Glad to hear you got it working. The only funky thing I can remember about the LC-2, is that it has a combined signal and power ground. Ya don't want to ground it to signal ground on the MS. Everyone is pretty adamant about grounding it to the engine along with the main harness ground. I don't know why or if that would bork up your RPM signal though.

if you wire through the MS, pull power directly from 1B to the DB15-- dont use a 12v hole -- it can't supply the amperage needed and will cause issues.

They had it wired directly to the 12v and Ground on the main board. i changed it to 1B and 4A on the BOB.