Headlight on lh side only works on hi beam

I had a international 9400 that did the same thing on both sides. One side it was the plug and the other side the wire corroded through on a tiny spot. I found the very beginning of the wire coming out of the fire wall and used a test light every foot or so and poked holes in the coating on the wire until I found where it quit having power. Then used that liquid electrical tape to cover the holes back up. Don't know if you wanna do that but I was in a hurry. Lol.

 

I would concentrate on the socket area. Either the contacts or where the wire meets the pins is a common breaking area. Like Dickey said it can almost be anywhere on the hot wire.

Make sure you got 12V on pin 87 of the low beam relay. Then check the headlight socket for 12V. (all with low beams on of course. )

Then back up the wire a couple inches and back probe the wire with the needle probe. That should tell you pretty quick.

They do sell replacement light sockets with about 9" of wire you can splice in if you have to. I would use butt connectors and heat shrink. They do make combo heat shrink butt connectors. I buy them at Advance Auto all the time.

 

I ran into almost similiar problem on my truck, turned out to be bad connection between switch and relay. Found out on mine, one side of the switch sends ground to the relay. Thinking the high low switch actually breaks that ground contact.

Not sure it's your situation but might be helpful infor. while probing.

 

I think my case was little different but first cure I changed the headlight relays in the floor door box. That cured mine for a while, then started going out every once in a while like when turning them on or flipping low to high to low. At that point, my switch was giving me problems. New switch has cured it since. I did see the hot wires going to the switch little burnt from over heating.

The guys above have some great ideas also.