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Wiring Of Tacho Wires To 3-gauge 1275gt Instruments


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#1 The-Wizard

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Posted 12 February 2011 - 11:39 AM

Model: Clubman 1275GT
Year: 1970
Description of problem: I'm wondering what wires go to which connection

i'm in the process of changing wiring loom on my car, and i'm converting from 2-gauge to 3-gauge 1275GT instruments.
but i'm wondering which wires that should be connected to what terminal on the tacho.
back of the tacho looks like this:
Posted Image

i've got three wires from the harness that i have "spare" after wiring the main gauge connector
1. Green powered from ignition
2. white from ignition switch
3. White/green that goes to + on coil

I'm using this schematics for the wiring
Posted Image

i found this text in a thread here, but none of the looks like my tacho.


RVI 1275GT Tacho
Male spade connector - 12V IGN Source (white wire)
Small Screw below spade connector - Earth (usually via screw into PCB)
Female bullet socket (next to screw) - Connection to coil +ve (white/green wire)
Male bullet (above female) - 12V IGN Source (white wire)
Posted Image

RVC 1275GT Tacho
Male spade connector - 12V IGN Source (white wire)
Small screw nearest male bullet connector (top right in photo) - Earth (usually via screw into PCB)
Male bullet - Connection to coil -ve terminal (usually white/black wire)
Posted Image

For future reference - ignore the wire colour shown in the photo above as it is incorrect!!!!


does anyone know what signal that goes to the spade and bullet connector? i'm wondering if the instruments i've got is from a 1976+ car. and that it needs signal from - on coil?

#2 Dan

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Posted 12 February 2011 - 11:53 AM

Your wiring is not compatible with that type of tacho. Your tacho is not a 1275GT instrument it's much later (1988 at least), and although it doesn't look identical it is the same format as the second one you found a photo of. It's an RVC type. Connect the white directly to the white/green to run your ignition system (make sure this is a reliable connection), then run a new cable (preferably in white/black) from the coil negative LT circuit to the bullet connector on the tacho. The green can still power the tacho, through the blade connector.

#3 The-Wizard

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Posted 12 February 2011 - 12:17 PM

Your wiring is not compatible with that type of tacho. Your tacho is not a 1275GT instrument it's much later (1988 at least), and although it doesn't look identical it is the same format as the second one you found a photo of. It's an RVC type. Connect the white directly to the white/green to run your ignition system (make sure this is a reliable connection), then run a new cable (preferably in white/black) from the coil negative LT circuit to the bullet connector on the tacho. The green can still power the tacho, through the blade connector.

Thanks alot for the clarification!
should i be concernd about the multiconnector pinout? i've wired it like it was with the original wiring with 2-gauge clubman 1000 instruments.
the wire harness from mini spares came without the connector so i got a connector from a another car, took out the wires and configured it like my original 2-gauge dash.
do you know of a site that got pinout for the instrument i've got?

#4 Dan

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Posted 12 February 2011 - 12:50 PM

Sorry no, you'll have to trace the PCB unless someone else knows of one. All post '76 multi connectors are the same but I'm not certain about the earlier ones. Given that the tacho is so different they can't be identical, although there is at least one unused pin in the later plug so the rest may be a match.




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