+1
It would help to know the type of original installation you're working with.
If it's a base line unit, then I would start looking at the power wiring first, making sure that the usual permanent and switched 12 volt feed are present and working.
If it's the HK Hi-line set-up .... well, after looking at the wiring diagrams then I would advise you to seek professional advice from a vehicle ICE specialist.