Stuborn Electrical Problem '02 Boxster - 986 Forum - The Community for Porsche Boxster & Cayman Owners

Steve Tinker · 12-08-2010, 02:10 PM

On the face of it, it certainly looks like an alternator problem - barely 13 volts with no load seems low.
I wonder what the v reading is if you leave the engine running, switch on all the lights, fans, A/C etc and then read the battery voltage again. I wouldn't be surprised if its even lower - maybe even drawing current from the battery ....

PB2002 · 12-09-2010, 08:34 AM

Steve:

You are correct. When you turn on the lights, A/C radio etc. with the engine running the voltage drops into the 12.6 - 12.8 range. I am going to replace the alternator again under warranty and see if this solves the problem.

By any chance do you happen to know what function / system the plug on the alternator serves? There are three wires on the alternator. The thick cable and red wire (with the eye connector) that is bolted to the back. The other wire (blue) is terminated with the black mercedes benz connector which plugs into the back of the alternator. It travels back into a wiring harness. Do you know what this wire supports or what its function is related to the alternator?

PB

Steve Tinker · 12-09-2010, 04:47 PM

I think the wires that eminate from the connector are for the charge warning light and field energising circuit. They will be control / indicator circuits though.
I could be wrong - its been known before....

One thing I did forget to mention is that the battery must be fully charged when you check the alternator output voltages - a half charged battery can give all sorts of strange numbers. Charge for at least 12 hours and test as mentioned.....

PB2002 · 12-09-2010, 08:46 PM

I thought the connector wire might be the warning light. Just wanted to get your thoughts on whether is was sending some type of instructions to the alternator, but I suppose all of the "brains" that control output voltage are in the alternator. I will recharge the battery again and do my tests. I am taking the car to the dealer next week to have them test the ignition switch again. As one of our earlier members suggested, the switch they replaced in June might have failed. Stay tuned....

PB2002 · 12-27-2010, 01:17 PM

Steve:

Just wanted to close the loop on this thread...I took the car to the dealer and they tested the ignition switch and confirmed it was not the problem. They then wanted to charge me $200 to begin testing the wiring to find where the problem was coming from. I decided to give it a shot myself. When I got home, the new "replacement" alternator had arrrived so I swapped out the one I put in a week ago and Voila! The voltage test put it at 14.2 volts, just where you thought it should be...

However, the lights continued to flicker and the stereo still cut in and out. I then removed the Positive (not negative) lead from the battery to the connection in the firewall and found a small amount of corrosion on the firewall connection. I cleaned both ends and reconnected and the flickering went away!!! I was shocked and surprised that such a small amount of oxidation could have that much of an impact. Nevertheless, the problem is fixed.

Thanks to everybody who provided input on this issue, it greatly helped.

PB2002.