Wiper switch issues/ and serge in tach when blinker is on

[shawn65]

So I have a few issues, #1 so I believe I have a 1 speed wiper motor. My car was missing the wiper switch so I got a NOS wiper switch. First off I did not realize that the wiper switch plug only had four connecters and the wiper switch has five. I also have a red and yellow wire next to the wiper plug not sure if this has anything to do with the wipers. #2 when I turn my signal on I get a serge in the tach. Now the tach is nowhere close to being hooked to the blinkers or near the blinkers. it works fine when the. Blinker is off. any help would be great!

 

[67Dart273]

I would try re-grounding the tach somewhere else than it is now.

If that does not improve things, measure the tach hot wire with blinkers going and not, and see if the supply voltage is changing.