1997 F 150 wipers won't stop

I have a 1997 F150 4x4 that the wipers just started going one day when I started it up and won't stop. I replaced the turn signal/multifunction switch and the wiper motor but still same problem. I have heard it is possibly defective GEM. Any help would be appreciated.

Most common for this is a leaking windshield. It has either caused corrosion in the fuse box or gotten into the GEM that is mounted behind it. If it was mine I'd take a phone photo of all the fuses and relays that plug in for later reference, disconnect the battery and then remove the fuse box to get a good look at the back and clean all the connections. If the fuse box, which cleaning is cheapest, isn't the problem, unfortunately the GEM is more likely the item that has gone out. If you don't fix the leak it will happen again, so be sure to get that taken care of.

No sign of it leaking. Windshield has been replaced a year ago. Checked fuse box and it looks ok. See no sign of corrosion on fuse box or GEM but I have ordered a GEM so hopefully that will fix it. Thanks for your reply.