Today was a rainy, fairly cool day and I didn’t want to sit inside all day. I have a few things on my list to do before the rally, but I didn’t want to start a big project. One thing on the list was to make an adapter plug to convert the 12 pin military trailer receptacle to a 7 pin civilian RV type receptacle. With this I can pull any civilian trailer behind the Jeep or Deuce and have running, turn and brake lights – as long as the trailer has 24v or LED bulbs installed. These adapters are available to buy, but they run about $150!
I found a couple of old military trailer pigtails in my M100 trailer earlier this month and 1 of them still had a plug end that was still ok, albeit not presentable. The cable was shot – crumbled when bent, and the metal cover and spring were rusted beyond saving. I cut the cable and clamp off and used the cable stub as a means to pound the rubber grommet out of the plug housing. Once the grommet (with pins) was out, I sprayed some penetrating oil into the grommet holes and let it soak for a minute. This made it easier to pull the pins out from the back of the grommet. Notice I said “pull them out”. If you try to push them out without the proper tool, the pin WILL bend! Trust me, I bent 2. The proper tool for pushing them out is a hollow punch the same diameter as the grommet hole and inner diameter of the pin. You can pull them out from the back side fairly easy with a pair of pliers – and lube.
Once I had all of my pins out, I got all of my supplies together: 7 pin vehicle side receptacle, 7 wire trailer cable, solder, torch and a utility knife. The 7 wire cable is what I had left over from adding trailer brakes and rewiring my Brother’s car hauler – about 2′ long. I wanted to make a 4′ long adapter, but I ended up using what I had available.
Next step was to remove the wire from the pins and solder the new wires to them. I fired up the propane torch and grabbed a pin with a pair of pliers. Hold it over the heat and pull the wire with another pair of pliers – the wire will come out of the pin when it gets hot enough.
I only needed the yellow, green, white and brown wires, so I cut the wires to length and then snipped off the red, blue and black wires. Here is how they pin out:
- White – GND – Pin “D”
- Brown – MRK/Tail – Pin “E”
- Yellow – LT/STP – Pin “B”
- Green – RT/STP – Pin “J”
Now, to solder the pins to these wires is quite simple. Strip about 1/4″ of insulation off each wire and clamp the whole cable in a vise to hold it steady. Fire up your torch, slip a pin over the end of a wire, and apply a little pressure with pliers – start heating the pin about halfway down it. The pins that had wires attached will still have a little bit of solder inside them. When the solder melts, the pin will slide down onto the wire. Then take your solder, reheat the pin and apply a little solder – it will suck up into the wire and pin. Let it cool and pull gently with pliers to make sure it is securely attached. Do the same with the other 3 wires. The white wire in my cable was a bigger wire – maybe 12 gauge. I had to trim off some of the strands to make it small enough to fit in the pin.
The last step is to push the pins back into the grommet – in their correct holes of course. The grommet holes are marked with letters on both sides. Grab a pin at the base and push it into the correct hole (using the pinout above). I put the grommet up against my vise and pushed the pins in.
Next, feed the other end of the cable through the plug housing and press the grommet all the way down, lining up the slot in the grommet with the tab in the housing. Pin J and H should be at 12 o clock. There is a notch that the grommet ring sits in when fully seated (notice the bottom ring in the pic above). I had to use a 1/2″ diameter bolt to help push the grommet down, but that might have been because of the rusty housing.
Last thing to do is secure the rubber plug with a hose clamp. First side is finished!
On the RV receptacle side, it is really non standardized. The markings on the housing tell you one color, but you end up hooking up a different wire. You really have to by the diagram included with the receptacle. It will show you which pin does which function – compare it to the pinout above. Slide your cable grommet up the wire and run your cable through the housing. Strip off about 1/4″ of insulation and hook them up (harder than it sounds – you are dealing with real short wires and small connectors on these),
Lastly, use your multimeter to check continuity on all of the wires and secure the housing and grommet.
I plugged mine up to the Jeep to test the function. Obviously I have something wired wrong because I couldn’t get voltage on either of the turn signals – marker lights worked fine. I’ll save that project for another day!
Since the metal parts on the military plug were too far gone (spring was rusted apart so the cover wouldn’t stay closed and the lock was pretty rusty too), I decided to just cut them off – I didn’t have a need for them to be waterproof anyway, so I would save some bulk and weight. The vehicle receptacle cover has a tab the fits into a notch in the rubber part of the plug to keep it from coming out – not to mention it is a pretty tight fit. I cut the cover arms off with a sawzall and ground them down with a bench grinder and wire wheel. Lastly, I shot a coat of flat black on the metal parts to keep the rust down.
All in all, I think I spent about 1.5hrs on this project and spent a total of $8.82 on the receptacle (since I already had the wire and military plug), for a grand savings of $141.18!
You can see the plug is a little disfigured, but as long as it works I don’t care!
If for some reason I need a longer cable, I should be able to install it in about 1/2 the time now that I know what I’m doing!
After I finished the cable I went ahead and changed the oil and filter on the Jeep. I ordered a couple of filters from a guy on ebay for $12 ea – delivered! Figured I had better buy a couple for that price – the last one I bought about 3 years ago was almost $20! These filters look to be in a military box, but not old – and it is WIX! The oil change went well except that I need to come up with a GOOD way to get the old oil out of the filter housing – I don’t like leaving a quart of old oil in the engine! While I was there I checked the air filter – it was pretty clean, so I didn’t mess with it.
After I changed the oil I let it run up to temperature to check for oil leaks and pressure. Then I adjusted the carb. The old engine is sounding pretty good now.
The next few days are supposed to be cold and rainy, so I will probably get back out there and work on the brakes and maybe the springs – we’ll see!