Think I have a bad or intermittent backup light switch on my SA trans.
It’s shape suggests it can be removed with a wrench but before I try that I’d like to see if someone’s already done it.
Thanks!

 

yeah they're just threaded in but i've never had one stop working tho.

 

Disconnect the wires going to the switch an ohm out the switch when the car is in reverse and when it is out of reverse. I think you should have continuity when it is in reverse.

 

Thanks, this one is intermittent, just needs to be taken out and cleaned probably

 

Try cleaning the connectors on the harness side of the switch. Once, my connectors were so badly corroded that I had to cutoff a few inches on the harness side and solder on new leads. On my S5, these switches typically have a limited lifespan. I'm going on 3 years with current my backup switch (Mazda p/n 8130-17-649D) and it recently stopped working. Time for another replacement. I once measured the contact resistance of a bad switch and it was somewhere in the vicinity of 8-10 ohms. It doesn't take a lot of contact resistance to render these switches inoperable.

 

Consider also that these trans mounted switches REQUIRE a copper crush washer of the proper dimension to be installed which spaces then switch arm properly. If the crush washer is left off (*lost on disassembly, or removed for some reason), the switch plunger will extend too far into the trans which allows it to be hit by the reverse gear rod, bending or breaking the tip - and the switch stops working.

The switch threads into the transmission easily, so don't over torque it. The crush washer is for spacing, not fluid retention. Most reverse gear switches get damaged on trans removal through having the wires ripped out, or torn off flush with the resin sealant, rendering them inoperable. Note that the 4 wires are made to specific length to prevent improper attachment, but they simply close contacts, so not critical for polarity.

I believe the Reverse Switch also functions as the 5th gear switch on GLS-SE fuel injected cars to trigger closed loop fuel injection mapping, as the rod is in a different position when in 5th, but need someone else to confirm that.

 

There is a separate switch for 5th gear, used for activating max split air (via solenoid/ACV). I don't believe it is explicitly monitored by the ECU.