Grounding problem

Maybe you guys will have some ideas that can help me.

I have a three position ignition switch - off/ignition on/ignition and lights on.

With the switch in the "ignition on" position, my headlight is not lit. Unless I engage the front or rear brake. Then the headlight comes on.

Seems to be (?) the headlight is getting power through the brake lamp circuit. With power to that circuit cut off, OR the taillamp bulb out, the phenomenon stops. But restore power and put the bulb back in and I'm back to square one.

The taillamp has a good ground. I tested it with a multimeter, and even tried bolstering the ground wire by splicing in a new direct wire to a good ground. Made no difference.

Any words of wisdom will be most welcome. It's not a big deal, really, but it's annoying.

BTW I completely rewired the bike a couple years ago and this phenomenon just started recently, so something's changed.

Thanks folks - BrianK

BrianK said:

Seems to be (?) the headlight is getting power through the brake lamp circuit. With power to that circuit cut off, OR the taillamp bulb out, the phenomenon stops. But restore power and put the bulb back in and I'm back to square one.

Click to expand...

Have you tried another bulb?

Hi Les. Yes, but the problem remains.

BrianK said:

Yes, but the problem remains.

Click to expand...

Well, if it's not the ground and the bulb isn't the problem, are you sure you didn't do any work on the wiring or tail lamp prior to noticing this problem?
Maybe a short in the bulb holder but it's also a symptom of the tail lamp wires being connected wrong (wrong wire to ground)?

Did you check the tail lamp socket? Seems to me that the brake lamp circut is sistering with the running lamps. I've had the plastic/bakelite insulator that seperates the two deteriorate and when the bulb wes inserted the solder drops on the ends of the wires would marry. Pull the guts out of the tail lamp and give a check. Don't think the ground is an issue.


Tom

Les - Turn signals are grounded through their mounts, IIRC - only one wire (hot) to each?

Les/Tom, I'll take a look at the socket. I'm not following Tom's logic though - if the tail and brake lamp wires were connecting, wouldn't the brake light be on all the time (it's not - the headlamp seems to be getting power only when the brake lamp wire is energized). Thanks

BrianK said:

I'm not following the logic though - if the tail and brake lamp wires were connecting, wouldn't the brake light be on all the time

Click to expand...

As the headlamp is OFF at "ignition on" (no lights) presumably the tail lamp is also OFF, so there's no power reaching the tail lamp until you operate the brake light circuit. Somehow brake light current then appears to be passing along the tail lamp wire and grounding through the headlamp bulb causing it to light up.

Ah, got it. Thank you both. I'll report back.

Success!

Looking at the socket was the key. Something just didn't jibe... so I compared to the one I took off a while back (beat up but serviceable enough to save). Sure enough, the nice, shiny new aftermarket unit was WIRED INCORRECTLY. Cut two wires, switched (red to black/white, black/white to red), soldered, and shrink-wrapped them and we are good to go!

Yes, this means the problem began when I replaced the tail lamp unit a year ago...not a month or so ago when I finally noticed it....

Another frustrating problem solved. You guys were spot on. Thanks very much for your help.