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How to Test the Trailer Light Functions of a Trailer with a 4-Way


Hello,my trailer has 4 prong3 male/1female connector at trailer tongue. Is there a dependable basic tester that will not only check for electricity at vehicle connector,but I can plug the trailer directly into to insure my trailer lights function WITHOUT a vehicle being attached. I dont have the rental truck here yet and want to insure lights on trailer work,before I pick up truck. thank you for your answer! The truck is a rental, The Pace is 2003 model CS612SA 6x12 single axle


Expert Reply:

There is, but I will warn you it's pretty expensive. The Hopkins Tow Doctor Trailer End Test Unit # HM50928 is designed to test the connector on a trailer for function and would be perfect for what you are trying to do. Check out the review video I attached.

A much more inexpensive option would be to use a jumper wire from a car battery's positive post to put voltage on all of the pins of your trailer's connector.

You would need to test the three male pins next to the female pin. The one closest to the female pin will be the running lights. This should light up all of the lights on the trailer when voltage is applied. The taillights will be dimmer but still lit. The pin next to this one will be the left turn stop/turn circuit. This should activate the left taillight brighter than the running light circuit, and finally the last pin will be the right turn/stop circuit. The same thing as the previous circuit but for the right taillight.

expert reply by:
Jameson C

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