I have a 99 *.e. with 122,00 on the clock. My issue is for about 3 minutes after starting the voltage stays up around 14v, then it starts to fluctuate between 11.9 and 14v constantly with or without a load. When I put the voltmeter on the batt it showed the exact same thing..voltage cycling between 11 and 14v. I have replaced the alt with another delco 140 amp and I have also replaced the battery at the same time. I have cleaned every possible connection there is between the battery and the alt. and body grounds I am totally stumped. The only thing left is the P.C.M. is this a common problem on the 99'*...please help
p.*. where do you get the light up bonneville in the back?????

Welcome to BC. It sounds as if there may be a cycling load, a significant load at that. It may be a tedious process to isolate this. Try to get a clamp on ammeter on the positive side of the battery to monitor current if possible. You will have to selectively remove fuses to isolate.

I like Marks line of thought and would like to add to it.

When removing the battery cables and cleaning, did you find much corrosion? If so...pull the cables off the battery again and remove the plastic boots. Look at the crimped area of the cable specifically. Much corrosion? It'* possible that the issue could lie in the cable itself.

If your voltage was high, then dropped and stayed low.. that would be expected..... the fluctuation is interesting. Have you swapped the alternator again or brought it in for testing to ensure the regulator is not bad?

On the tail light. You don't buy it.. you make it

http://www.bonnevilleclub.com/forum/...ight=9699+tail

The only time I experienced something like that, it was a bad regulator in the alternator. It would seem strange that two would have the same problem. Check the wiring to the alternator, also.

its the third altenator the other 2 were replaced under warranty same problem exists tho.. as far as the cables go I took off the boots and made sure that everything was clean. I really dont think it is a cycling load tho due to the fact that the amp load never changes..

I just recently went through a similar situation with my 99. My volts were fluctuating bad on a recent trip to southern KY. I finally ended up pulling over to further investigate and tracked it down to the jet ski trailer that I was towing. The socket was shorting out--the positive and neutral would arc against one another and make my volts drop. For the purposes of my fix, I just removed the bulb and bent the prongs in the socket so they couldn't touch.

Your fix might be along the same lines, but within the car. Follow Mark'* advice and trace down the circuit giving you headaches. From there, investigate the sockets in that circuit.

this happens with no load other than the p.c.m. and fuel pump...I checked voltage at the pump today and it coinsides with the cycle of the altenator...I briefly pulled the fuse for the pump and the cycling didnt change...tho I could only watch it for about 10 seconds before it stalled

What indication do you have that there is no load on the electrical system? There isn't an ammeter on your Instrument Cluster that I know of. Anyway, voltage fluctuation coincides with electrical loading. If you drop a large load on the system such as the rear window defogger, voltage will drop initially, then the voltage regulator will boost voltage back up. When unloading by turning defogger off the voltage regulator will regulate down. You can have voltage fluctuations with out load changes I admit through some fault in the alternator/voltage regulator. Generator field current is switched (pulse width signal) by the voltage regulator to regulate output. Either there is bad cabling (corrosion underneath cable jacket or (+) & (-) terminal lugs) as pointed out by Boosty, or something is adversely affecting the voltage regulator.

Have any water leaks...maybe a questionable ground in the busses by the front doors under the carpeting?

Have you tried output right at the alternator? Also maybe check the ground of the alternator. The housing should be grounded with very little voltage drop to the battery negative terminal.