Hi,

I changed out the alternator on my 2003 R53. The new alternator only had one nut for holding on the negative cable. The previous alternator had two nuts. I took the one nut off of the old alternator and used that to hold on the negative terminal. When I tried start it up after connecting the battery it acted like there the battery was totally dead, but I know it isn't. I suspect that the negative lead to the alternator was grounding out somehow. I was wondering if I should try to use just one nut and see if I can get that cable in deeper in the plastic cup or trying to rotate the cable ninety degrees.

 

The heavy gauge wire to the alternator is battery positive and hot at all times unless you disconnect the battery negative cable. The only thing the positive connection at the alternator needs is a good electrical connection and I usually only see alternators with the 1 nut to secure the cable to the alternator. I would remove both nuts from the alternator post and attach the cable to the post and secure it with 1 nut. Snug is fine. The alternator grounds itself to the engine block which itself is grounded by the engine strap to the body.

Also don't forget that other connector to the alternator.

 

I refitted the alternator to the engine and reconnected the positive wire to the alternator using just the one nut that was provided. It seems like the positive wire was too tight a fit in the plastic cup, because I felt a pop that I think might have been the plastic cup cracking, but the wire seemed to have a good secure connection and doesn't seem to be touching the engine any where. I then reconnected the ground strap to the battery. It seemed like there was more sparking than normal when I did this. I turned the ignition to the ACC position. The digital voltmeter I had plugged into the cigarette lighter looked pretty normal 12.3 Volts or so, the car hasn't been driven in a month or two. I then turned the ignition to on and everything still looked okay. I then turned it back to ACC and the it was like the power was killed.

My previous alternator tested as having an "bad diode" at Advance Auto, the reason I was having it tested was the car would act like the battery was totally dead when it tested as okay. It kind of seemed like there was a serious intermittent parasitic drain on the battery. Which totally seems consistent with the bad diode. I'm wondering if my new alternator has a similar problem or there's some other intermittent short to ground on the cars wiring harness.

I've used my continuity tester on my multimeter to test for continuity between the postive terminal on the alternator and the body of the alternator. What I see is that the continuity tester will beep for a few seconds when I touch the postive terminal with the probe on my tester and then go out. If I switch the terminals on the meter so I have positive connected to ground and negative connected to the terminal it will beep for a few seconds and then go out. If I switch leads on the meter it will beep for a few seconds and go out. I'm wondering if this is normal.

I just pulled the alternator off the car and it doesn't do this. I don't hear a beep when I check continuity between the positive post and ground, so it must be somewhere else.