Tail lamp wiring

Hi all - Finishing up wiring on my 72 750 Roadster - new main harness. The harness has three leads for the tail light unit itself - power, earth and stop lamp. The tail light itself is an Emgo unit as supplied with the Old Britts cast aluminum unit. It has only two leads - power and earth . I am unsure as to what to do about the stop lamp wiring .
Any help would be appreciated -
Thanks again for babysitting the electrically challenged one -RT

It's possible that the wire you think is ground is one of the filaments and that ground is the case (screws in the back). Take the bulb out and check that it has 2 terminals on the base. If only 1 then it doesn't have a stop lamp.

Richard Tool said:

Hi all - Finishing up wiring on my 72 750 Roadster - new main harness. The harness has three leads for the tail light unit itself - power, earth and stop lamp. The tail light itself is an Emgo unit as supplied with the Old Britts cast aluminum unit. It has only two leads - power and earth . I am unsure as to what to do about the stop lamp wiring .
Any help would be appreciated -
Thanks again for babysitting the electrically challenged one -RT

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The tail light probably has one lead for tail and one for stop. The housing is supposed to be the ground. On Triumph and BSA, the frame is a ground. On Norton, it's not specifically a ground. So, run a red wire from some bolt that holds the rear fender on to some red wire in the harness. That will make sure that the rear fender, and thereby the tail light housing is grounded.

Post a picture of the tail light if it doesn't work - lot of guessing here.

Thanks everyone for the help - I soldered up a jumper with a bullet on one end and ring terminal on the other. Ring around housing mounting bolt and and bullet to earth in main harness.
Black from tail light to harness tail lamp and red from tail light to harness stop lamp . I think I’ve got it now - RT

marshg246 said:

The tail light probably has one lead for tail and one for stop. The housing is supposed to be the ground. On Triumph and BSA, the frame is a ground. On Norton, it's not specifically a ground. So, run a red wire from some bolt that holds the rear fender on to some red wire in the harness. That will make sure that the rear fender, and thereby the tail light housing is grounded.

Post a picture of the tail light if it doesn't work - lot of guessing here.

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This. The aftermarket Lucas-replica cast alloy taillight is case-grounded. I have one bolted to the rear fender of the SS clone with no separate grounding.

To be clear the ground jumper I made up is unseen- it runs between the lens housing and the casting. Since the main frame is powder coated I removed the powdercoat at two points where the main harness grounds attach - one at the boss on the backbone where the original head steady rubbers where fastened and one behind right foot plate . I didn’t trust the fender / tail light casting as a good ground because of the powdercoat on frame and fender brackets and the rubber gasket under the tail lamp casting - hence the jumper being plugged into the harness ground.

Richard Tool said:

To be clear the ground jumper I made up is unseen- it runs between the lens housing and the casting. Since the main frame is powder coated I removed the powdercoat at two points where the main harness grounds attach - one at the boss on the backbone where the original head steady rubbers where fastened and one behind right foot plate . I didn’t trust the fender / tail light casting as a good ground because of the powdercoat on frame and fender brackets and the rubber gasket under the tail lamp casting - hence the jumper being plugged into the harness ground.

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Standard Norton Commando wiring has no specific frame ground. The red wires under the tank go to the head steady to head bolt on the timing side.

If you still have the Zener, then the Z-plate may provide a ground if you removed the powder coat between it and the frame, iffy. If you have a ground in the headlight shell, it may ground the frame, again iffy. If you still have the bridge rectifier, then that may provide a ground, again iffy. You'll always find the frame grounded through the clutch cable, but that's really iffy.

If you have those red wires to the frame instead of under the bolt holding the head steady to the head, your engine is grounded by the clutch cable only - not good!

When I wire Nortons, there is no Z-plate ground because there is no Zener. There is no bridge rectifier ground because there is no bridge rectifier. There usually is no direct headlight shell ground because new headlight shells don't provide one.

I run a red wire to the tail light no matter what kind of tail light and connect it to any convenient red wire in the harness.

No zener - Podtronics R/R - unused zener feed blanked off and zener ground run to z plate bolt at frame. Engine grounded with 14 ga jumper from head to frame with powder coat removed .

I always liked doing wiring. Crossover looks great too.

Bike is looking better than new, how bout a few more photos... Your work space is very well lit. I took most of my photos crawling on the floor in the back corner of my dad's unfinished basement...

Richard Tool said:

No zener - Podtronics R/R - unused zener feed blanked off and zener ground run to z plate bolt at frame. Engine grounded with 14 ga jumper from head to frame with powder coat removed .

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Looks good! The frame ground helps/hurts nothing and you have a good engine ground.

Richard Tool said:

No zener - Podtronics R/R - unused zener feed blanked off and zener ground run to z plate bolt at frame. Engine grounded with 14 ga jumper from head to frame with powder coat removed .

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Very pretty and clean. You've inspired me to clean up the wiring under my tank.

Thanks all for the help & compliments. I’ve just finished re wiring the WLA as the schematic supplied with the new Lucas harness is in error - see my post headed Warning Light Assimilator wiring .
( one of these days I’ll learn how to provide links )

NPeteN - I’ll take a few more pics and get them up in a bit - I’ll post them in my build thread as well as this .
Thanks for looking- RT

As requested here are a few more pics -