I've got a 1970 914, and the splines on the wiper motor shafts were hosed. I installed a later wiper motor, (well, jkeyzer did it) and expected it to work. The terminals arranged the same, and it LOOKS like it's a straight swap.
The early switch supplies power in the off position on a green wire with white stripe. This goes to pin 31b of the wiper motor. This appears to be for the purpose of parking the wipers after the switch is turned off. On the early motor, this wire goes into the third terminal of the wiper's internal rotary switch.
The late motor still has 3 terminals on its internal switch, but the third one is not used, and terminal 31b goes to the second terminal. The unused terminal is grounded to the case. I opened up a spare late motor, and found that the internal switch grounds pin 31b. Grounding a hot wire of course leads to fuse blowage.
Does anyone know a way I can rewire this late motor to an early car, so I can use it? Here's the catch. The fresh air box and gas tank are already in, and the tank has gas in it. I'd REALLY like to figure out a way to rearrange the wiring at the motor and/or the switch that doesn't involve removing the motor.
I've looked at early/late wiring diagrams, and so far all I've done is give myself a headache. The car is a 70, and the motor is unknown, but clearly different.