Homemade 5 to 4 wire adapter

[woodywrkng]

In case anyone has had any issues with a 5 to 4 wire adapter for your trailer to tap into your car's wiring, here's a possible solution if you're handy with electricity.

A few years ago I purchased a Curt powered T connector so I could tow with my 2008 Scion xB. The Scion uses a separate brake light wire, where a trailer uses both turn signals as a brake light. The Curt unit worked once and then became flaky and intermittent. Curt sent me a new one and it has worked fine. I recently cut apart the flaky adapter to see what the problem was, and found that of the 10 wires entering the circuit board, only one is soldered directly to the board. The others were jammed into Scotchlock type connectors which were soldered to the board. These are known as Displacement Connectors, and I've had trouble with them in the past. I don't know for sure if these connectors caused the intermittent problems, but I was mighty suspicious, and no longer trusted the working adapter. Since I had damaged the circuit board getting the molded plastic housing removed, and wanting a spare adapter in case the working unit failed, I used the wires from the bad one and built an adapter using 4 relays.





I didn't personally come up with this circuit, but rather added the diodes on the relay coils, and LEDs that show the outputs. This is a powered adapter, which needs a 12 volt source. It bench tests just fine, and the relays make a nice solid click. The relays are Panasonic JSM1-12v-5 which cost under 2 bucks each from DigiKey and can handle up to 15 amps.

[H.A.]

Hcux

[woodywrkng]

Yeah, the taillight relay is to keep the load of the trailer lights off of the vehicle's lighting system, since I currently have standard bulbs on the trailer. If all of my trailer lights were LEDs I may have left the relay out.

I did run across a nice feature of the Curt adapter over the weekend. While dealing with a bad connection in one of the trailer's side running lights, while the taillights were turned on, I created a very brief short from hot to ground which knocked out all of the trailer's taillights. Drat, I thought I just hosed the adapter since there's no fuse in it, and the turn signals still worked. However, turning the vehicle lights off / on seemed to reset the adapter and the taillights again worked. Nice feature.