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Thread: Rear combinatin bulb not giving light

  1. #1
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    Default Rear combinatin bulb not giving light

    The rear combo bulb that does rear and brake lights doesn't give any light appart from when braking. There is another bulb there that seems like rear + sign light, this I assume is what have been giving me rear light before.

    Is both supposed to work as rear lights? Or just the one on the bottom for the sign?

    It might be my bulb that is bad. I can't check right now because it is snowing heavily.

    So to explain further, its the small thread in the combo bulb that I expect to give light constantly that doesn't give any light at all. The big thread for the brake light works as expected.
    GS1000G 1981

  2. #2
    Redman's Avatar
    Redman is offline Forum LongTimer Past Site Supporter
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    THe bulb with two filaments (threads) is the tail light and brake light. I cant tell you if the bigger or the thinner is the tail or the brake.
    But good that you can see them. If you tap on the bulb, maybe can see the filament vibrate, maybe than can see if one has a gap burnt out or if is broke somewhere. If can see on side vibrate more than the other side, that gives you a clue.
    But is always hard to check electrical problems with your eyeballs.

    Can check continuity (Ohms) of the bulb filaments with a meter, from one contact on the bulb to the base of the bulb. Each SHould be some ohms, i dont know specifically how many ohms, but some. If burnt/broken open will be infinite ohms (flashing 1 on some meters).

    Can also check for voltage on the bulb socket. Brake light is the White wire. Tail light is the Brown wire. and, of course, blk/wht is ground. IF dont have power on the brown wire, also try turning the key to the Park position. Report here.

    .
    Last edited by Redman; 05-08-2021 at 11:52 AM. Reason: spullungh

    Had 850G for 14 years. Now have GK since 2005.
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    Gorminrider is offline Forum Sage Past Site Supporter
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    KEY OFF! then Clean the contacts inside the socket. No go? Replace the bulb. No Go? Report back.

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    Quote Originally Posted by Gorminrider View Post
    KEY OFF! then Clean the contacts inside the socket. No go? Replace the bulb. No Go? Report back.
    Cleaned contacts, no dice. Checked with volt metre. Rear has no volts. Brake has 6.5 (battery was 12.6 volts). Checked brake using a lock chain on the rear brake, not sure if its progressive.

    Bulb is good, after messuring I tried placing it in the wrong hole, and both filaments lit up.

    I still lack the 5 watt bulb, I think that will give some rear light and maybe enough. I am assuming that bulb is what made me miss the other not working.

    Hoping I can find a bulb tomorrow so I can go to my friend and have my exhaust welded. Im afraid to try the bolts myself in case they snap.
    GS1000G 1981

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    Gorminrider is offline Forum Sage Past Site Supporter
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    Then you are into the wiring. Seeing as both brake and tailight are funky, First check the ground near the tail lamp. It's the Black/white stripe. Disconnect the tail-lamp's and touch to the fender...if it lights, your ground swire or the bulletsocket is the fault. The same B/W grounds the brakelight. Again, touch to fender and test the brakelight using front and rear..... The multiple x4 bullet"plugin" near the tail lamp is Often funky per loose fit -give it a little squeeze before pushing the bullet in....

    By now you should have clues as to what's not getting power and why...if the ground is ok, you are down to two wires.

    Next, the brown is the tailight's "+" power. It gets its power from the KEY switch, which taps from grey which taps from Lights fuse blahblah but if your gauge lights and headlamp are ok, wiring trouble can only be between the key switch and the single.... push-together connection near the rear-a single brown wire all the way

    The brakelight is the white wire. has its own fuse. Wiggle,clean, then suspect the brake light switches. There are two.Either one will light the brake. First the foot lever. Often funky. Move the rod in and out a lot to see if that helps Then ADJUST it......Next the handlebar brake switch. Again, often funky...adjustable, but barely. Tutorials abound but I just replace mine with an Ebay hydraulic type to save "fixing it" every year.
    Last edited by Gorminrider; 05-15-2021 at 11:56 AM.

  6. #6
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    If I were to venture a guess, these wires is responsible for my issues.

    The beige wire gives me 0.2 volts normally and 11-12 volts when the brake is pushed.

    I guess I have to rewire the entire light? Can I buy original wires to replace them?
    GS1000G 1981

  7. #7
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    Somebody's used a bedamned ScotchLok on those wires.
    If you can be bothered, you can cut out the bad section of each, replace them with fresh wire soldered in to keep the original length and make sure to put a suitable length of heatshrink tubing over the wires before soldering up.
    ---- Dave
    79 GS850N - Might be a trike soon.
    80 GS850T Single HIF38 S.U. SH775, Tow bar, Pantera II. Gnarly workhorse & daily driver.
    79 XS650SE - Pragmatic Ratter - goes better than a manky old twin should.
    92 XJ900F - Fairly Stock, for now.

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