Technical Help me wire this old tach!

I recently bought this old tach but can't find any info on it, unknown whether it still works. I assume it's an actual Mooneyes product but I suppose someone could have stuck a tiny sticker in there. Everything appears to be there, no cut or broken wires inside, all the screws are still in place. The wires are black, white, gray, and purple, the black wire has a piece of tape on it with GR written on it so I'm assuming that's ground. The "cup" is heavy cast metal, the whole assembly is quite heavy, right at 2lbs 1oz. I figured the white wire would be power for the light so I touched the white wire to the positive side of a battery and the black to negative, no light came on but the needle moved about a millimeter each time I made contact. I didn't check the bulb so it could be burnt out, if it's even in there. Anyway, if anyone has an idea how to wire this thing I'd really appreciate the help, I'd like to be able to use it if it works.

 

Looking at the circuit board photo... Black wire is ground. Gray wire is the light circuit. White wire is trigger wire to coil. Violet wire is + battery connection.

 

Thank you! I'll give that a try. If the white wire is the trigger, it would go to the negative side of the coil, correct?

 

Yes... That is correct. Hopefully you didn't damage the tach when you put the trigger wire on the positive battery terminal. I know guys that have done that before and the tach didn't work afterwards. Good luck.

 

Hopefully not. that would suck. I'll have to wait til Friday to wire it up and try it, fingers crossed it works.
On the bright side, the light works!

 

Well... At least you'll see it at night!

 

Is that a real Moon tach? Is the logo printed on or is that a sticker? Cool tach either way, I hope you get it working.

 

Thanks. Don't know of it's real mooneyes or not. Might be a sticker but it seems like it would have been a lot of trouble for someone to go through to take it apart and put it back together just to put a little sticker inside.

 

I agree...it might be an early tach Moon offered. Looks like an old Keltronics tach I have. Probably late 50s to early 60s would be my guess. I wouldn't call it Mooneyes. That's what the company has been called since Chico Kodama took it over in the late 80s. This tach is clearly old.