Does anyone know the process for checking the headlight plug voltage when switching to high beam? I have lows , but when I switch to high , both go off. The MFS is brand new. Any other help would be appreciated

 

2 or 4 bulb headlight system?

 

2 Bulb system

 

On a 2002 the bulbs have constant power, the MFS connects either one of the filaments to ground. Are these conventional light bulbs or some LEDs ?

 

conventional

 

the rest performed earlier was check all 3 pins for voltage, as you said, they all had constant power, until I switched to low beam, then the middle pin voltage fell below 1V.

 

Sorry it's a little more convoluted. The headlights have separate fused power feeds but the ground connections go through shared wiring via the multi-function and headlight switch. With the lights off you'll see battery voltage on every pin if you back probe and even if you disconnect the plug from one bulb you'll still see the same because the voltage comes through the filaments of the other bulb and the shared wiring. If you remove the connectors on both sides you'll only have battery voltage on the right pin in the connector. The middle pin going to almost zero when the low beams are on works as expected, it gets connected to ground and makes the low beam filament light up. For high beams the left pin in the connector should connect to ground and cause the voltage to go near zero.

 

So most accurate way to verify voltage/correct functionality is to disconnect both bulbs and test the pins for voltage or the lack of ? If all checks out , I guess its entirely possible that both bulbs are likely bad ( low beams only) ?

 

Correct.

 

so to follow up after testing:
unplugged both lamps, no voltage to the middle pins on both sides with lights on, with lights off, brights on or brights off. Zero continuity indicated from middle pin to ground to rule out a short. Any suggestions?