After another frustrating commute I decided to study the XP8000 a bit more. A magnifying glass and bright light showed that the 12 volt connector I was using appears damaged (this was a Woot purchase after all). The little gizmo at the bottom of the connctor that engages the ridge at the bottom of the plug is bent against the bottom. Preventing the plug from fully engaging. The 18 volt connector has no problem.
A ittle time with the soldering iron and I had an 18 volt adapter. A bit of research seems to indicate that MR16 LEDs are compatible with 12 volt AC. It seemed safe to assume that the lights would work at 18 volts DC, and be even brighter. So I hald my breadth and plugged in the 18 volt connector.
A short test ride seems to have solved my problem with vibration but tomorrows commute will tell.
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"Why is there a hill after every meal, but not a meal after every hill?"
--Overheard on Grabaawr