It shouldn't be doing that
I towed using my 98 Tacoma for the first time yesterday. I noticed the controller (Tekonsha Prodigy) was reading voltage the entire time (varied from .5 to 2.0 on fairly level ground, up and down hill) It seems like this means it using the trailer brakes while I'm pulling the trailer. Is this correct? Why wouldn't it read 0.0 while pulling (except for downhill) and apply voltage only when brakes are applied?
Controller is installed at 45 deg. angle (range is 0 to 70 deg.) no instructions for calibration other than brake voltage/lockup were included.
Thanks for any help.
Brian
In the 5 years I've had a Prodigy installed in my vehicles (first a Jeep, now the Tundra), the only and I mean only situations where I've ever seen the unit display output voltage is (1) when I apply the brakes or (2) when I activate the manual switch. A correctly operating controller displays just a "C" (meaning connected) until the brakes (or manual switch) are activated...it never displays any voltage (not even zero) without brake or switch activation. You are thus indeed surmising correctly...the controller was indeed sending a small amount of current to the trailer's brakes all the time and those brakes were undoubtedly being lightly applied. Not good!
So unless something is really wrong with the unit itself (which is doubtful), I strongly suspect that somehow you've got the Prodigy's red (brake switch) wire connected to some power source that's constantly providing activation voltage to the Prodigy.
First, be very sure the Prodigy was correctly connected into the truck's wiring (red wire to the
cold side of the brake switch). If this wire is connected to the hot side of the brake switch, you'll get the exact symptoms you're reporting.
Assuming the Prodigy is indeed wired to the cold side of the brake switch, the next likely cause is you've got a poor ground at one of the taillights...on either the truck or the trailer...which is causing some current to backflow through a brake light and then to the cold side of the brake switch. This is not an uncommon situation on older vehicles and trailers....all it takes is some corrosion on the ground wire of one of the taillight assemblies. Note: You'll need to check the grounds on both truck and trailer taillights.
If the taillights all check out good, then another possibility is there is some kind of electrical leakage in the turn signal switch that's allowing a bit of current into the brake light circuits (turn signal switches are supposed to isolate the brake light circuit on the side you have chosen for signalling...but on an older vehicle that isolation could break down).
Assuming the problem wasn't the first one above...a miswired Prodigy installation....the bottom line is you'll need to get out a voltmeter and start looking for voltage where there shouldn't be any. Start on the cold side of the brake switch when the pedal is not depressed. Then go check the taillight ground versus the frame. Sooner or later you'll find current is going where it's not supposed to be.
