tach hook up

[Fired Up]

Picked up an inexpensive tach to hook up in my motorhome. 4 wire hook up: red,ign source; black, grnd;green,neg coil terminal;white, dash light source. Doesn't work. The tach light works, but no rpm's. Any chance the coil lead connection might be the pos. instead of the neg.? No instructions came with this tach.

[Fiat48]

Nope. What kind of motor home, year etc? MSD box on motorhome?

[Fired Up]

Hi Fiat,
1990 34' Southwind on a Ford chassis. 460 EFI. Standard Ford electronic ignition. No fancy ignition systems. Stock motor...etc.

[Fiat48]

Everything I can find even on electronic systems shows green to neg side of the coil.
Here's some generic instructions:http://www.sunpro.com/tachman.pdf
Can't see why you'd hurt anything trying the positive side. It'll either work or not.

[Fired Up]

Thanks Fiat,
Don't know why I didn't find that site when I looked for instructions earlier. It gives me a few options to try.