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Had a situation where the battery was not reading 13.8v while the car was running(was showing around 12.1v). Battery was draining and not being charged by the alternator.<p>Replaced the alternator this morning on my 94 GS V6 (what a pain to get at it). Hooked everything back up and the battery is *STILL* only showing 12v when the engine is running. <p>What in gods name could be causing the alternator to *not* be charging the battery/powering the engine? The belt is fine, turning properly. Any ideas?<p>Update: Measuring Alternator voltage directly yields a proper 13.8v. Somewhere between the alternator and the battery is an open circuit preventing the battery from being connected in parallel with the alternator(and having the same voltage). No *freaking* idea where this fault may be.<p>Update 2: After checking the wiring diagram the alternator is hooked up to the 30A fuel inj fuse and the 100A main fuse in the main fusebox. Measured voltage at the 100A fuse is 13.8V. Resistance between the 100A fuse and the +ve terminal of the battery is zero. All fuses are ok, none blown. Im really running out of ideas now. What could cause the battery, which IS hooked up to the 13.8V alternator output to show a 12v output at its +ve terminal?!?!<p>[ April 30, 2003: Message edited by: Atlas ]</p>

How long did you run the car for? It takes about 20 min to 1/2 to recharge a battery once its been drained.

You've checked the +ve wiring, but have you checked the grounds? A high resistance between battery -ve and the ground is one possibility, but also check between alternator -ve and ground.