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Left head lamp went out... no trouble, bulb is easy to get to... but the bulb lights up when tested on the bench with a spare battery and test leads.
Fuse diagram downloaded on line shows F2.7 in the central junction box supplies both headlamps and right side headlamp is working, so it can't be a blown fuse.
Wiggled and jiggled the plug connection to the bulb and the cables.... no joy.
Truck has Fisher MM1 control box installed, so the lighting circuit is modified to run through the plow controls (lights bypassed when plow is plugged in) and I'm guessing something got messed up with that bundle of wires, but if anyone knows of something else I should check I'd greatly appreciate it.
Have you tried putting the right bulb into the left side? I know you bench tested the bulb but maybe you’re doing something on the bench that’s affecting it.
Have you tried putting the right bulb into the left side? I know you bench tested the bulb but maybe you’re doing something on the bench that’s affecting it.
Please explain your thought process on how bench testing a light bulb might lead to a false conclusion.
Please explain your thought process on how bench testing a light bulb might lead to a false conclusion.
— Dave
I'm probably not wording it right... I put 12v + from an old battery on the outer pins and ground on the center pin and both filaments lit up. So my conclusion is that the light bulb is not the problem and since the fuse supplies both L & R sides, and the R side works, the fuse can't be the problem.
So either there's another fuse out there, or somethings went wonky with the wiring... I'm hoping someone else has had a similar problem and will respond with "check the harness connection here/there"
Low beam, high beam, or both on that side? If both, recommend checking the ground wire through the harness.
Fuse diagram downloaded on line shows F2.7 in the central junction box supplies both headlamps and right side headlamp is working, so it can't be a blown fuse.
F07 does supply the entire headlight system but there are 3 more fuses. One supplies both high beams in parallel and the other two protect the left and right low beams all downstream from the switches.
Both high and low beams out on left side. I'll check for continuity through the ground pin (center?) in the bulb plug to ground (frame or neg. battery post?)
Looks like I didn't track down the fuses completely... thanks for the course correction on that one.
After going down the rabbit hole of thinking that it was the plow isolation module... only to find out that wasn't the problem... we discovered it was the bulb plug/socket..
There's zero continuity across the plug from socket pin to wire.
Left head lamp went out... no trouble, bulb is easy to get to... but the bulb lights up when tested on the bench with a spare battery and test leads.
Fuse diagram downloaded on line shows F2.7 in the central junction box supplies both headlamps and right side headlamp is working, so it can't be a blown fuse.
Wiggled and jiggled the plug connection to the bulb and the cables.... no joy.
Truck has Fisher MM1 control box installed, so the lighting circuit is modified to run through the plow controls (lights bypassed when plow is plugged in) and I'm guessing something got messed up with that bundle of wires, but if anyone knows of something else I should check I'd greatly appreciate it.
put a test light on the headlight socket. If fuse is good bulb on working headlight is hood and new bulb is good on bench it’s wiring or connections….might be the switch if it has separate wires going to each bulb….factory . headlight socket connectors are notoriously cheap and burn out. Use dielectric grease on the socket abd bulb prongs when reinstalling the bulb. I dielectric grease all my bulbs
put a test light on the headlight socket. If fuse is good bulb on working headlight is hood and new bulb is good on bench it’s wiring or connections….might be the switch if it has separate wires going to each bulb….factory . headlight socket connectors are notoriously cheap and burn out. Use dielectric grease on the socket abd bulb prongs when reinstalling the bulb. I dielectric grease all my bulbs
