Speed and tachometer

Alright guys, I’ve got a thinker. I’m installing an aftermarket digital speedometer and tach on my 85 Honda shadow. Everything seems to be wired up correctly and working fine. Turn the key to the on position I have all my lights working correctly (high beam, blinkers, etc.). However, when I actually turn it over and get the bike running, all on the lights illuminate and it no longer functions correctly. Anyone run into a similar issue!?