Help, brake light isn't working, wiring issues?

[gotjeepzj]

I finally got around to installing a new speedo, and speedo sensor on my 1979 gs1000L. I was going to conquer my brake light issues also. My brake light doesn't work. It used to work sporadiclly when the brake handle was squeezed but was always bright and steady when the pedal was pushed, now neither work.

I removed the tail light to expose the wires behind and I used my multimeter since the tail light works I measured the voltage of the brown wire which is the brake light wire. It reads .2 volts when either brake is applied.

I have lowered the bike 2" in the back and though maybe I chaffed the wire or damaged it somehow. So I removed the seat to expose the wires running on top of the fender. I found the brown wire and used a razor blade to shave back the insulation and tested the exposed copper wire. Again it read .2 volts when the brake was applied. So Now I'm lost. All the fuses are good. I don't think it's bad contact in the switches. I find it hard to believe that at the same time both switches suddenly failed to light. Anything I'm missing.
I want to get this resolved tomorrow if possible since the weather will be nice.

[gotjeepzj]

Hey also which filament lights for the tail light? The upper, or lower?

[Steve]

First of all, what are you using for a ground reference point for your multimeter? Best point is the negative side of the battery. If you find that you have your 12 (+/-) volts when grounded to the battery, you might have a GROUND problem at the tail light, not a POWER problem.

The tail light will light, even with a bad ground, by grounding itself through the brake filament. However, when the brakes are applied, the tail light filament now has 12 volts on both sides, so it goes out. If you have the choice of not turning on the tail light, you would see that the brake light would not appear very bright because it is really only turning on the tail light filament.

Check your brake voltage first with the meter grounded at the battery. If that works well, then move your ground point to the lamp socket. If you now have problems, tighten up all the mounting screws or run a separate ground wire to the housing.

If you have good lights with the pedal, but not the handle, clean the contacts at the handle or adjust them. There are two screws underneath that will allow the switch to move slightly to adjust the contact point. Just loosen them about a half turn or so, then slide the switch. If you happen to take one out accidentally, put it back in before touching the other screw. The innards of that switch are spring-loaded in the blow-apart position, and are just sitting there waiting for unsuspecting little ol' YOU to come along. :shock:



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[Steve]

You posted your second question while I was typing my book. Can't say whether it is the upper or lower filament. Remove the bulb from the socket, use a jumper wire and connect it to the battery to see which filament it is. If you read my book above, you will see that if you have a bad ground, both the tail circuit and the brake circuit will only light the tail filament, when applied separately. When applied together, the light goes out.

Just a rule of thumb when working with electric or electronic stuff:

IF IT'S DOING WEIRD THINGS, IT HAS A BAD GROUND.


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[Kcwiro]

Sometimes its easier to start with the basics... have you checked your stop light switch?...I only ask since the one in my hand grip broke and now my tail light doesn't always come on... the pedal always works and that switch is easy to figure out... silly yet have you tried replacing the bulb?

Maybe dumb... but sometimes checking the obvious can go a long way.... I know I've done it:-D

post your findings, my curiosity has been tripped

[brveagle]

my guess is that it's the brake light switch... They commonly get disconnected...

[gotjeepzj]

Thanks all. I'm unscrewed the ground from the assembly and have it mounted to the where the light assembly bolts to the bracket that holds the light on the fender. I didn't try another ground because the same ground is sufficient enough to get my proper reading on the tail light. I also grounded the meter to a ground in the electrical box and to the shaved exposd copper strands and got the same reading.

Yes I changed the bulb first.

I have tried getting a reading while applying both the handle brake and the foot brake together and independtly.

My main cause for concern is that it suddenly quit working.

[Kcwiro]

tried a continuity / tone (open/closed) test between power and the light? ... if you have a busted wire somewhere you should be able to locate where to look with that test... since as steve put it you probably have a ground issue.

just my .02

[gotjeepzj]

I'm still trying to understand. Why would I have a ground issue with the brake light and not the tail light? Both switches have to tie in together at some point so I'm assuming the problem lies there

[gotjeepzj]

I'm going to go explore the grounding issue now. How do you check the contacts for the pedal switch? I'm assuming that there would be power going to one side of the switch at all times and when the switch is closed the power would then flow to the tail light correct?

[Kcwiro]

I would find where it makes contact with the wires and just short the connection with a piece of wire...then you can work on it from there and work back.

I won't make an attempt to explain the grounding part since it seems odd even to me but each circuit needs a + and a - .... one absent of the other well ... nuttin

[gotjeepzj]

I discovered where the rear brake switch was and when you press on the lever the plunger dosn't move at all. I haven't removed it yet, but here is my theory. When the plunger pulls out it should complete the circuit and activate the brake light.

Fine if that's the case and the plunger is already pulled out the the brake light should be on all the time correct?

[gotjeepzj]

](*,) I'm an idiot.

I thought the tail light was always on when the key was turned to on. What I thought was the tail light was the brake light. After I discovered the plunger wasn't moving I disconnected the wires and voila the light went out. I then turned on the headlight switch and finally the upper filament lit. I then turned the headlight switch off and squeezed the front brake lever and got the same sporadic lighting on the brake light which as I said has always been normal.


That being said is that switch cleanable/ rebuildable or is it a boneyard part?

[chef1366]

](*,) I'm an idiot.

I thought the tail light was always on when the key was turned to on. What I thought was the tail light was the brake light. After I discovered the plunger wasn't moving I disconnected the wires and voila the light went out. I then turned on the headlight switch and finally the upper filament lit. I then turned the headlight switch off and squeezed the front brake lever and got the same sporadic lighting on the brake light which as I said has always been normal.


That being said is that switch cleanable/ rebuildable or is it a boneyard part?

Check Ebay. I see them all the time.
We are idiots at one time or another so don't feel bad. If you only knew some of the things I've done:shock:

[QuaiChangKane]

+1,000 for the brake light switch.


But to clarify, are you having problems with both the brake light for both the front and rear brakes?


The rear switch is a plunger switch, which is adjustable. The front switch is a sliding switch, which is non-adjustable (IIRC - I've swapped mine out). The contacts on the slider-portion of the switch can get worn and corroded. If you look underneath your front brake lever, you'll see where the wires go into the housing underneath a little cover. Remove the two screws for that cover very carefully, as there's a spring inside. Remove the spring and the slider, then spray some contact cleaner on the contacts inside the brake lever housing, and clean the slider contacts as well using some emery cloth. Apply no-ox grease to both contacts and reassemble. Not too much grease - just a small amount to cover the contacts - too much can attract dust. I believe there's a gasket under the cover as well, make sure that's in good shape to keep moisture out.


The spring can wear out and the slider can corrode or wear through easily. It's a poor design for a switch. I've swapped my controls out with newer Katana controls which use a sealed plunger-type switch. Drastic improvement, IMO.


Good luck, and if your rear brake doesn't engage the brake light, do try to adjust the plunger, along with checking the contacts. I'd check your switches before the wires, connections, or bulb housings - in that order.

And I believe your tail light should be on all the time, even on bikes where you can turn off the headlight.



-Q!