Probably not the cause, but if you have never had roof serviced, check out Halfords silicon spray and grease- get the merc spec from one of the site moderators, but clean and grease up all the moving roof parts inc the roof itself plus the microswitches etc in the front of the A pillars and all the roof rubbers- the first time I took my mom out for a spin with the roof down, the roof wouldn't operate and jammed, so I had to push it gently and it closed- she was going to get out and get the bus home. I was well fed up. but reading up the site, I decided to clean all the roof parts and it was just lack of maintenance. You never know, but before looking at the relays and other stuff ask someone like jbanks, the site moderator, for the correct spec and get some silicon spray and give the roof a service. cost you about a tenner than look at other options, if not cured. the first and only time my roof failed, you can bet I went to town with the spray and I lube it all up about once a month.. but then I clean my car more than I use it. regards kevin.