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Taillight dark, blows fuse #2 when key turned on


Effjay

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Hoping for diagnostic help from dirtrider or others here with ideas. Searched prior similar topics without success.

 

Rode the R1150RT Saturday and guy behind said taillight was out but normal turn signals and brake light function. Seemed ok otherwise, so continued 270 total miles. Moto equipped with aftermarket Hornig LED lamp housing assy (external wirewound ballast resistors plus associated wiring), so figured something came loose for an easy fix when I got home.

 

Yesterday, pulled the Hornig assy and checked all connections. Nothing loose, so checked fuses. Yep, #2 4A blown which controls taillight etc. Replaced fuse and "pop!" as ignition turned on. Disconnected OEM rear harness wires which control brake light and taillight functions and tested taillight wiring (gray/white & brown wires) using OEM incandescent socket/bulb as test lamp plus another #2 fuse. Blew that one too. Verified OEM socket/bulb ok by temporarily connecting brake light wires (gray/yellow & brown). Likewise confirmed Hornig brake/tailight sections function ok by temporarily powering off same (gray/yellow & brown) wires. By elimination, concluded no problem with Hornig aftermarket lamp assy nor associated Hornig wiring nor OEM socket/bulb. No other fuses blown. All relays seem to function ok. No short-to-ground on that gray/white wire evident nor would seem likely? Unplugged accessory power cables under seat direct-wired to battery (Zumo gps plus Bags-Connection electrified tankbag, fused inline, functions normally), retested and blew more fuses. Need more 4A fuses now, so I'll wait for help on what to check next.

 

Unsure if ABS was working Saturday 'cus dash light extinguished normally as ridden away with self-test completed. Servos whiz normally. Unsure how long this condition has existed since I usually ride alone, not at night and hadn't noticed lack of taillight function. I replaced battery with new BMW gel type last summer - kept on BMW brand tender. Haven't removed tupperware, hoping to identify possible location of short without disassembling. At this point, moto is fully rideable and safe in daylight. OBTW, total of just 12.4k miles since new.

 

TIA...

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Afternoon Effjay

 

 

You have a few things that it could be.

 

The side light is on the #2 fuse circuit so take a look there for a shorted wire or the bulb filament fused & shorted inside the bulb itself. (quick check is to install a new side light bulb or just remove yours)

 

Or you have an issue inside the ABS controller shorting the rear light circuit (maybe unplug the ABS large plug & see if it still blows the fuse).

 

Or you have something else (non BMW) wired into that #2 fuse.

 

Or you have a wire shorted to ground on the power supply side of either the rear light or side light circuit.

 

If none of the above easy places to check then we will have to separate the circuit onto small (testable) circuits & track it down area by area.

 

Added, if you can't easily find the problem you can install a series of 2 automotive 4 way flasher units (in series with wire pigtails )--- (needs to be the multiple bulb type) in place of the #2 fuse.

 

That should keep the circuit flashing while you wiggle & move things but still protect the circuit from burning up.

 

When the lights start flashing or the flasher unit flashing rate changes you have probably effected the shorted area.

 

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Afternoon Effjay

 

 

You have a few things that it could be.

 

The side light is on the #2 fuse circuit so take a look there for a shorted wire or the bulb filament fused & shorted inside the bulb itself. (quick check is to install a new side light bulb or just remove yours)

 

Or you have an issue inside the ABS controller shorting the rear light circuit (maybe unplug the ABS large plug & see if it still blows the fuse).

 

Or you have something else (non BMW) wired into that #2 fuse.

 

Or you have a wire shorted to ground on the power supply side of either the rear light or side light circuit.

If none of the above easy places to check then we will have to separate the circuit onto small (testable) circuits & track it down area by area.

 

Added, if you can't easily find the problem you can install a series of 2 automotive 4 way flasher units (in series with wire pigtails )--- (needs to be the multiple bulb type) in place of the #2 fuse.

 

That should keep the circuit flashing while you wiggle & move things but still protect the circuit from burning up.

 

When the lights start flashing or the flasher unit flashing rate changes you have probably effected the shorted area.

Per your usual, DR proves to indeed be "The Oracle" of BMW maladies...

 

Frankly, I was concentrating solely on the moto's aft end having had the comment of "no taillight" while riding. Clearly now, there was no front running light function either. So with more spare fuses, removed both fairing mirrors plus bulbs from sockets (amber incandescent under smoked lenses matching Hornig LED smoked rear housing). Installed new fuse and rear taillight illuminated with no popped fuse! Installed LF (as seated) bulb and it lighted. Did same with RF bulb with same result during which root cause found. At some point in prior ownership, fairing removal trapped and pinched power lead wire exposing copper conductor and shorting to ground. Its still pinched but it'll be an easy fix now!

 

Many thanks!

 

410880619.jpg

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