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john.b.watts
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VBMWMO #8877
Joined: 03/09/2015
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Bike is a '59 R69 undergoing full restoration with a Powerdynamo 12v conversion. Tested the lighting and all works great - running, headlamp, dimmer switch for high and low spot on, tail light, brake, etc. just great. No complaints.

However, the speedo. bulb will not light. I have tested the socket body and bulb wire against the battery and the bulb lights up just fine. I have run a lead from + and grounded the socket body on known ground points on the bike (chassis, engine) and the bulb lights up. BUT, when I put that ground against the speedo body, or any metal WITHIN the headlamp shell I get nothing. Even when I use terminal 31 as a ground and 56 is live, I do not get the light to go on (known good from - terminal to 31 to - terminal and no issues).

At this point I have to wonder if there is corrosion resistance, though I have two socket bodies and both react the same way. I understand that 31 all the way to the - terminal at the battery is not a headlamp shell ground, but a selective ground whose white wire to the bulb socket assembly guarantees a solid ground.

Has anyone experienced this with a rubber-insulated headlamp shell for which you must make allowances? At this point, I would replicate the 31 wire to the headlamp socket body for the speedo socket body to guarantee a ground as I cannot figure out any way to do this otherwise. What am I missing here?

schrader7032
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VBMWMO #7032
San Antonio, TX
Joined: 10/27/2006
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I'm not that good with DC

I'm not that good with DC electrics, but from looking at the diagrams, it seems that the bulb grounds to the headlight shell. That means that the headlight shell must be connected to the frame somehow. The shell if floating, held in place by the bolts through the sides but it is also isolated by rubber washers. I would think that this connection to the frame needs to be inspected. It would seem then that the bolts are the path to ground.

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'78 R100/7 '69 R69S '52 R25/2

john.b.watts
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VBMWMO #8877
Joined: 03/09/2015
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You are surely correct about

You are surely correct about the rubber - we have the rubber on the backside of the headlamp shell "ears" against the fork, and the four round rubber "washers" on either side of the shell itself. Schematic shows a ground via speedometer body to headlamp shell, but from there where is my shell to chassis ground? I have been looking for this and can only assume you are correct and it is assumed a ground is achieved from the shell to - terminal post via the shell itself.

Twocams
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VBMWMO #8750
Joined: 03/16/2014
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Thanks for the problem reply

Thanks for the problem reply John, I had back on 8-17. My problem was the head light. Picked up a ground and everything has been great. But also put a note inside the head lite bucket to self. How and where I got the ground. For trouble shooting if needed. My brown ground wire is neatly put under the gas tank with others. So was never in the directions I needed it.....

twocams

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Twocams
69 R69S 03 K1200GT
92 R100RT

wa1nca
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VBMWMO #8374
Ashfield Ma.
Joined: 09/27/2012
Posts: 421
Speedometer ground

The ground path for the speedometer is completed by the speedometer cable for the night light in the speedometer

I tested 5 cables
3 had continuity from one end to the other
The last 2 I bought had no continuity from one end to the other and I also had to add a separate ground to make the light work

I never would have guessed the the cable also provides the ground for the speedometer

The only solution is to add a separate ground
Small wire from #31 to speedometer shell

I bought mine from a well know source here in the USA

Tommy

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Tommy Byrnes
54 R51/3 55 R50 64 R27 68 R69US 68 Sears Allstate 250 (Puch)

john.b.watts
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VBMWMO #8877
Joined: 03/09/2015
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Wow, I would not have thought

Wow, I would not have thought of that at all - thank goodness this group is available for this sort of corner case!

I will test and install the cable and see what is what - many thanks!

wa1nca
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VBMWMO #8374
Ashfield Ma.
Joined: 09/27/2012
Posts: 421
Speedometer cable

Ill bet your old cable has continuity from one end to the other and the new one doesn't

The new ones I tested had the insulation crimped to each end were as the older cables insulation is sripped off and then crimped to provide the path to ground via the speedo shell to the transmission

Let us know if you find the same

Tommy

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Tommy Byrnes
54 R51/3 55 R50 64 R27 68 R69US 68 Sears Allstate 250 (Puch)

john.b.watts
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VBMWMO #8877
Joined: 03/09/2015
Posts: 42
It was the speedometer cable

It was the speedometer cable - or the lack of it! Once I tested the cable (continuity good end to end), I installed it and the speedo. lamp came on with the switch over to Hi/Lo headlight. Many thanks for the guidance on this to everyone.

hooverbj
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VBMWMO #9255
Joined: 04/01/2017
Posts: 104
My speedometer wasn't

My speedometer wasn't grounding either. I was considering borrowing the ground from the headlight, but didn't want to create a clusterf#!k of wires every time I opened the headlight shell, so I ran a seperate 16 gauge wire from the transmission up along the frame as a solution. I didn't have the patience or the funds to try 15 different kinds of speedo cables.

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