Why Are Boat Trailer Taillights Not Functioning With 4-Way to 7-Way Adapter on an RV

Question:

I have a 2007 Class A motorhome bought it used and want to tow my boat. The motorhome has a factory 7 blade round female end My boat trailer is a 4 pin flat. Is there an adapter I can get that works properly ? I bought an adapter from a local store but the trailer lights dont work properly, especially the left turn signal and when turn signal is on all the marker lights pulse The boat trailer lights work perfect towed behind my SUV which has a factory flat 4 pin, so its 4 flat to 4 flat But I cant get the lights to work going from 4 pin flat to the 7 blade on the RV Thx

asked by: Randy

Expert Reply:

One of two things are happening. Either the 7-way on your RV isn't wired right and needs to be addressed or the grounds of the light assemblies on your trailer aren't sufficient. This is the most common problem that causes the issues you are describing. I would check the ground for each light assembly and the main ground strap that runs from the trailer connector to the trailer frame. Make sure they are securely attached to a clean metal surface.

If that doesn't fix the problem you will need to use a circuit tester like our part # 3808 and test all of the pins on the 7-way for voltage in the correct places. Use the diagram I attached as a guide.

expert reply by: Jameson C