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Discussion Starter #1
Hello all,

I've spent the better part of the day trying to install my new Maund Lucas tail light. The LP marker lights are working properly (finally). The brake light is working, but the tail light will not come on. Here is what I have:
  • Maund Lucas tail light
  • Lockhart Philips Marker lights (extra wire for running lights, I'm not connecting it and it's been sealed off)
  • NB rear tail/signal light harness
The tail light has a black and red wire. Red wire of the tail light goes to the red wire of the harness and the black wire to the blue wire of the NB harness. I attached the ground of the harness to the battery while testing. I keep blowing the 5 amp fuses for the tail light and instrument lights. For ****s and giggles I replaced both 5 amp fuses with 10 and the instrument cluster fuse still blew. Even if that had worked I couldn't leave them in there. I'm thinking a bad ground,but I'll be damned if I can figure out where. Shouldn't wiring it to the battery be the best ground you can have, or is that a no, no for lights?

I'm at a loss. Can anyone help?
 

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A bad ground won't cause a fuse to blow. A bad ground or high resistance in the ground is an open. You have the hot wire going directly to ground somewhere most likely before it reaches the bulb. Shorts to ground blow fuses.
 

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Trace the wires carefully looking for a pinched wire somewhere. Most shorts are caused by pinching a wire and causing the insulation to break and allows the wire to touch ground. Also piercing wires runs a close second to pinching them. Ever seen a car with a dim headlight on one side? That's what a bad ground will do.
 

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Discussion Starter #5
I checked again last night and couldn't find a pinched or exposed wire. As well this started happening while all the wires were stretched out & I was figuring out the connections.

Not a bad bulb as I've tried two and a bad bulb shouldn't keep blowing the fuses.

This has really got me bummed out as I want to use this new tail light assembly but I'm considering replacing the stock. :(
 

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Is it possible that something is wired wrong? That would be the only other thing I could think of. Something is allowing current to flow directly to ground BEFORE the load- which is the bulb. A short to ground after the load would just be fine as the circuit must return to ground at some point. Hope you find the issue. Shorts can be tough to locate sometimes but are relatively straightforward as far as the technical aspect goes.
 

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Discussion Starter #7
Is it possible that something is wired wrong? That would be the only other thing I could think of. Something is allowing current to flow directly to ground BEFORE the load- which is the bulb. A short to ground after the load would just be fine as the circuit must return to ground at some point. Hope you find the issue. Shorts can be tough to locate sometimes but are relatively straightforward as far as the technical aspect goes.
Well there are only 3 wires. One is a ground with a connector on it to be grounded to the frame or some such thing (I chose the battery for testing) and two other wires going into the tail light. Get those two wrong and it just doesn't work.

Very confused and disappointed with this whole thing. :confused:

Thanks for your feedback Fordtech.
 

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Well there are only 3 wires. One is a ground with a connector on it to be grounded to the frame or some such thing (I chose the battery for testing) and two other wires going into the tail light. Get those two wrong and it just doesn't work.

Very confused and disappointed with this whole thing. :confused:
Grounding direct to the battery is as good as any other method and makes no difference.

I take it that you had the lens off the Lucas light and the bulb out during fitting? If so, check out the little contact board at the bottom of the bulb holder. It is possible for the spring to push this out, and in replacing it, it becomes rotated. There should be a small tab on it that engages in a groove in the side of the bulb holder, which gives it correct orientation, but the tab is such a loose fit in the groove. Also make doubly sure that the spring is clear of the contacts, since this could ground one of the bulb filaments, blowing the fuse. Hope this helps, there have been a couple of these cases on here just recently.
 

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Discussion Starter #9
Grounding direct to the battery is as good as any other method and makes no difference.

I take it that you had the lens off the Lucas light and the bulb out during fitting? If so, check out the little contact board at the bottom of the bulb holder. It is possible for the spring to push this out, and in replacing it, it becomes rotated. There should be a small tab on it that engages in a groove in the side of the bulb holder, which gives it correct orientation, but the tab is such a loose fit in the groove. Also make doubly sure that the spring is clear of the contacts, since this could ground one of the bulb filaments, blowing the fuse. Hope this helps, there have been a couple of these cases on here just recently.
This was a great idea and I ran right outside to try it. Unfortunately it was not the answer . There were two tabs on the contact board that were really indistinguishable, so I tried it both ways and both made the tail light fuse blow.

I'm headed out now to re-replace the harness and the light unit.
 

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Discussion Starter #10
Ended up putting the original harness and OEM stop light back in place. I hate to do it, but I just may take the bike and light in to my mechanic to have it done. Let him have the headache of trying to find an electrical fault!

Thanks everyone for offering your advice

Steven
 

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Ended up putting the original harness and OEM stop light back in place. I hate to do it, but I just may take the bike and light in to my mechanic to have it done. Let him have the headache of trying to find an electrical fault!

Thanks everyone for offering your advice

Steven
You need to use a volt-ohm meter to check each wire in your harness for a short. Otherwise your just going in circles.
 
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