First of all, never disconnect the battery while the engine is running. That was a trick done many years ago by mechanics who didn't understand how these simple systems work, but on today's cars it's a real good way to destroy numerous computers in a few seconds. The battery is the key component in helping the voltage regulator maintain a safe system voltage. You have all the information you need with the voltage reading. The battery voltage must be 13.75 to 14.75 volts with the engine running. 12.22 means the charging system is dead and the battery is good but nearly run dead.
Also, the red warning light means the battery is not being recharged while driving, not that the battery is bad. It's telling you there's a charging system problem. Start by measuring the voltages on all of the wires on the generator with the engine running. Holler back with those wire colors and voltages.
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Tuesday, June 12th, 2012 AT 3:05 AM