In several forums I see played threads ones that simply end, so I am running out of ideas!
No power at the headlight when low beam is active.
No low beam in the headlight when light switch is set to low beams. Select HIGH on the MFS, high beams work.
Test plug behind switch.
No power to low beams with jumper in place. High beams on when jumper is in place.
New MFS.

Help?

 

Your post is kinda all over the place.
1st assuming you have POWER to the headlight switch? yes
Assuming you used a jumper from power to the LOW BEAM CIRCUIT at the headlight switch connection and still no low beam but got high beams instead? (do note that if high beams are on the low beams will go off)
Also assuming you have a multi-meter for testing.
Have you ran a continuity test from the power to the low beam tabs on the headlight switch?

 

I DO NOT KNOW WHY. IF SOMEONE CAN EXPLAIN THIS, I WILL BE EXTREMELY GRATEFUL.
Low beams don't work on the truck. Highbeams, yes. Low beams, no.
What it can be: headlight switch, MFS, fuses, relay, wiring, or any combination thereof. Side note: I despise wiring issues.
After a week of troubleshooting, I decided that it is NOT a power issue or a switch issue. It is a WIRING issue. Did i mention I despise tracing wiring? In a loom? Or sheathing? I situate myself behind the right headlight, and flash my light down there.
30 seconds in: Why are there two wires with ring terminals not connected to anything? I know that they have nothing to do with the battery because 1) that wouldn't make any sense, and 2) they don't reach the battery. So, I grabbed some wires and jerryrogged these wires...and my right headlight came on. I tested the switches and everything is good! The low beam comes on with the switch in the ON position and turns off when it is in OFF or PARK. Turn on the high beams and they work. The low beam stays on when the high beam is on but they are separate bulbs and I can live with that.
I do not know why the low beams are deliberately disconnected. But now I need to figure out where the wires for the LEFT low-beam bulb are!

Wires were found, it was a VERY professional job. All the excess wire was tucked away, everything was in plastic sheathing. All in all a good job...except for the fact that someone disconnected the low beams. The wife and I discussed it, and came to the conclusion that it was disconnected by one of my FILs friends to keep him from driving at night.

 

I’m glad you figured it out

 

Thanks. It was less fun than I thought it would be!