Car Stereos: fitting a stereo in a gmc safari, using a digital multimeter, sony head unit

Question
hello ive recently bought a gmc safari and im trying to install a sony head unit but i cant get it to work i think the gmc's head unit the oringal one runs at 15v were as my sony is a uk 12v how do i get around this thankyou

Answer
Hi James,

Sorry about the delay in answering this question; I realize you may have your problem figured out already.

I've never run into a vehicle that's made to operate on a 15 volt system; just about any after-market car audio component is designed to work in a voltage range between 11 and 15 volts.  This is because most vehicle electrical systems rest at 12.6 volts with the engine off (if the battery is fully charged) but they produce over 14 volts when the engine is running and the alternator operating.  

Some newer GM vehicles have factory radios that operate through the vehicle's data bus system, rather than a key-switched power wire.  If there's no key-switched wire in the factory radio harness, that might be why you're not getting the head unit to turn on.  The solution is to use a special adapter module that works with the data bus system and generates a switched power voltage, or connect the head unit's power wiring to a switched power source somewhere else in the vehicle.

You can troubleshoot any power problem using a digital multimeter set for DC volts.  Connect the meter's black probe to the head unit's black ground wire; use the red probe to test the voltage on the yellow constant power wire, and the red switched power wire, with the vehicle's key on.  Both wires should show a voltage over 12 volts.  If you find a wire that doesn't test with voltage, then you can start trying to figure out why--the vehicle's fuse box is usually a good place to start.

Hope this helps!

Brian