Need help with Daytona tach and shift light!!

I have a Daytona analog tach to install on my GS500. It was given to me without instructions and I need some help getting this right.

The tach has 4 wires: red, black, white, and yellow. I hooked the red to the battery +, the black to the battery -, the yellow to the coil and then left the white wire alone. I fired the bike up and fiddled with the DIP switches until the tach read something believable. I took my tach from my stret bike and hooked it up to the race bike to see if the Daytona read the same as the stock tach. Up to 4,000 they're pretty much spot on. As the revs go up, the readings diverge. I don't have much faith in the mechanical tach but since I'm not sure if I installed the Daytona right, I don't which to believe.

I also have a Daytona shift light. This device has 3 wires: red, black, and black/white. I wired the red to the battery +, the black to battery - but when I put the black/white on the coil wire (same one as the tach pickup), that cylinder quit firing. I switched to the other side of the coil and the light didn't respond at all even after I fiddled with the two adjustments.

Anyone have installation instructions for these things that can be copied and sent to me? Anyone install either of these? If so, can you 'splain how it gets wired up?

Thanks.