engine and drivetrain My 02 is dead. No power!

[Supergeek]

Sorry for the longish post. I'll try to explain everything that happened and everything I did.

1. Got off of work last night and started my 02. Car started right up but I did notice that the interior lights and headlights were dimmer than usual. Drove home (1 mile) and all the lights were significantly dimmer. I turned the car off, and it didn't turn back on. Battery had power but not enough to crank the engine.

2. I first suspected the 55 amp alternator that I picked up from a junked 320i at the junkyard. It worked well for a couple of months but I figured it had died. Fortunatly I had my tools and my old working 35 amp alternator in our garage so I swapped them. The L alternator charging light never turned on, though.

3. After swapping alternators, I grabbed the battery from my girls Taurus and used jumper cables to jump start my 02. I checked all the connections and cranked the engine. Car started up right away and all seemed well. After about a minute of running the car, I disconnected the jumper cable from the negative battery post and clamped it to the chassis. The car immediately died. I tried to turn the car back on but I had no power at all. No lights worked. Gauge cluster warning and the brake light didn't work. The only lights that worked were the fog lights that draw power directly from the battery, so the battery had some power left.

4. Stumped, I checked to see if I installed the alternator wiring correctly. It was then I realized that I had totally forgot to plug in the voltage regulator which I had removed when I installed the 55 amp alternator! Damn! I reinstalled the VR. I checked the relays, they all looked good. I checked the fuses. The only blown fuse was the number 11 fuse, which is for the highbeams? I replaced it. Still no power at all. I checked my wiring under the hood and under the dash and didn't find and burnt or unplugged wires. I finally gave up at around 1:30am when my girl told me to get some sleep. So we pushed the car into the garage and called it a night.

What else can I check? Can it be the ignition switch? I have the OG BMW blue repair manual and the Haynes one too. Unfortunately I didn't have them with me. Any info would be GREATLY appreciated. Thanks. Have a great day.

[Kidasters]

Have you checked whether or not your battery is toast? It may not take a charge now....

[PeterVarga]

Yeah...recheck the battery. It may have enough to let the lamps lit but not enough for the start sequence. On mine, a measurement of 12.41 vdc is enough for starting but 12.34 isn't. Get out the voltmeter and test your battery.

[Napes]

I, too, think the battery is the culprit. When batteries discharge, the deposits that have built up on the plates sluff off and fall to the bottom of the case. If they build up enough to touch the bottom of the plates you will not be able to hold a charge. I'd run the battery down to your local AutoZone or Checker (or whatever auto parts store in your area does this) and have them fully charge the battery, then run a load test on it. It'll take 'em an hour, but you could easily spend more time than that checking things. Start w/ the easiest things to check 1st.

Bob Napier