Intermittent Wiper problems

I have a 2001 Toyota Sequoia that started having problems with the intermittent setting on the wipers. It is now to the point that it runs just like the slow wiper setting with no delay, it also doesn’t “park” the wipers when turned off. I found that with the ignition in ACC position the wipers work perfectly (intermittent works and wiper “parks” properly when turned off) but when the engine is running I only have a Low or High wiper speed and no “Parking”. I have researched online and most say to replace switch or wiper motor but both work with engine off so I am wandering if it is being overpowered with the engine running. Any suggestions?

I have to wonder if the alternator is causing the issue due to excessive ripple voltage. You could disable it by removing the small connector on the back side of the alternator then start the engine and see if the problem still occurs.

What about if the ignition is put in the RUN position but not going past that to START and actually starting the engine? Does RUN react the same as the ACC position?

Thanks, I’ll give it a try, but wouldn’t that cause problems with other motors (electric windows, locks, etc.)?

Twin Turbo, yes the wipers work correctly with key turned to ACC or Run, it only happens when the engine is actually running