First, check that the battery warning light turns on when you turn on the ignition switch.
Check the voltages on the wires where they plug into the generator. The yellow one must have 12 volts all the time. If it doesn't, look for a blown 15 amp fuse. The green / red wire should have around 2 volts with the ignition switch turned on and the engine not running, (that's what turns the dash light on), and over 12 volts when the engine is running, (that's what turns the dash light off). If you find 0 volts on that wire, there's a problem in that wire. If the dash light is on, that wire is grounded. If the dash light never turns on, that wire is open, typically in a connector pin that is corroded.
If those voltages are good, measure the voltage on the white / black wire on the back of the generator when the engine is running. If the unit is working, there will near 6 volts on it. Also measure the voltage on the large output wire. It should have full battery voltage all the time when the engine is not running, and must have between 13.75 and 14.75 volts when the engine is running.
Also measure battery voltage while the engine is running. If it is between 13.75 and 14.75 volts, the charging system is working and something is likely draining the battery while the car is sitting.
Thursday, February 3rd, 2011 AT 8:26 PM