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2009 F250 Super Duty.
Initial problem: No high beam on passenger side. Both low beams OK.
The bulb was good and the black ground wire was good. Bright indicator working on instrument panel, Fuses good.
Found that harness connector showed heat damage. Unable to get replacement quickly so I cut out the connector and hard spliced the wires together. Still no high beam on psgr side.
Determined that fused link in hi beam wire directly behind bulb was open. Hard spliced high beam wire together. Now hi beam works but low beam has stopped working.
Checked voltage on wiring harness:
LOW BEAM
green wire - 1.4 volts
Yellow/brown wire - 0.2 volts
HIGH BEAM
green wire - 8.0 volts
Yellow/brown wire 11.6 volts.
It appears the low beam is trying to come on at the same time as the high beam. Driver's side headlight appears to be working fine on low and on hi.
Any insights into this issue would be greatly appreciated.
Last edited by GRANPA49; Dec 2, 2022 at 06:10 PM.
Reason: additional info
The low beam circuit is driven by FETs individually by side, the high beam circuit is relay-switched and both are in parallel. Each bulb has a ground that is shared between functions. If the electronics in the BCM/SJB detect a fault in the FET circuit, it can trigger a shut down that can only be diagnosed and reset via scan tool.
Wire colors tend to fade and become hard to discern assuming no color vision impairments. Correct colors are shown in the diagram below.
BTW, anyone know what the "HI Series" denotes in the diagram? I haven't seen it before and don't have the time this AM to go down that rabbit trail.
I went back and checked everything again and found that the 10 amp fuse to the psgr side low beam had blown during the repair. I replaced it and now the lights seem to be functioning properly. The question now is why did it fail in the first place. I found heat damage in the connector where the headlight pigtail plugs into the end of the harness (right behind the headlight). I also found an open circuit in what appears to have been a fused link located about 1.5 inches behind the head light bulb. When I got the truck it had the plastic fixtures with halogens. I replaced them with sealed beams. It could be that the halogens were drawing too much current. If that is the case, problem solved. If not, the problem may recur and since I hard spliced the fused link something else will fail the next time. All I can do is wait. Thanks for the replies.
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