Left a party around ten and about five minutes later noticed the headlights dimming and then brightening and dimming again. AC was on and I noticed the amp gauge, which always reads dead center at 13, was showing discharge (around 11). I got on I-95 heading south and the amp gauge finally returned to center position but the dimming and brightening headlight issue continued. Anybody got a clue as to what's going on?

 

Could be alternator, corroded cables getting an intermittent connection, but i'd diagnose it some more by seeing if the pattern repeats itself next time you drive...with and w/o headlights, then repost.

 

I had a similar issue a few years back. But along with the dimming I had a recurring starting issue. Usually when it was hot I would drive to a destination, park and when trying to leave I would get nothing. After a cooling off period it would start fine run fine. The dealership mechanic knew exactly what was wrong when I described this issue. He had seen numerious corrosion problems with the positive cable. that would cause shorts and the like. We ended up replacing both positive and negative cables on the car and all has been good since. 99-XK8 70K Coupe. As I recall the repair was in the neighborhood of 400.00-500.00, Dealer.

 

Thanks guys, I'll keep an eye on it and see if the problem repeats. I'll also check the connections at the battery. Hey, when things are running right, where is the needle on the amp gauge supposed to be, straight up at 13?

 

http://www.bcae1.com/charging.htm




Charging System Basics: The electrical system in an automobile is said to be a 12 volt system, but this is slightly misleading. The charging system in most cars will generally produce a voltage between 13.5 and 14.4 volts while the engine is running. It has to generate more voltage than the battery's rated voltage to overcome the internal resistance of the battery. This may seem strange, but the current needed to recharge the battery would not flow at all if the charging system's output voltage was the same as the battery voltage. A greater difference of potential (voltage) between the battery's voltage and the alternator's output voltage will provide a faster charging rate.
As long as the engine is running, all of the power for the accessories is delivered by the alternator. The battery is actually a load on the charging system. The only time that the battery would supply power with the engine running is when the current capacity of the alternator is exceeded or when engine is at a very low idle.

 

Comment with regards to straight up gauge. If you notice all three gauges go straight up when you start the car. My senior jag tech told me that was a default that all of the guages go staight up at start. I had asked him about the oil gauge with regards to other gauges in my other cars show actual readings. Low idle+low flow/pressure higher idle= higher flow/pressure. He explained it to me it was a peace of mind kind of thing. You decide if I was fed a line considering who USUALLY buy Jags really don't plan on working on them.

 

Dropped the car off Friday with my mechanic. Diagnosis: alternator. $564.46 later the car is running fine. Sidebar: seemed like a reasonable price. We had A Hyundai XG350 that needed an alternator a while back and the cost was similar.

 

Good to hear the alternator fixed your problem chaz. You may be eatin wendy's instead of fine dining for a month, but at least you'll be able to illuminate the road in front of you consistently! lol That's a little disconcerting that an alternator would fail so soon, what is your model year again if I may inquire?

 

In the future you may want to keep your local auto electric shop in mind. I had a starter on my xk8 rebuilt for less than $100.00.