Troubleshooting New 4-Way Install Where Stoplights Stop Working

Question:

I am trying really hard NOT to make myself go bald from pulling my hair out over this small old boat trailet that I recently acquired. Someone cut the 4 flat off of the boat at the tongue of the trailer so I hooked up a temporary 4 flat plug on it just to see if anything worked. Everything works except the brake lights. Side markers and tum signals and parking lights are fine. I thought maybe it was a bad ground so i sanded the little hole area the screw goes in, nope it didnt fix it. Being a female, I dont quite understand how or where to put the light probe thingee to check things. Ive watched the video on your probe thingee and still dont understand where to put little clip and then the end of probe. I will attach a pic of my temporary set up because maybe its wrong. I am also attaching a side by side pic of the old and new 4 flat ends.

asked by: Michelle

Expert Reply:

If your turn signals are working but the brake lights aren't that's pretty odd as that signal is carried on same circuit. It looks like you matched the colors correctly in your pictures too. Since typically this issue is a weak ground and you did try one thing to help with that I would also try cleaning the pins of the 4-way on your vehicle as well.

Also you might try checking to see if the circuits work with the vehicle running. Sometimes having additional current running on the circuits gives it more "juice" to activate a circuit that draws more amperage which the stop lights does draw the most.

expert reply by: Jameson C