77 blazer electrical problem need help please

I have a 1977blazer with 350 4x4 my problem is electrical of course and i cant figure it out so hopefully you guys can.My wiper switch i turn it on and get nothing but sometimes it does work and when it does work i have
noticed that the voltage guage drop alittle as your moving it from fast to low then after about 4 seconds it blows a fuse also the windshield wiper pump doesnt work when the switch is on.Now i put a pump from 1990 blazer on mine and when i did that i had to cut the wires to adapt the connections now i had it on and everything was working and two of those wires touched which did something to it and hasnt worked since. Thanks to all that respond
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