Troubleshooting Blinking Trailer Brake Lights on Trailers Towed by 1998 Dodge Ram 3500

Question:

I have a 1998 ram 3500 diesel with factory trailer wiring plug in under the dash. I hooked up a new hayes controler thinking that the old one may be bad but the problem is still there. When the truck is turned off it will flash a quick one second surge of power every 15 seconds or less. Depending on trailer it will illuminate the brake lights on the trailer or you will hear a chirping from the trailer brakes themselves. There is no flashing on the truck lights themselves. If you put a test light on the truck 7 pin trailer connector to the negative and brake wire pin you will get this quick flash also. Any ideas, this has done this since the truck was new in 98. I have just pulled the under hood fuse when not in use since it drains the battery down.

asked by: Chris L

Expert Reply:

The problem you describe leads me to suspect a problem with corrosion within your vehicle wiring. Since multiple trailers have similar problems the vehicle is the place to start.

I suggest you carefully check the trailer socket on the truck, inside and out, for any signs of corrosion or damage that could be causing a short-circuit. Also check the connector that plugs into the back of the 7-way for the same type of issues: trapped dirt or water, or corrosion that could be causing two separate circuits to become bridged together.

For example, on a 7-way socket the pin at the 1-o-clock position (see photo please) is next to the pin for the trailer's right turn and right brake light. Corrosion in the socket or upstream of it in the vehicle wiring itself could cause the 12V power feed to bleed over to the brake circuit, causing the lights to come on.

You can also test upstream at the under-dash harness that connects to your brake controller. One of the four pins on that connector should carry a constant 12V signal (this is the pin/black wire that brings power to the controller from the battery). Another pin, the one for the red wire on the controller, should carry a signal only when you press the brake pedal. You will need a circuit tester like # PTW2993 to test.

expert reply by: Adam R