The washer pump fails to pump activate on my tailgate wiper.
What I have explored and verified:
There are no leaks in the system (hoses / reservoir/ couplings, etc)
The Windshield and headlight washers both work
The rear wiper, windshield + headlight wipers both work
The fuses for either washer / wiper system(s) are not burnt out
Both front and rear pumps work when each are attached to a 12Volt power supply
The rear pump motor will not work when the switch on the steering column is used to activate the rear washer / wiper feature -when doing this with a voltmeter applied to the plug for the rear washer motor, a brief reading of 3(+) volts flashes but then it will not register any voltage at all - the rear wiper runs for 3-4 swipes normally - When the same thing is done to the windshield / headlight washer feature the voltmeter registered 12(+) volts consistently when running .
Continuity of reservoir wiring harness- both positive(white/ black for rear washer pump and white for front windshield / headlight washer pump) is OK. The negative ( Black wire for front windshield / Headlight washer pump) is OK
There's NO continuity from the negative(Black wire) of the rear washer plug and the main 4 connective plug that couples each motor to the dash switch/electrical system. Between the black plug wire of the rear washer motor
plug and the main 4 connective plug is the reservoir level monitor and what looks like a crossover with 4 black wires. Bypassing the fluid level monitor still results in No continuity.
The rear washer line has been tested with a stream of compressed air and it is not clogged.
Short of replacing the rear washer relay, the steering column switch, and maybe the wiring harness directly attached to the reservoir, I am at a loss as far as what might be happening.
Does ANYBODY have a reasonable answer / idea as to what might be the problem? HELP!!