Brake light issue

I have a crappy after market tail light that even though it's practically new. has had to be resoldered and practically JB Welded together what with all the cheap mounting pieces and subpar soldering and spot welds. This light has worked recently, but when doing my pre-ride check the brake light wasn't coming on, front or rear brake both. I replaced with a new bulb and no dice, just the running light is all that works. I've checked the ground, which reads at or near zero volts. I've wiggled wires and checked the connections under the tank, both brown and white wires and they seem OK. Show 11.9 V there. I've checked the white wire at the rear brake pedal and get no voltage.

I guess I don't know what I should be looking for really, and furthermore, maybe I'm not understanding the mechanism of the light itself. I should be getting a reading at the pedal, correct? In looking at the schematic, I can't tell if this is a straight route from the harness to the brake pedal or is the flasher unit junction/master switch somehow involved? It would seem if the running light is on, then the problem can't be the white wire or is the NG the power to the running light and the problem is one of the white wire circuits? I hate electrical, and I can barely read these damn things. Any help is appreciated.

I just can't believe those things only go for $15-20.

Me either. P.O.S. through and through.

Slup,

If you have voltage at the switch and the switch is working, the only thing that I can recommend is to check grounds via continuity (resistance) instead of voltage. Check first to ensure that the light housing is grounded. If not, you'll likely get no glow...

I once watched a friend trying to troubleshoot his tail light with the tail light assembly disconnected from the fender. He couldn't get any light. I just picked up the light and touched it to the frame while he was engaging the switch and the light came on. There was a learning point there someplace.

SteveMinning said:

Slup,

If you have voltage at the switch and the switch is working, the only thing that I can recommend is to check grounds via continuity (resistance) instead of voltage. Check first to ensure that the light housing is grounded. If not, you'll likely get no glow...

I once watched a friend trying to troubleshoot his tail light with the tail light assembly disconnected from the fender. He couldn't get any light. I just picked up the light and touched it to the frame while he was engaging the switch and the light came on. There was a learning point there someplace.

Click to expand...

Yeah, add a proper ground whenever possible. :mrgreen:

OK, made a little progress. I put a jumper to the ground and touched it to the frame and, voila, brake light. I tried it at the rear brake pedal, and it works. I pulled the brown wire on the wiring harness under the tank and it works there. Where should I be looking now?

And I failed to mention, when it lights up, I'm not even touching the brakes! Do I have 2 things going on here? Improper ground and something else?

1. So I can look at the correct wiring diagram what year / model are we talking about?

2. When you say you jumper to the frame what exacly did you do?

3. Electrons are fun to play with do not let them scare you.

Chuck

slupdawg said:

I put a jumper to the ground and touched it to the frame and, voila, brake light.

Click to expand...

Slup,

It's not clear to me what you jumpered to ground. The ground should already be grounded to the frame. You haven't indicated what year and model of bike you have. I think they are all very similar with regard to the brake light circuit but the following should be appropriate:

You should have two circuits controlling the brake light. One for the front brake and one for the rear. The wire from the front brake circuit should be brown, the wire from the rear brake circuit should be white. Each of these wires should connect the light to the power source through the front and rear brake switches. Each provides power to the lamp when each respective brake is applied. The ground is provided by the physical housing of the lamp assembly.

I would start by ensuring that the power is off and removing the brake light bulb. Once removed, I'd make a meter reading from the inside of the socket (the part that the bulb screws into, not the contact in the bottom) to ground. The meter should be on resistance (ohms). The meter needle should swing from infinity to zero ohms when you do this. If not, you've found at least one problem and you need to figure out why the lamp assembly is not grounded. It may be a wire inside the assembly that is supposed to lead to the housing of the lamp. I can't really tell without looking at it since it's aftermarket.

Once you've verified that the lamp assembly is grounded, start tracing the wires of the circuit that supply power. The best way to do this is to check continuity (resistance/ohms again) from the contact inside the socket (at the bottom of the socket) to each of the switches. There should be two contacts in the socket. One is for the tail light, the other is for the brake. Do not do this with power applied as you may short the circuits out with the probe. The idea is to ensure that the socket contact is physically connected to the switch.

If all of this checks out, then start tracing the voltage.

OK, I think I'd better start over, Chuck, because I've made a discovery here. First of all, it's a '73 750 Roadster. Secondly, the wire that I was thinking was the ground can't be the ground. I think the brake light assembly is wired backwards. Apparently the outfit that makes these cheap things has no quality control whatsoever, or the owner left for a long lunch break and put his worthless nephew, Ngo Gihva Fukee, in charge and he spent all afternoon making time with the girls on the assembly line.

Firstly, this light has 3 wires. I have since surmised the red wire is ground and leads to one of the 2 terminal ends that contact the bulb. The second (black) wire is also leading to the end of the bulb and must be power to the running light. The 3rd wire is a black and white stripe and is soldered (poorly) to a ring at the top of the socket assembly. I thought that it was the ground, but can't be. Duh.

So, what I did Chuck, was to disconnect the striped wire and jumper it to a nut on the z plate, and the brake light illuminated. So, apparently the crappy little thin wire with a poor soldering job conducts electricity. It did this without engaging either brake. It does not matter if I engage the brake at all.

SIDE NOTE: *I have a couple of jumper wires, both the same gauge, out of the same package, and yet one will illuminate that brake light FAR more than the other. Just an illustration of why I hate electrons, Chuck. I hate them very much.*

OK, so I call my go-to guy on my bike, and he says to pull the wires on my rear brake pedal. I take the test light and put one to the white wire and the other to the frame and it lights up. Then I take the tester to the brown wire and it lights up, too. He says that means the rear brake switch is bad because it shouldn't light up unless the brake is being depressed , but that just doesn't sound right. I am getting confused now and rather than think about this any longer today, I am putting some Trower on and getting blitzed. This gestation period will hopefully result in the bike magically fixing itself or someone telling me what to do. I have lttle faith in my own problem-solving abilities. Every time I get cocky, the old girl lets me know what my level of incompetence really is.

It's not clear to me what you jumpered to ground. The ground should already be grounded to the frame.

Click to expand...

Steve, you're right, that was what I finally concluded too. My scant ( and I do mean scant) electical knowledge includes knowing you put power to ground and vice versa to get a reading. I just never thought of it at the time.

Find yourself an electronics expert. Believe me it is most likely a grounding problem. If I were there I could find it in 3 minutes with my trusty Fluke. Maybe you know a Ham radio operator, he should be able to fix it, if he has any experience. Electronic circuits are not magic. You just need to understand how circuits work and once that happens, it all sorts out in short order, but as always on a car or m/c, the grounding is always an issue because mostly it doesn't exist (or worse intermittently exists) which is a big problem.

Dave
69S

DogT, well this guy I talked to knows his stuff, no doubt about it, but it's more likely my poor explanation of what's really happening and improper identification of the components that are suspect. If someone here doesn't have an idea, and I can't cypher it, then I'm sure he probably can.

Thanks,

Slup

OK, guess what I do not have a diagram for that year, but the diagram for mine (75 850) is wrong anyway. What I have and what you have sound the same. The brake/running light has 3 wires, in my case 1 red 1 brown and 1 brown/green this DOES NOT require frame grounding. Now my turn signals have only one wire to them and count on the plating of the plastic to be the ground, this it not your problem (yet). As I am rebuilding them as we speak I will run a lead to the metal housing and not count on the plastic plating.

So on to your problem.

3 wires to the light DO NOT worry about a ground.

Here is the test to do.

Lets see that the bulb and wiring work and go back from there. DISCONNET the 3 wires from the tail light. Hook one side of 12 volts to the RED wire (using the battery or battery charger) and then the other side to the Black wire , light should light. Then disconnect the from the Black wire and hook up to the Black/White wire, light should light. If not the problem is in the tail light assemble. If it works let me know and we will work backwords to find it.

One step at a time. Do not get a head of yourselve and go down the wrong road and get all confussed . This is how I used to train the techs.

Chuck