Electric Tach and signals working intermittently

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Jason OBrien
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Electric Tach and signals working intermittently

#1 Post by Jason OBrien »

Hi all,

I've had an intermittent problem with my car for a bit that has stumped me. The car is a 64SC coupe with electric tach that I restored a few years back.
My electric tach and signal lights occassionally stop working for no rhyme nor reason that I can tell. I can be driving along and take a look down at the guages and they are not working. They often come back on line by themself without me doing anything to solve the problem. Other times they don't come back until some time latter. I can't see any particular pattern to when this occurs (eg rev the engine, turn the signal indicator on). I'm stumped.
I've replaced the electronic flasher with a unit from Zim's and this hasn't solved the problem. I have a copy of Joe Leoni's book but must admit to not being an electrical guru. Any thoughts?

JO

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Doug McDonnell
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Re: Electric Tach and signals working intermittently

#2 Post by Doug McDonnell »

Poor ground.
1965 356C 2000 BMW 740i Sport 1967 Honda CL77 There is never enough time to do it right, but always enough time to do it over.

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John Weyand
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Re: Electric Tach and signals working intermittently

#3 Post by John Weyand »

When an electrical problem crops up and affects more that one element the most likely culprit is a faulty ground. There should be a brown wire that jumps from instrument to instrument with a slide on (spade) connector. Check to see that the ground wire is firmly connected to all the gauges and switches as appropriate in the dash. Then be sure that the jumper wire is firmly and cleanly connected. I don't have a diagram handy but I think there is a connection to the body behind the dash. I'll go look at the diagram in my shop later.
John W
'64 "C" coupe

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Doug McDonnell
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Re: Electric Tach and signals working intermittently

#4 Post by Doug McDonnell »

On a C ground will usually be at or near wiper. But if only one instrument affected it will be the connection at the instrument.
1965 356C 2000 BMW 740i Sport 1967 Honda CL77 There is never enough time to do it right, but always enough time to do it over.

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Greg Bryan
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Re: Electric Tach and signals working intermittently

#5 Post by Greg Bryan »

Has your car been converted to 12V? If so there may be a 12v-6v converter that is acting up.
Just a SWAG ... Depending on how it is wired, it could affect the tach and the other instruments.
And yes, check grounds. The main ground point for the under-dash ground wires is on one of the windshield wiper frame mounting bolts.
Another common point between the electric tach and the turn signals is that they derive their power from the #15 terminal on the ignition switch (powered when the key is on only). There are three wires in the bullet receptacles on the ignition switch #15 terminals, one goes to the instrument power (blue/yellow), one goes to the ignition coil (black/white) and a black wire goes to power Fuse #1 - the tach's power source is spliced to this black wire, too, if the car came from the factory with an electric tach which started in the late '64 model year. Check that the black wire is nice and snug where it attaches to the ignition switch. In addition, there are three circuits on the #1 fuse that are powered through the black wire, the back up lights, the brake lights and your problematic turn signal flasher. If you are also having problems with the back-up light and brake lights, that is further evidence of the black wire not having a good connection.
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Jason OBrien
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Re: Electric Tach and signals working intermittently

#6 Post by Jason OBrien »

You guys are awesome! Thanks for the help. The same thing happened earlier today and I looked at the black wire which seemed to be a bit loose. I jiggled it to make a better contact and the tach immediately started workign again. I think the cause is that the bullet from the Y n Z harness might just be a bit loose in the female receptacle on the ignition switch.

Best regards,

JO

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Doug McDonnell
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Re: Electric Tach and signals working intermittently

#7 Post by Doug McDonnell »

Thanks for the followup on your problem. Now someone in the future who searches can know for sure of one possible cause.
1965 356C 2000 BMW 740i Sport 1967 Honda CL77 There is never enough time to do it right, but always enough time to do it over.

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