Slight Misfire?

[chimaera]

Hello All,
Am having a bit if a problem with my 1993 4ltr Chimaera. At around 2750 - 3000 rpm I get a misfire and splutter, however it only happens when the radiator fans are on and when using a slow throttle when accelerating/at steady throttle. It does'nt appear to be temperature related as I have a fan bypass switch and even if the engine is cold and I turn the fan on the engine misses. I suspect that it may be the alternator on it's way out as occasionaly the red light on the dash comes on very dimly (can only see it at night) and with the electrical load up this is when it misses. Any advice before spending £250 on a replacement!!
Cheers,
Scott W.

[chimaera]

Thanks for the ideas, Just a note about switching the fans on and off, Although on initial turning on there is a slight dip in revs at idle it takes it in it's stride when driving round, I only get the misfire at 2750-3000, this is what is confusing me as I thought I would either have a misfire all the time or not at all.
Will also look at the igintion switch connection (I am assuming this is the one on the steering coulmn, or is there a hidden one?)
Thanks again.
Scott.