I wanted to convert my 69 Roadrunner to air grabber setup so I purchased a 3 speed wiper motor to swap out my 2 speed unit. I purchased a new wiring harness for under hood and everything plugged in fine. I was told the dash switch would just plug into the existing wiring but the terminals are different on the back of the switches. Did I just purchase the incorrect switch or did I get incorrect information on the interchange? Any suggestions?

If your plugging a 3 speed switch into a 2 speed wiper dash harness its not going to work. Different plug configuration and the 3 speed has a resistance cable built into the dash harness. Do you have the FSM?

Edit: this is the Rallye Gauge 3 speed connection. 2 of the single leads go to the Washer Pump switch.

I have not done the conversion but have looked into it. According to the thread below you are correct, the switch should plug in.

The 3spd switch# is 2864014. Is that what you have?

https://board.moparts.org/ubbthreads/ubbthreads.php/ubb/showflat/Number/8119820/site_id/1#import

So U really think a 2spd switch will operate a 3spd motor,that's like saying a 3spd shifter will work a 4spd.

I converted mine over several years ago. I needed just a three speed switch. The harness plugged right in.

Correct, the 68-70 B Body 2 to 3 spd wiper conversion only requires the correct 3 spd switch, 3 spd motor with correct 3 spd motor arm, the wiper linkage is the same under the dash, the dash harness has provisions for either switch...