AberdeenBikers

OK. Trying and failing to get tail/brake light to work on a GS125.

Here's the mounting.



Here's the new bulb from Shirlaw's which is a 21/5W as per the mounting.



At the mounting there's a healthy voltage on my multimeter with the engine running.



Here's the voltage at the connector under the seat which is a little higher.




So, voltage at the fitting. New bulb (tested with a battery too). Correct type. WHY won't it light up when lights switched on? Everything else works OK - headlights/indicators/dash lights etc- and traced the wire back to the harness and can find no breaks in it.

Ideas??

Bad earth connection? umm....

So there is voltage at the bulb holder, and everywhere else. It's got to be earth or the connections onto the bulb. I think....

If you are getting neither brake nor tail lighting, then it really has to be the earth.
Did you take your readings from the actual parts that the lamp will be in contact with?

Yeah got one probe on the exterior collar that the bulb fits into and the other one onto one of the centre terminals.

Bad earth - ok I'm gonna have to take off the tail light mounting which is a pain coz you have to take off all the rear cowling/bodywork which is held in place by 4 bolts. 2 of which are rusted solid and one is rounded off for good measure.

Thanks chaps. Update tomorrow.

Have you tried switching it off then back on again?

Sherpa wrote:Yeah got one probe on the exterior collar that the bulb fits into and the other one onto one of the centre terminals.

In that case it should light up.

Have you looked to see if the bulb terminals are lined up in the correct orientation to be making contact with the pins. (although it should only fit in one way round)

check the resistanceof the wires and for any bulging which would indicate internal corrosion of the wire. this was a common problem on volvo s/v40s the wires would test ok with the small current of a volt meter but not a test lamp

Big Kneed Al (master of the emergency stop & "stand up" comedian) ( Super Nanny ) wrote: Have you tried switching it off then back on again?

Good plan :I can't believe it's not butter!

chaos wrote:

Sherpa wrote:Yeah got one probe on the exterior collar that the bulb fits into and the other one onto one of the centre terminals.

In that case it should light up.

Have you looked to see if the bulb terminals are lined up in the correct orientation to be making contact with the pins. (although it should only fit in one way round)

As said above, the bulb should only fit one way round.... but often they will fit the wrong way as well......this sounds like what is happening.......it cant be the earth if you took the meter reading off of the side of the holder.

The bulb only fits in one way round - one lug is set higher than the other. The two terminals on the bulb appear to be lined up correctly with the terminals in the mount when the bulb is twisted into place.

Are both bulb connectors live inside the holder at the same time when you only activate one thing, ie, turn on lights, check both terminals, turn off lights and activate the rear brake, again check both terminals.

If both are live then a fault exists somewhere.

Obviously both should be live with the lights on and the brake activated, so, try this also.

Recheck the bulb works, maybe it's been blown since you started trying

What about the old bulb, was it blown? I would try new another bulb before doing anything else. I have a spare one of those if you want it?

Save yourself all the hassle and run new wires, solder them to the back of the old solder joints after you cut off the old wires from the sprung connection backing plate.

Run an earth wire as well, 3 wires in total, much quicker than trying to get rusted and rounded screws/bolts out. Could be all done in 20 min.

Now if only it were so easy on the trailer, licence plate bulbs keep blowing.

IZINBARD wrote:Now if only it were so easy on the trailer, licence plate bulbs keep blowing.

My TT had a bad habit of blowing rear light bulbs. I never did manage to get to the bottom of it so ended up replacing all the rear lights with LED units.

Good idea, I'll have a look into that when I get back.

IZINBARD wrote:Good idea, I'll have a look into that when I get back.

If you need a hand give me a shout.

Has this been fixed yet curious to know what it was

Gismo wrote:Has this been fixed yet curious to know what it was

I'm curious too


No haven't got off my arse recently due to injury so not had another go at it yet. Will keep you informed.

Thanks for the suggestions one and all

Yes. Was a poor earth. Leg is in plaster just now hence the delay in trying to fix it.

Ran a wire from bulb housing to earth and it all lit up. Obviously the probe was getting a good connection but the bulb wasn't.

Then...... put lense back on. Turned on ignition and nothing. No sign of life to any part of the bike at all. Previously everything worked but now it's all dead. Opened up the wires to ignition switch and there is voltage at the connector. There's 12.6V across the battery too. Checked main fuse and it's OK.

Still baffled.