Test Brake Controls

Technical Bulletin

PROBLEM: Lack of braking at maximum gain setting.

SOLUTION: First verify the following:

Trailer is plugged into tow vehicle
Gain is set to max
Trailer brakes are adjusted according to manufacturers specification
Battery voltage (approximately 12-13 volts) between the Black power wire and the White ground wire at the rear of the brake controller.
- This is the input voltage.

With manual slide lever fully applied, measure the voltage at the wheels of the trailer. If you have 11 volts or more, check the trailer brake adjustment. If brake adjustment is within specs, check brakes for mechanical issues.

If the voltage at the wheels is less than 11 volts, unplug the trailer. Then, connect ground clip of test light to the ground pin in the trailer connector on the tow vehicle and contact the probe of the test light to the Electric Brake pin. With the manual lever fully applied, using a volt meter, measure the voltage between the Electric Brake pin and the ground pin. If the voltage at the rear of the tow vehicle is 11-12 volts, repair or replace trailer wiring or brake magnets. If voltage is not 11-12 volts, relocate the ground probe of test light to a known good ground on the tow vehicle and retest. If the voltage is not 11-12 volts, repair or replace ground wire to trailer connector. If voltage is not within this range, check the output voltage at the controller.

To check the output voltage at the rear of the control, cut the Blue wire 5-6 inches behind the control. Install the test light between a known good chassis ground and the Blue wire coming out of the control. Apply manual slide fully; using the volt meter, measure the voltage from the Blue wire to chassis ground. If the output voltage is within 1 volt of input, control is good; repair or replace Electric Brake wire on tow vehicle. If it is not within 1 volt of input voltage, measure the input voltage again, from the Black wire to the White wire of the brake control, with the manual slide not applied. As you are measuring this, fully apply the manual slide and monitor the voltage. If the voltage drops, there is a voltage supply issue to the brake control. If the voltage spikes, there is a ground issue to the brake control.

Manufacturer: Tekonsha

Bulletin Date: 10/10/2007

Bulletin Number: TB0004

Updated By: Dani S.

Lasted Updated: 3/1/2021

Todd V.

7/19/2023

So I’m measuring about 1.0 volt at the TV trailer plug with no brake activated, and 10.7 when the controller is on full. I realize 10.7 is less than 11, but it seems close enough. Is it? It’s a brand new Ram 2500 Cummins towing a Mirage #10k utility trailer. The trailer’s brakes are underperforming (unable to lock up), so I’m going through the check list. Next I will take a peek at the brake shoes and see if I greased them by accident.

Mike L.

8/2/2023

@ToddV A brake controller will send a small amount of voltage to the trailer in order to 'read' whether a trailer is connected. With the brake controller turned up to full gain, without a trailer plugged in it's not unusual to get 10.7V at the trailer plug. Plug in the trailer, pull the manual brake switch on the brake controller and check voltage on the blue wire immediately behind the trailer connector. You should see closer to 12V there. If you test at the brake magnets, you should see around 10.5V, but no less than 10. I'd also recommend checking to ensure the trailer brakes are properly adjusted. Hope that helps!

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