I've looked at countless other posts and can't seem to find anything like my problem so I'll give it a go posting myself.

My car is a manual, 2000 targa top, with just over 100k kilometers, It's had small electrical issues that I haven't thought much about for most of my ownership of the car which I have had for about a year and a half now. For starters, my voltage readout jumps all over the place, it goes from mid 14s to high 16s and back down all in a matter of seconds and the charge system fault pops up and goes away seemingly random while driving. The fault can stay on the DIC for 20 seconds, go away for 2 seconds then come back for another 5 seconds and continue with this randomness my entire drive. The electronics on the interior of the car (radio and climate control displays) seem to pulse in their brightness, same thing happens with the headlights when I have them on. And the most annoying part is that sometimes my turn signals stop working, I'll hit the stock up or down and nothings happens, no indicator in the dash and no lights on the outside, it comes back eventually but it could be there one second and dead the next, sometimes it comes back for one "tick" of the indicator then dies again.

I've dealt with these issues for a while but it's seemed to get worse with time and recently I came back from a track day and now it's the worst it's been. My voltage was sitting at mid 11s while driving for a while until it went back to jumping around from 14-16v and at one point the display for my climate controls wasn't showing anything.

My best guess would be an alternator problem because I know these cars are very particular with the alternators they use and mine appears to have a new one, but I've read it could also be a faulty ignition switch or a bad ground.

Any help would be appreciated.

Thanks.

 

I had a similar issue in the past with another C5 I owned. Sounds like a voltage regulator issue inside your alternator.
I changed mine out and the problem was gone. It's an easy DYI. I was not getting the voltage fluctuation, but definitely the flicker in the interior lights and such.

 

Yep, as I was reading the post I was thinking the same thing. Swap the alternator/voltage regulator and I bet the problems will be gone. BTW... an easy check would e to take your car to Auto Zone (or others) and they will put your car on their meter. This will tell you the condition of the alternator, battery and starter. Easy Peasy.

 

Battery, alternator (changed), and especially, BAD GROUNDS, are by far the C5s electronics worst problem.

 

My alternator looks relatively new, would this be a case of the wrong alternator being installed? Do you have a model/part number of the alternator you put in the car? I just don't want to go buy a new alternator for the same or new issues to pop up because I have the wrong one again. Thanks for the help.

 

I went to Rock Auto. You should check it out.
They have real Valeo alternators.
Mine is a 2000 auto trans. The alt pulley with or without the clutch is fine.
The one I bought had no clutch, neither did my stock one. Kind of nebulous for the 2000.
Anyway, works perfect, no codes.
The voltage you see will wander around because the pcm controls it. But should never be 16, or 11.5.

Check them out

 

That was on a previous C5 I had. I remember just walking into an Advance Auto Parts and giving them the year and model of the car and they matched it just fine.

 

Thanks! I just ordered a Valeo one from rock auto, it should be here in a few days and hopefully it fixes my problems.

 

When you change your alternator, definitely disconnect your battery before you mess with any wiring. First, don’t risk shorting some wires. I have read stories of sensitive things shorting out. Second, go ahead and pull your battery to clean the ground point under the battery. That one is easy to get at since you are disconnecting the battery anyway. Clean that ground and also clean your battery connections.

 

There is one potential problem with checking an alternator off the car. If it checks bad.at the auto parts store, it's probably bad. BUT, even if it checks good, it could still be bad. Here's why; I don't know how many C5 owners have opened their hood after a 20-30 mile trip, but if you do, expect a LOT of heat to come billowing out. My point is, the alternator is pretty hot in those conditions. Heat and electricity get along as well as Biden and Trump, maybe worse!! When your room temp alternator is checked at Bimbo Jimbo's auto parts, it may check out fine. Heat it to 150°-200° in the car's actual running conditions, and it may NOT check out fine!! Best way to check is with a DVM/DMM. Start your car, and drive it 10-15 miles to accumulate heat under the hood. Stop car, open hood, turn the meter on, and set it to DCV (D.C. Volts). Then, touch the red probe to the positive post at the back of the alternator, the one with a red cable fastened to it. Then touch the black probe to any good ground. You should see at least 13.5-13.8 volts, and it shouldn't be jumping all over constantly to 15, then 12, then 14, then 16, etc. If it's steady, and at least 13.5 volts, you should be good. If it's steady, and reads 16 volts, or more, or 11 volts or less, your regulator is junk. Many guys here who know more about it than I do suggest replacing diodes in your old alternator, rather than buying a new, different alternator. FWIW, I have a 2000 vert, original alternator, 130,000 miles. My alternator has the clutch........