Troubleshooting Trailer Wiring for Fleetwood Pop-Up Trailer and 2003 Mazda B3000 Pickup

Question:

I just purchased a Fleetwood pop-up trailer that has a 7 pin RV male plug. My 2003 Mazda B3000 Cab Plus Dual Sport has a factory installed 4 pin flat connector. I bought a 4 pin to 7 pin adapter and installed it, but my brake lights wont work. Do I need the Curt C56175 converter to make this work or do I have a short somewhere?

asked by: Ray L

Expert Reply:

A potential cause for your issue is a weak ground connection. Trace the white ground wire from your 4-pole back to where it attaches to the vehicle frame. This ground must be secured to a clean and rust-free spot on the frame. If necessary sand off the rust/dirt from that grounding point and reattach the white ground wire or relocate it a new spot.

If this does not correct the problem then I suggest you next test your existing 4-pole trailer connector on your Mazda to confirm it is functioning. If this is an original OEM harness it may after years of use be damaged or corroded. If it is an aftermarket harness it may have developed an intermittent connection at the splicing points (behind the vehicle tail lights) or may have been damaged. Testing will confirm. If the correct signals are present on the wires but not the connector, then the connector is bad and needs to be replaced.

You will need a circuit tester like # PTW2991. I have linked you to a video that demonstrates the process of testing a 4-pole trailer connector. I have also linked an article that includes helpful troubleshooting tips for 4-pole installations. Disconnect the trailer and test the vehicle connector. If your 4-pole does not have the correct running light, stop and turn signals on its pins then you can check several things.

Check under the hood in the power distribution box for any fuse/relay locations labeled tow or trailer to ensure the required value of fuse/relay is installed. There are variations in what different auto makers consider a tow package, and sometimes required fuses and/or relays are not considered part of the wiring package. If all requires fuses and relays are in place and you still have no signals at the 4-pole, then you can move on to inspecting the 4-pole connector.

In this case you will be better off installing a 7-way/4-way vehicle side connector to mate with your trailer; this will allow you to skip the adapter and to have the flexibility to use either type of trailer connector. You can use part # 37185 from Hopkins, which includes the 7/4-way connector, mounting bracket and hardware. If your 4-pole wiring is good but the connector is bad, then you will cut off the two 4-pole connectors, at the vehicle and the Hopkins 7-way, and splice the white, brown, green and yellows wires using butt connectors like # DW05745-5.

If you cannot activate the existing 4-pole you can install a wiring harness like Curt # C55325. This harness is a plug-and-play type that does not require you to cut and splice wires. With this harness in place you can simply plug the 4-pole into the Hopkins 7/4-pole vehicle connector which will allow direct connection of your trailer without an adapter.

Since your trailer has a 7-way RV-style connector there is a good chance that the trailer has electric brakes. If you look behind the hubs and see two wires going into the back of the hub then these wires indicate the presence of electric brakes. If your trailer is equipped with brakes you should not operate it without installing a trailer brake controller such as the Prodigy P2 # 90885. If there are electric brakes, you will need # ETBC7 instead of the Hopkins # 37185. The linked article and video cover the installation process for the ETBC7. Once you have installed the ETBC7 you can add a brake controller of your choice, like the P2 from Prodigy, part # 90885.