Jeff, yeah, 18v is way too high - should be more around 14.8 max. Best fault finding chart I've ever seen is at eletrex website (http://www.electrexusa.com/electrosport_fault_finding.html) - takes step-by-step approach. Corrosion on the connectors is the enemy -can itself fry a regulator as resistance (and heat) build up. I hope that helps. Good luck and let us know.
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-Jim
'93 MC21