.
I don’t know your truck, but my guess would be a relay, or maybe both lights happen to be out. It is not that unusual.
Test light, I can check with a volt meter
I have found the relays and will get new ones anyway. I didn’t mention it has a minute mount plow. The lights work fine on the plow.
Did the ambulance have emergency lights? Many emergency vehicles have a “Wig-wag” flasher installed to alternate the high-beams. You may want to look under the dash to see if it was removed.
Also, the plow lights could be causing problems. On some plows, the factory lights stop working when you plug in the plow lights. Check the wiring for that.