On a 2003 fat boy, which color wire to the coil is negative, to wire a tach signal to?

Faulty crank position sensor

The green wire from the tach goes to the negative side of the coil or if its an HEI distributor it will connect to the left of the hot wire going. to the distributor.

It sounds like the RS82 is not getting a proper tach signal. If you are using tachless mode, the 12 volt constants may not be providing the desired signal. Recheck your connections to ensure that they are solid. The high amperage wires should be soldered. You will need to connect the tach wire if the connections are good. The tach wire can be connected to the negative side of the ignition coil's blue/brown wire or the blue/green wire at the PCM or you can use any one of the uncommon colored wire at a fuel injector.

I am sorry but fixya has no wiring diagrams.

There are two wires that connect to the coil, one is battery voltage, you connect to the other. Some meters need an additional part to 1/2 the signal, as stock fires all coils at all spark requests, thereby doubling the reading.

It should be black,but look on the coil,and it will have a negative sign in the coil next to the terminal like this - Now this terminal,will go to the ignition.

Tachometer Wire Negative Wire (-): Any Wire That Is Note Red/Light Green. The diesel tach wire is a green/white wire, located in a 5-pin harness held up with tape behind the parking brake release.
Tachometer Wire Negative Wire Location: At Igniton Coils

According to wiring diagrams online... good luck with this.
KEn

wow how did that happen , they should have, well you can by a after market kit that comes with the wiring harness for frt and rear. if it was me thats what i would do . that way you can install some costom lights be ready through they are not cheap kdc744

I show Pink - coil to Ignition module and white/black - coil to harness