New taillight blows fuse all day

Hey all. I installed a new taillight today but keep blowing the fuse. I have no problems with the light working fine as a running light, but when I apply the brake I blow the 10 amp fuse. I am also using the original light bulb with the new set up (figured this would help make things easier). The new light is grounded by the chassis, so I soldered a wire from the bulb housing to the ground and have made sure that the blue and yellow ( taillight and brake) wires are connected correctly to the harness (if connected the opposite way the brake lights up when running). I keep blowing the fuse when I apply the brake. All help is appreciated!

 

Does it blow the fuse with either the front or rear brake application? Most likely is that something is shorting, mechanical parts that wear are the more likely candidates, like a brake switch.

 

I mostly tested with the front brake. I will add that the original brake light worked fine, and will again if i hook it back up.

 

Pinched wire in new assembly? With the bulb removed and the blue and yellow wires unplugged, do you get continuity to ground on either wire? If you do, you've got a short.

 

How can I test Gamuru? I am sure I do not as the setup is almost exactly the same as original. I basically unhooked the old, and re routed wires and mounted the new. Only difference I can see is the new light fixture grounds through the chassis. Since it grounds through the chassis should I use the original ground wire? I am now, grounding to the metal light housing.

 

Do you have a continuity tester? Or a test light?

 

Phil, if this keeps being a stumper, feel free to do this. When Paul comes over as we discussed, or when you talk with him, he could call his brother Glen, a master electrician (lives in Manchester but works in your area) who also knows some about bikes. Glen may have an idea.

A bit complicated perhaps, but if you're really frustrated might be worth a try. They're both really nice guys and you're about due for a good break.

let me know how it turns out (PM?)

good luck,
gene

 

Pinched wire or just a generally poor quality/defective new rear light unit.

A rear brake light draws about 70W when braking, divided by 12V is a little less than 6amps, so a 10A fuse has plenty of headroom.

Since it works as a running light, we'd have to assume that the ground is okay (since the running and brake light are sharing a common ground, thru the chassis).

When you use the brake lever or pedal, does the brake light even light up before it shorts? If not, then the short is in-between the brake switch and somewhere before the bulb.

Checking it via the front brake lever and then the rear brake pedal only might help isolate the problem.

Also, once you get the problem resolved, I would suggest hooking up and adapter wire to go from the "chassis ground" back into the original black ground wire in the factory harness. Just my preference. Don't like chassis grounds.

 

Chacal

I have grounded to the original harness ground. The taillight comes on upon turning the key, then as soon as I apply the front brake the brake light comes on for about a second before you hear the fuse pop. I do not get a brake light at all when applying the rear brake. As stated before, the original light worked fine, I am even using the original bulb. Maybe a second set of eyes will help.

The new light is a 12v brake/tail light from the auto zone down the road.

Gamuru - I have both.

 

Ok hopefully someone can help. I replaced the light with another stop/tail light. This one blew 1 fuse. After replacing the fuse the taillight comes on but the brake light will not work until the bike runs for about 5-10 minutes.

Any suggestions will be appreciated.

 

But it works fine with the stock light? I'd find another light manufacturer.

 

those things are coincidence, one or both switches is shorting to earth, disconect both switches, touch the ends of the two wires together, if the bulb works, it's the switch, if it still shorts trace the wires back & make sure nothing is touching the frame.

 

Let's start with the light assembly. With the bulb removed from its socket, test for continuity between the ground wire and the blue wire, between the ground wire and the yellow wire, and between the yellow wire and the blue wire. All should be open (∞). If not, you've got a short somewhere inside the housing.

With an 1157 light bulb installed, the resistance should be about 6Ω on the yellow wire (brake light) and 14Ω on the blue wire (running light). Measure the resistance between the yellow wire and the ground wire and the blue wire and the ground wire. They should be similar to the above figures. Finally, measure the resistance between the yellow wire and blue wire. This should show a resistance of about 20Ω (R1+R2).

If all of this checks out, the problem is with the wiring harness on the bike. Let us know where you end up.

 

This isn't any help to Phil (who's a good guy, BTW) but I gotta say it...

1, I have an 81 XJ 650H; don't know electrics; certain to need help someday

2. Gamuru has same bike; knows everything electric; is generous in sharing


Any debate that Heaven can provide protection for the needy and clueless?

Didn't think so.

 

Thanks! Just doing my part.

And you all can do your part. Donate today to help Sno keep this site up and running.

 

Gamuru

That is awesome info, I will test this today (after I get outta work!) and will keep all updated with a response tonight.

Thanks again.

 

With a multimeter you won't measure this much resistance. Until the filament heats up resistance on an incandescent bulb is real close to 0.

**EDIT**

I got off my backside and ohmed one out. The values are .7Ω and 2.4Ω

 

Yep, I checked a Wagner bulb off the shelf at work today... .6Ω and 2.0Ω.

 

I rode about 75 miles yesterday and brake and tail light worked.