How to Test the Blue Wire on a Trailer Brake Controller on a 2004 Dodge Ram

Question:

How does the controller know that the trailer is their? how can I test the blue wire is all the way back? can a Volt meter add enough load to test this?, I might have a broken blue wire going back to the seven pin plug, just looking for an easy was to trouble shoot this I have a dodge 2004 , look like all the wiring is there?

asked by: Joe

Expert Reply:

A brake controller like the Prodigy, # 90885, will send a small amount of voltage back to see if a trailer is connected. The load from the magnets is what it is checking for. You can test the blue wire behind the controller and at the 7-Way with a meter.

To test the blue wire at the controller you will need to sever the wire a few inches from the back of the controller. Use your meter to test the end of the blue wire coming out of the controller. It should show voltage when you fully apply the manual override. If it does not you know that something is wrong inside the controller and it will need to be replaced.

To test to see if voltage is going all the way back to the 7-Way, have someone sit in the truck and apply the manual override while you test the pin in the 5:00 position. If no voltage makes to the back you know there is a break somewhere in the wiring (provided the blue wire goes all the way back).

On some Dodge Rams that came with a factory 4-Way connector, the blue brake wire does not go all the way back, it stops at the connector that is located under the drivers side wheel well. I have included a link to our brake controller installation troubleshooting FAQ.

expert reply by: Michael H