WilkinsJ, the back up switch is on driverside up by shift tower. You will need 22 mm deep socket to take it out.
Buy some contact cleaner with lubricant and contact cleaner that dries.
Home Depot carries CRC brand it will work fine.
Spray the ball with the contact cleaner lubricant, you can use this on the connectors also, then spray connectors with the contact cleaner that dries.
This brought mine back to life and it is still working plus it will save you sixty plus bucks.
P. S. Push ball in and out so lubricant can get to contacts inside of swtich.