Fog light electric issue

[camos]

Got a strange one here, at least to me anyway. A few of months ago one of the fog lights on my bike would be slow to start when turned on while the other one lit immediately. After a few weeks the slow light stopped working. As a test I replaced it with a spare light and it worked. Assumed it was just a faulty bulb and began using the spare rather than find the problem with the original one.

 

Fast forward a couple of months and that spare light started getting slow to start too and after a week or so it also stopped working. Today I checked the voltage across the two supply connections which was about 13.5 at an idle. Plugged one of the connections back into the light and checked the voltage across the supply line and the light line and it was the same 13.5.

 

Seems to me power at the supply line but no light would indicate a burnt out bulb or some other internal circuit issue. If the bulb were burnt out there should have been no voltage indicated with the second test.

 

Didn't have time to open the light up to check further.

What am I missing?

 

The bulbs used are yellow H3's which are not readily available around here. I could try a white H3 but I'm going to order a set of HD H3 bulbs and give them a try so I didn't want to pay for a bulb that would not see much use.

[mbrood]

You have voltage on one side, but do you have a good GROUND on the other?

 

Also, a corroded or damaged connection on the b+ side will limit the current so even though you have 12v, you can't pump enough current to light the light.

[camos]

I had considered that a problem with the ground could cause the light to not light. Since the other light was working it did not seem certain that was the cause. I can't think of any other cause than what you suggested though.

 

The lights are powered through a relay with a two wire circuit to the battery. If there is a ground problem it would likely have to be where they connect before running back to the neg bus at the battery.

[BOO]

I had considered that a problem with the ground could cause the light to not light. Since the other light was working it did not seem certain that was the cause. I can't think of any other cause than what you suggested though.

 

The lights are powered through a relay with a two wire circuit to the battery. If there is a ground problem it would likely have to be where they connect before running back to the neg bus at the battery.

 

Since this is not a common problem to both lamps I would check all the terminals/connections from the relay to the lamp. I don't recall how the lamps are connected to the wiring but I believe they are screwed to the lamp, if not then I would check the plug real good as well as any other plugs you have on the wires AND any terminal connections. (read crimp on types)

Good Luck,

BOO

[mbrood]

When changing a light "temporarily" fixes the problem... it's possible that your jiggling things around made a temporary "better" connection. You can always run separate hot wire to the bulb and prove if the grounds are good.

[camos]

When changing a light "temporarily" fixes the problem... it's possible that your jiggling things around made a temporary "better" connection. You can always run separate hot wire to the bulb and prove if the grounds are good.

Great idea, I'll hook the light up directly to the battery and see if it works then go from there.

 

Since this is not a common problem to both lamps I would check all the terminals/connections from the relay to the lamp. I don't recall how the lamps are connected to the wiring but I believe they are screwed to the lamp, if not then I would check the plug real good as well as any other plugs you have on the wires AND any terminal connections. (read crimp on types)

It is not just common to two lights but to two sets of lights. The original set did the same as the set that replaced it. The same side went out on both which would indicate the problem is likely in the wiring or connectors on the same side. The first check though will be the direct hookup as mentioned above. If the direct hookup works then I expect I will have to trace the bad side back to where it connects to the other side before connecting to the relay.

 

Very simple when it all gets sorted out logically.

Thanks a bunch for your input.

[DanC]

I would run an external positive line and ground directly from the battery outside the bike and attempt to operate the light with direct power. Elimiate whether the problem in the ground circuit or the positive side. Then you can check back by opening the orginal circuit and using the test voltage directly from the battery. This test WILL lead you to the problem. Just because one has 13.5 volts does not mean that you have current. Current equals Voltage over resistance. Sorry but I have years of electronic schools behind me so if I get to far out there please forgive me. :dancefool:Hope that this helps. DanC

[camos]

When I tested it I did just what you suggested DanC. Turned out to be the bulb. The filament appeard sound but there was discoloration around the base that indicated heat. Must have been just a coincidence that two lights on the same side went out in the same manner.

 

Thanks for the suggestions.

Help is always appreciated.