If your running voltage is below 13.5volts with your lights on then you have either a bad alternator, bad alternator fuse (located in engine compartment) or a shorted out battery. Your electrical system will not work properly unless the running voltage problem is corrected and testing wiring is useless if the battery isn't fully charged working with a good alternator. There are more than one GEM module on these vehicles so it probably is not those. | 
