hello
A couple years ago I converted my car to digital cluster (from a donor car). I fitted the old analogue speedo/mileage reading into a small windowed box with the relevant electronics and wired it into the trunk. It's worked fine til now but has suddenly stopped working.

It's so long ago since I wired it all up I can't remember one detail about how it's powered.

To make the speedo work independently, I've a speed sensor connection, earth and positive connection wired into the trunk.

I've volt-tested the speedo (in the trunk) and the + connection only reads 2 volts.

I'm guessing this is where my problem lies as I'm 95% sure this should be 12 volts, but don't want to mess up the speedo if I'm wrong (but can't think where 2 volts could possibly come from). I'm assuming this is due to a bad connection at source.

If someone knows 100% that it should be 12 v that would be cool.

Many thanks
Andrew

 

If its a two wire its not really powered. It creates a voltage when it turns. So you dont need to hook it up to a power source.

 

thanks for your reply, much appreciated.

I was always under the impression the speedo ran off three wires... (there are 3 connections on the back of it if it's removed from the main cluster). One is definately earth, one speed sensor and I thought the 3rd was 12volt + (though mine's reading 2 volt for some reason). I thought the speed sensor sent the speed signal to the speedo and the 12 volt + provided the power to the electronics to power it (as I would have guessed this would need to remain constant, to power the servo on demand?) Maybe I'm wrong... (the + isn't for illumination as that's separate)
I'm not sure now!! I would test it out but in case I'm wrong on the voltage I don't want to blow the speedo.

 

I've just been testing it again with voltmeter and it's a bad earth causing the 3rd wire to read 2 volts. It is in fact 12 volts...

 

The three wire you describe is a little different than the two wire i mentioned earlier. One wire is a power, one a ground, and the third is signal wire. The signal is usually in the middle. Im glad you were able to find the problem with your sensor.