I have the SC400, there are (+) and (-) illumination wires that the OEM factory head unit has. The aftermarket has just one lead. Please help how am i going to wire this to make it works. Are there any other leads can be tap it?

 

Break out the test light and find the signal at the head light switch on the steering column.
Aftermarket h/u's only need a positive lead.

 

Thanks much Vin 78