70-71 ebody's used a variable speed switch not a 3 speed. There are 2 separate connectors that go on the switch. One has around 4 wires the other just 2. A 3 speed switch will cause a dead short and start smoking the minute you put the second plug on it. They will work on 1 speed if you leave the 2 wire connector off. The way I know this is they had the wrong switch in mine when I bought it and it would only work on 1 speed and park. I found the 2 wire plug off and thought that was the problem. Wrong quite a surprise when it started to smoke. It had the later 72-74 3 speed switch. The trick is the plugs are the same for the switch but where the wires go are different. The wiper motor itself is the same and will work either way, Lol

Here's a factory switch which I believe was used no matter which dash you had.

https://www.ebay.com/itm/Mopar-1970-71-E-Body-Variable-Wiper-Switch/223670458910?