I just had the same problem. This post worked for me to the T!
"I just fixed the wiper problem!! It was pretty easy. The only tools you'll need are a quarter inch nut driver and a soldering iron. Disconnect the big red connector from the back of the wiper switch. The interval governor is a little black plastic box just to the left of the fuse box (behind the headlight and wiper switches). There is one bracket on the bottom rear of the module box and a single screw attaches it to the dash. Remove the screw and pull the module forward out of the dash compartment. Disconnect the black cable connector at the module. It looks almost identical to thee red connector at the wiper switch. Take the module assembly to a suitable work bench with plenty of light. Two screws hold the cover on. One of the screws also holds down the short cable assembly coming out of the box. Remove the two screws and carefully lift the PC board assembly out of the plastic box. Inspect the backside of the PC board. At one corner of the board is a large plastic relay and next to it is a heatsink with a special power resistor connected to the bottom of it. On my PC board, solder connections were broken on the heatsink and resistor leg. Carefully inspect all the other connections on the board for cracks. These are cheap, single-sided PC boards and the solder connections can break very easily, because there is no plating through the holes that the components go through. if you have an eye loupe or a magnifying glass, use them to carefully inspect all the connections. If any connections are broken, simply take some regular 60/40 electronic solder wire (the kind with a flux core) and solder any of the faulty solder connections. Of course, I also inspected the top (component) side of the board to make sure there were no burned components. On my board, the components looked fine. When finished, put the board back in the box and re-install. I did this and voilą! The delay works perfectly, and so do low and high speed wipers. I guarantee this is a common problem with these wiper modules. With those cheap solder connections, and the board rattling around in the dashboard for 20 years, this is the kind of thing that usually goes wrong. Hope this helps everyone. It was really pretty simple. "