Grabbing or Locking Brakes
•
Check for contaminated brake linings.
•
Check for weak or broken brake shoe return
spring.
•
Check for rust on armature plate or brake drum.
•
Check for improper controller installation.
ELECTRICAL
VOLTAGE MEASUREMENT PROCEDURE
To measure voltage, connect the voltmeter to both magnet wire leads while the towing vehicle is connected and the
engine is running to insure accurate readings. The voltage should begin at O as the controller is increased slowly to
approximately 12 volts. If the controller does not produce this voltage control refer to your brake controller trouble
shooting and information manual. The lower reading will provide smoother braking while the higher may produce
sharp or severe braking.
AMPERAGE MEASUREMENT PROCEDURE
Amperage is the electrical current flowing in the brake system while the magnets are energized. Make sure of your
ammeter’s rating to prevent damage to meter. An easy place to check the amperage is at the output wire from the
brake controller to the brakes. Disconnect this (blue) wire and put the ammeter in series into this line. Please refer to
the following chart.
Individual amperage draw can be measured at the magnet by inserting the ammeter in the line of the magnet you
wish to check. Disconnect one of the wire leads from the wire magnet and attach the ammeter between the two
wires. Reconnect the wires when completed.
Brake Size
Amps To Magnet
2 Brakes
4 Brakes
6 Brakes
7 x 1-1/4
2.5
5.0
10.0
15.0
10 x 2-1/4
3.0
6.0
12.0
18.0
12 x 2
3.0
6.0
12.0
18.0
12 x 3-1/2
3.0
6.0
12.0
18.0
There are several possible reasons that may cause voltage variations. Listed below are the most probable.
•
Poor electrical connections.
•
Open circuits
•
Broken wires or incorrect wire size.
•
Brake controller malfunction.
•
Electrical problems can also be caused by bare wires, defective controllers or shorts in the magnet coil.
Locating the source of a short circuit should be done by checking individual sections. Should you find the amperage
reading drops to zero after disconnecting the trailer, then the short is in the trailer. If the amperage is high after all of
the magnets are disconnected, the short is somewhere in the trailer wiring.
Please note that the majority of electrical brake complaints can be traced to the controller. Refer to your brake
controller manual to insure your controller is correctly adjusted and that the connections are in compliance with the
manufacturer’s specifications.
Gravity Tender V1.0
50
