RED DOG and ala_xfire have made excellent points. Also, could there be interference from a device that is on only with the engine running, outside of the alternator? An alternative method of checking for voltage spikes from the alternator would be swapping alternators or regulators, since Stu292 has more than a few of those.

Stu292, have you read error codes? With 22 Crossfires for sale, I would think that you have the proper diagnostic tools...

Stu292, please follow up with your findings - this could be very helpful for future readers with the same problem.

Klaus

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