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I would look at the pinning you did for the new switch harness.

Everything goes through there and if you mucked any of the pins up you will get unpredictable results.

I replaced my switch harness many years ago and went through this trouble shooting. Putting the left blinker on and the horn going toot toot toot :)
 
The Ford switch harness I put in my car about 15 years ago had the wires mostly the same as the old ones I removed but some were different.

Did this new harness map 100% to the old harness?
 
1 - 4 of 16 Posts