I was driving the other day... Went to turn on the headlights and the truck shut off... It's acting like it isn't getting any power but the battery test fine... I checked the fuses and nothing was bad there.... What's the next starting point?

 

Have you had your Alternator tested to see if it is putting out?

 

Disconnect the head lamps at thier plugs to verify it's not a short in the wiring. Granted the fuses should pop when this happens but they don't always. This is a simple check that requires no tools.

You need to check the battery voltage under load, eg headlamps and accessories turned on. Once the voltage drops below 9v the computer shuts down.

The alternator inspections are also in the manual. Link

Autozone or another parts store can do the load tests for the battery and alternator but you'll have to remove them to plop them on the counter for them.

 

Double posted, threads need merged if a MOD spots this
https://www.yotatech.com/forums/f116/91-toyota-267966/