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what's going on ...or not. #735566
05/16/18 7:37 pm
05/16/18 7:37 pm
Joined: Aug 2009
Posts: 1,116
gastonia .. NC
L
limeyrider Offline OP
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limeyrider  Offline OP
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L

Joined: Aug 2009
Posts: 1,116
gastonia .. NC
I fitted a new wiring harness to my Dominator ...1966 650 SS ... the headlight, tail light, brake light and horn all work fine, the speedo and tach lights do not. I tested for continuity between ground and the bulb holder holders ... that is good ...until I turn on the lighting switch ... then there is no continuity ?.
When I turn on the lighting switch and use a piece of wire to " jump " between ground and bulb holders, the speedo / tach lights work ok ??. I'm not an electrician and this has me scratching my noggin.

Any and all advice is much appreciated.

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Re: what's going on ...or not. [Re: limeyrider] #735570
05/16/18 8:13 pm
05/16/18 8:13 pm
Joined: Mar 2006
Posts: 4,000
Norfolk, UK
L.A.B. Online content
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L.A.B.  Online Content
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Joined: Mar 2006
Posts: 4,000
Norfolk, UK
Originally Posted by limeyrider
I tested for continuity between ground and the bulb holders ... that is good ...


Was that with the bulbs fitted in the holders?



Re: what's going on ...or not. [Re: L.A.B.] #735578
05/16/18 9:00 pm
05/16/18 9:00 pm
Joined: Aug 2009
Posts: 1,116
gastonia .. NC
L
limeyrider Offline OP
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limeyrider  Offline OP
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Joined: Aug 2009
Posts: 1,116
gastonia .. NC
Sorry L.A.B., yes, bulbs in the holders. Taking the complete holder and bulb out of the back of the speedo / tach and touching a grounded surface lights the bulb ??

Re: what's going on ...or not. [Re: limeyrider] #735582
05/16/18 9:41 pm
05/16/18 9:41 pm
Joined: Mar 2006
Posts: 4,000
Norfolk, UK
L.A.B. Online content
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L.A.B.  Online Content
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Joined: Mar 2006
Posts: 4,000
Norfolk, UK
Originally Posted by limeyrider
yes, bulbs in the holders. Taking the complete holder and bulb out of the back of the speedo / tach and touching a grounded surface lights the bulb ??


You would normally do a continuity test using a meter set to 'ohms' and with no voltage in the circuit.
http://en-us.fluke.com/training/tra...ontinuity-with-a-digital-multimeter.html

So, if I understand correctly, with the lights switched on (so power is coming from the bike's battery) the bulbs light when touched to "a grounded surface" (whatever that particular grounded surface might be?) but do not light when attached to the instruments which suggests the instrument cases aren't grounded (rubber mounts?)

Or do the bulb holders have 'ground' wires? If so, what are they connected/attached to?


Re: what's going on ...or not. [Re: limeyrider] #735583
05/16/18 9:42 pm
05/16/18 9:42 pm
Joined: Aug 2001
Posts: 2,545
Oztralia
R
Rohan Offline
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Oztralia
Sounds like you need to add an earth wire to the bulb holders then ?
Or have I missed something, not personally knowing your bulb holders.

Earth return paths on some british bikes were less than optimal, shall we say.
Have electrons trying to negotiate the greasy steering head bearings was never a good plan ?
Not that Nortons would ever do that.....

Painted surfaces can also well insulate things that weren't intended to be insulated also !

Re: what's going on ...or not. [Re: limeyrider] #735593
05/16/18 11:11 pm
05/16/18 11:11 pm
Joined: Aug 2009
Posts: 1,116
gastonia .. NC
L
limeyrider Offline OP
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limeyrider  Offline OP
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L

Joined: Aug 2009
Posts: 1,116
gastonia .. NC
L.A.B. and Rohan, thanks for your replies.

The bulb holders do not have ground / earth wires, the instruments are mounted using two studs, the studs have a small rubber ring sandwiched between the back of the instrument case and the mounting plate which bridges the forks. The rubber rings were original pieces ... or so I'm told ....I have not been able to find them in parts manual though ??

Removing the rubber rings will remove any vibration dampening to the instruments, perhaps adding a ground / earth wire is the solution ?.

Thanks again for your comments.

L.A.B. my multimeter has a " continuity " setting, emitting a " tone " at continuity.

Last edited by limeyrider; 05/16/18 11:13 pm.
Re: what's going on ...or not. [Re: limeyrider] #735605
05/17/18 12:49 am
05/17/18 12:49 am
Joined: Jan 2008
Posts: 330
Concord Township, Ohio
57nortonmodel77 Offline
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Posts: 330
Concord Township, Ohio
Hi Limey RIder, sending a PM your way smile


Magneto & Dynamo restorations & supplies

My Bikes
1948 Norton 500T Trials bike
1950 Norton Model 7
1952 Norton ES2
1957 Norton Model 77
1960 Norton Nomad 600cc Desert sled
1961 Norton ES2 (slimline)
1964 Norton Atlas Scrambler
1972 Bultaco Alpina
Re: what's going on ...or not. [Re: limeyrider] #735644
05/17/18 11:27 am
05/17/18 11:27 am
Joined: Jun 2002
Posts: 10,293
Scotland
S
Stuart Offline
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Stuart  Offline
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S

Joined: Jun 2002
Posts: 10,293
Scotland
Hi,

Originally Posted by limeyrider
1966 650 SS
The bulb holders do not have ground / earth wires, the instruments are mounted using two studs, the studs have a small rubber ring sandwiched between the back of the instrument case and the mounting plate which bridges the forks. The rubber rings were original pieces ... or so I'm told ....I have not been able to find them in parts manual though ??

Removing the rubber rings will remove any vibration dampening to the instruments, perhaps adding a ground / earth wire is the solution ?

It is.

Slightly later Triumph twins mount the speedo. (and tacho.) on a plate insulated from the top yoke by Metalastik (rubber sandwich) bushes. Speedo. (and tacho.) bulb holders have only a supply wire, "ground/earth" is through the mounting so it's interrupted by the bushes. Solution is a wire between either speedo. (or tacho.) itself or their mounting to one of the main "ground/earth" wires inside the headlamp shell.

Hth.

Regards,

Re: what's going on ...or not. [Re: Stuart] #735698
05/17/18 8:01 pm
05/17/18 8:01 pm
Joined: Aug 2009
Posts: 1,116
gastonia .. NC
L
limeyrider Offline OP
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limeyrider  Offline OP
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L

Joined: Aug 2009
Posts: 1,116
gastonia .. NC
An earth / ground wire from the speedo mounting stud into the back of the headlamp shell cured the problem, both instruments now have " lights " ... 2 watt bulbs !!.


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