After replacing both the switch and the motor my wipers only work in high speed. The problem seems the be the module that goes between the switch and the motor has crapped out. From what I understand I can bypass it if I buy a 2 speed switch from a 84-91 and plug the black plug from the firewall into the switch. This would give me high and low speed right?

 

Bypass is a nice word for what you are doing to your truck. Junkyard maybe?

I have the EVTM manuals for a 1990 van and a 1991 truck. Maybe I could take pictures of some pages or you could try google image search.

If you change it and it quits working you will probably hate life before you can get it working again.

 

why don't you just repair the wiper control module?
only takes about 1/2 hour to open it, find the crack, solder it, and put it back together.

 

there is no visible damage to it

 

What I'm suggesting is totally reversible once I can find a box that works. From what I've read people have gone from 2 speed to intermittent. I just want to make sure that the reverse is possible.