98 xc - Lights dim for split second / Flicker?? Any ideas?

You say there is no change in the engine idle speed but is it the radiator fans starting up when the air con cuts in??

My Focus does exactly the same thing, only alittle more pronounced when the fans start.

Tim..

Sounds like a bad ground connection near the battery. It could also be a bad connection on the hot line, but less likely. The other obvious thing is a bad connection to the voltage regulator or a bad voltage regulator. Batteries can also get bad connections internally.

I don't think it is the dimmer relay since that wouldn't affect the dash lights. Also, I don't think it is the instrument voltage regulator since that wouldn't affect the headlights. This problem would be easily visible on a voltage meter.

That is what I am thinking also. I will look for any loose connections. I am sure that I will notice it on a meter but is there a way to rule out a voltage regulator vs battery and such.

I made sure the AC was off. It still happens.

Can you hear any relays clicking either on the bright to dim or the dim to bright parts of this cycle? It almost sounds like an electric motor is trying to start up but is having an awefully hard time (to see this effect try closing a closed window... I only notice it on the headlights tho)

If the dimness continues for a while it could mean this motor has got itself spinning, but is having a hard time turning... I agree with the one post to check the cooling fans on the radiator, motors act almost like they are shorting out when they aren't turning.

The best way is to take off the battery terminals and clean them. If that doesn't fix the problem, take off other key connections to the battery cables and voltage regulator and clean them. If that doesn't work, get your electrical system tested. This will check out the battery, alternator, and regulator.