If it's a 91 with the daytime running lights I'm pretty sure it's an aftermarket add on somebody installed on their own. If they're turing on when they get wet I'd assume there's a short. Your light tester is your best friend for this! Force the issue, get everything wet and start stabbing it around the connections, backtracking till you find out where the power is originating from. If it is infact an add on that somebody installed I'd be willing to be they ran something too tight and it's shorting out on the chassis, maybe water helps bridge the gap
