I've got a 2001 XJ8 with a pulse in the lighting system. The dash lights will phase from bright to dim in tandem with the sound of the engine. If I turn on the headlights they too will surge in sync with the sound of the rotation in the engine, but the headlights do not need to be engaged to see the effect. We have checked for clean grounds throughout the engine compartment and cleaned the ground where the engine grounds to the body beneath the passenger floor, checked the pulleys for drag, replaced the belt & water pump (for other reasons) and all four o2 sensors. The alternator is just over two years old (new battery at the same time) but this problem existed mildly prior to the alternator change. The only thing we have been able to do that alters this situation is removing the 5 amp fuse that is related to the alternator. When the engine runs straight from the battery, the lights are bright and steady. As soon as that fuse is put back in place the surge immediately starts again and lights pulse. The fuses are good. We also checked the cables running from the alt to the starter & starter to battery and don't see any indication on the amp meter to indicate that these might be the cause of the problem. The amp meter on the battery terminals reads 12.30 with the car off, with it running it's between 13 - 13.66 with the occasional jump to 14.

Any ideas on what might be causing this that we haven't already ruled out would be greatly appreciated!!

sorry had this posted in the wrong area. Thanks Woox4

 

Sounds like the alternator may be the culprit here due to a possible open or shorted rectifier (diode).

 

ok, but as the old Alt was doing the same thing could something be killing the diode right after install? i will order a new Alt and do the PITA install as i have done it before. but just wanna know if i should look out fore anything that could blow the diode before hand.

 

I find it best to take the existing alternator to an automotive electrical shop equipped with the test instruments to determine if the rectifiers (diodes) are shorted. I personally have not had good experiences with the 'remanufactured' alternators available from some parts houses.

I have also seen at least two alternators that had unevenly worn commutator areas causing the brushes to make irregular contact. The symptoms were similar to what you describe. The fix was to replace the armatures and brushes/rectifier assemblies.

 

alright, good enough. my wife also said another odd thing is happening when she uses the stock cd changer in the trunk the speakers on the passenger side cut off but just using the radio they work fine. is this another issue from not enough power or a totally different issue?
also have a gremlin in the telescopic in the steering column.... I will hunt him down later.. (already read a thread on here about that.)