My Garmin Zumo 550 has been hooked directly to 12 VDC for 5 years with no ill affects. Any voltage regulation must be in the unit itself.

I don't know what years are affected, but it has been reported that some cigarette lighters have been wired with the polarity wrong.

 

thank all of you for your reply to my problem. got the thing working and the key was to use a lighter recepticle as a connection . the unit did not fry and it works great. i did want it to work only while the bike was running and the recepticle does have a power step down. thanks to all and i know my fix is as clear as mud