Thank you...

No, impossible! the light / main system is the problem, but to be sure,
check each sender, take a compressor, aply light pressure with a tube to
each openning, put a voltmeter and check the sender, they should close or
open depending on the one you check.... anyway, changing those sender is a
must unless they are new...

Like someone said, a faulty ground or wire must be the main problem

Regards, Ben
http://www.benplace.com/