headlite question

The outboard bulbs should be three prongs and are the hi/los
The inboard bulbs should be two prongs and hi beams only.
Therefore if the inboards do not lite but the sockets shows both power and ground then you need to pull some amps through the power wire and see if it will co-operate. The headlights require more power than what a test light or a VOM can pull. Having12 volts on both legs of the two prong bulb simply indicates that the filament is good.
You can pull the amps by powering up the bulb on either leg, and grounding the other to the battery. If the bulb now lights, you have a faulty ground. If the bulb still does not light,pull it out of the socket and power it up from the fully-charged battery; if it still does not light, throw the bulb away. But if it now lights. then you have a faulty power supply.
After you fix the supply side, and the bulb still does not light. then you still have a bad ground.
The headlight socket grounds should be tied together in the harness and a short jumper from there to the core support usually on the driver's side. Then there must be a ground return from the core support to the battery. You may be able to take a shortcut by simply jumpering the core support to the battery. If the lights now work, then just fix the ground.
Sometimes there is a ground jumper from the firewall to the passenger side head. This reroutes the ground thru the engine and out the ginormous ground cable back to the battery.This jumper is often forgotten during an engine transplant or RnR.
This is how I remember it..... good luck