Sequential tailight problem
 

I bought some sequential tailights from American Muscle for my 1997 Mustang GT. At first they worked great, then without warning the drivers side started started running way fast, then back to normal, then way fast, and back to normal, repeatedly. Not everytime I used them, only once in awhile, but it's really pissin' me off.

I'm from the old school, I didn't use the 'wire nut connectors' or the 'quick-splice connectors', I striped the insulation and spliced each connection and finished up with electrical tape. I'm at a loss and any help would be greatly appreciated.