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Brake light wiring question

willie

willie

Forum Mentor
Past Site Supporter
This is a 2 part question but I'd like an answer to the 1st part, for now. I would like to know why I have about 6 volts going to the brake light before I squeeze the brakes. That 6 volts rises to battery voltage (approx. 12.2V) when I squeeze the brakes. The voltage is across the white wire and ground (B/W) wire, located about 10" from the taillight. FWIW, the harness is OEM.
I'm asking cause I find this kinda odd.
Thanks,
Willie
 
Presuming this is on the 1100G? :-k

What is your voltage on the second fuse in the box? That is the SIGNALS fuse, which powers the brake light circuit and a few other things.

If you have good voltage there, follow the wire to the connector at either brake switch and check again.

Do you have a brake light installed? What is it doing while you are getting these measurements? For example: does it look dim (not counting the tail light (pull the LIGHTS fuse to be sure)), then brighten up when you apply the brakes?

What is the voltage from the white wire to the negative terminal of the battery? If that is better, you have a bad ground wire (the black/white on you were checking with earlier).

.
 
Thanks for responding. I've answered your questions below. I think you'll share my surprise with the findings.

Steve said:
Presuming this is on the 1100G? :-k Yes. Sorry bout that

What is your voltage on the second fuse in the box? 11.52That is the SIGNALS fuse, which powers the brake light circuit and a few other things.

If you have good voltage there, follow the wire to the connector at either brake switch and check again. Here's where it gets even stranger :eek: I have 3.8 V across the brake switch leads at the rear brake with the ignition on. That voltage DROPS to .40V when I apply the front brake.

Do you have a brake light installed? Yes What is it doing while you are getting these measurements? For example: does it look dim (not counting the tail light (pull the LIGHTS fuse to be sure)), then brighten up when you apply the brakes? Yes. Its on when the ignition is ON and with the Headlight fuse removed. It brightens just a little when the brakes are applied.

What is the voltage from the white wire to the negative terminal of the battery?11.52 with ignition OFF, 4.19 when ignition is ON and drops to .92 when the brakes are applied. If that is better, you have a bad ground wire (the black/white on you were checking with earlier).
.
Click to expand...
Glad its not riding weather. Its about 36 and raining as I type this.
Thanks,
Willie
 
willie said:
What is the voltage from the white wire to the negative terminal of the battery?11.52 with ignition OFF, 4.19 when ignition is ON and drops to .92 when the brakes are applied.
Click to expand...
If you have 11.52 volts from the white wire to a battery ground with the ignition switch OFF, you definitely have some problems.

By "ignition OFF", I am presuming that you mean the KEY is off, not just the 'kill' switch? :-k

.
 
Steve said:
If you have 11.52 volts from the white wire to a battery ground with the ignition switch OFF, you definitely have some problems.

By "ignition OFF", I am presuming that you mean the KEY is off, not just the 'kill' switch? :-k
.
Click to expand...

You presumed correctly but reminded me of something I forgot to mention. I had the kill switch in the OFF position at all times (regardless of whether or not the key was in the ON position).
And I agree, I definitely have some problems. With the bike as well. :)
 
Sorry about your problems, let's concentrate on the bike for now, OK? :p

That white wire should not have any voltage on it when the key is in any position except ON.

Remove all the fuses, check voltage on the white wire with the key OFF.
Install the MAIN fuse, check voltage.
Keep adding one fuse at a time until you find which one powers the white wire.

.
 
willie said:
This is a 2 part question but I'd like an answer to the 1st part, for now. I would like to know why I have about 6 volts going to the brake light before I squeeze the brakes. That 6 volts rises to battery voltage (approx. 12.2V) when I squeeze the brakes.
Click to expand...
Another thing that may cause the voltage readings you are seeing is, corrosion or some form of conductive substance in the switch.

I once was testing for excessive current draw on an old Buick 225. I measured somewhere about 11 volts at the starter terminal. Given the fact it used an external starter solenoid between battery cable and the starter, it should have been cranking continuously given the voltage measured.

One of the down falls of using a Digital Volt Ohm Meter is its very low current draw. Had I used an old analogue volt meter or a test light to measure the voltage instead, I would have not been chasing my tail.

A little path of resistance inside the solenoid was all it took.

Try using a small test light.
 
Thanks for the advice and suggestions. I'll get back to it in a few days. I admit to being a puss when it comes to working in the cold. I was okay today with it being in the hi 30's but tomorrow is supposed to peak at 20. A little too cold, IMO, to be working in an unheated garage. I'll post an update when I get back to it. Thanks again,
Willie
 
Kill switch is in the ignition and starter solenoid circuit. Should have no effect on the brake light circuit.

QUOTE
Here's where it gets even stranger :eek: I have 3.8 V across the brake switch leads at the rear brake with the ignition on. That voltage DROPS to .40V when I apply the front brake.
END QUOTE
Nothing strange about the voltage going to near zero.
If you are measuring voltage ACROSS the rear brake swtich (one meter lead on one side of switch and other lead on other side of switch), that would also be across the front brake swtich since they are in parallel. And when activate either swtich the voltage acraoss it/them should go to about zero, and then all voltage be across the tail light.

What is strange is that it is not much closer to battery voltage when measure across the switch. I suspect a problem between the fuse and the switch.

Measuring votage ACROSS a swtich is an advanced troubleshooting technique that is not so easy to understand.

Try measuring voltage AT the switch (one lead on switch, other lead to ground or batt negitive). Much easier to understand.

.
 
willie said:
Thanks for the advice and suggestions. I'll get back to it in a few days. I admit to being a puss when it comes to working in the cold. I was okay today with it being in the hi 30's but tomorrow is supposed to peak at 20. A little too cold, IMO, to be working in an unheated garage. I'll post an update when I get back to it. Thanks again,
Willie
Click to expand...


It is too cold for the wires to push electricity through. :) I have the same problem in my home garage

When spring weather returns the light will work magically - or I'll help by installing a big red wire from the hot side of your coil down to the taillight bulb - BINGO taillight. :eek:
 
trippivot said:
It is too cold for the wires to push electricity through. :) I have the same problem in my home garage

When spring weather returns the light will work magically - or I'll help by installing a big red wire from the hot side of your coil down to the taillight bulb - BINGO taillight. :eek:
Click to expand...

Of course! Duh! Why didn't I think of that. Now as far as running the extra wire to get the taillight to work. That one works okay, its the brake light that I'm having issues with. Ah, what the h*ll. Brake lights are soooo over rated. The guy behind me will surely see that I'm slowing down. If he doesn't, chances are that he wouldn't see the brake light either. Perfect! Problem solved. I'm so glad you responded. :D
 
Make certain that the correct bulb is installed and that it is making contact correctly. I have had crosstalk between the tail light and brake light becayse of bad/incorrect bulbs and or sockets. I would also clean all the wet crud out of the front switch. You have another problem besides that, but doing those checks may help you find it.
 
850 Combat said:
Make certain that the correct bulb is installed and that it is making contact correctly. I have had crosstalk between the tail light and brake light becayse of bad/incorrect bulbs and or sockets. I would also clean all the wet crud out of the front switch. You have another problem besides that, but doing those checks may help you find it.
Click to expand...

Good thinkin Combat. I know the bulb is correct but will make certain the front switch is good and clean. Should be already but worth a look to eliminate that as being the culprit. I'm also planning on disconnecting the front switch to see if it has any effect and then the rear switch. I'm looking forward to finding the source of the problem. Stay tuned.
 
I usually heat the garage when I work on the bikes.
I even start them in the garage, after it is warmed up.

(Then I move them outside to continue running them, obviously.)
 
Well guys, I have solved the mystery and thought you'd like to know what I found. Turns out I left out a key bit of information. I'd forgotten that I had replaced the rear taillight bulb (1157), with an LED unit. In fact, I forgot all about it until I removed the lens this afternoon and discovered it. I replaced it with a conventional bulb and everything returned to normal. THANK YOU one and all for your suggestions and advice. I also have a much needed clean front brake light switch ;)
Willie
 
willie said:
Well guys, I have solved the mystery and thought you'd like to know what I found. Turns out I left out a key bit of information. I'd forgotten that I had replaced the rear taillight bulb (1157), with an LED unit.
Click to expand...
Actually, you still have a problem. :eek:

Merely installing an LED replacement whould not cause any problems.

We have an LED replacement in my wife's bike, have had NO problems with it.

.
 
Well that's not good.:( I prefer to think that the cheap-assed LED was causing a problem by "bleeding" voltage over into the brake light circuit from the running light circuit. Support of this idea is that, with a conventional bulb in place, there isn't any voltage present when I measure across the wires going to the brake light with the ignition turned on. Also, the 2nd filament lights up only when the brake switch is activated. Thoughts?
Willie
 
willie said:
Thoughts?
Click to expand...
Might be your "cheap assed bulb".
icon_shrug.gif


Maybe try another LED 'bulb'? :-k

.
 
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