Yesterday I fixed the front of the trailer wire harness as the previous owner had cut off 4 of the plug and butt joined a 4-pin connector.
I then modified a
7-pin replacement harness to connect to the trailer harness (note, the dang Chinese manufacturer of said replacement trailer connection didn't follow the standard wire colors for the connections and I had to test them out). I added 'Y' splitters to the trailer harness so either the civilian or military trailer plugs could be used (the trailer didn't come with the military plug, but I used one that Silverstate55 had very kindly repaired and given me last year). The cover for the electrical bundle was also missing, but I had saved one from an old, short bodied pioneer tool trailer that I sold last year as well. I drilled the frame holes larger and added nutserts to mount the plate (two on the top and two on the bottom of the frame rail - and yes, I did put copper anti-sieze on the bolts in the nutserts as I don't fancy them rusting into place).
Mostly in the dark last night I finished the safety chain upgrade. The original safety chains were also 3/8" in diameter, so I used the same size, just Grade 70, zinc yellow with safety clip hooks as well. I had to replace the chain mounting bolt as when I removed the original bolt I damaged its threads (it was rusted in pretty good, and even with the nut on the end of the bolt when I pounded it out, the threads were still damaged). The replacement is 7", grade 8.
I kept the original chains off the trailer as they were in perfect condition, and used a set from another short bodied pioneer tool trailer that I parted and scrapped out nearly two years ago as it only had one chain anyway (I only needed the mount and big loop on said mount). The original chains were 16 links long, the new ones are 24 links long to properly reach a truck using a receiver hitch.
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Today I verified continuity from each of the trailer plugs' pins to the appropriate wiring at the taillights. I then set my iPad behind my trailer on a stool and "Facetimed" my cell phone. I was able to sit in my pickup and verify all proper brake, signal, tail, and hazard light functionality. This was so I could perform the check by myself, without needing to bother someone else.
Then I drilled two new holes for nutserts on the inside of the trailer tongue by the military plug holder to mount the 7-pin holder (in retrospect, I probably should have looked for a nicer 7-pin plug holder, this one is pretty cheap, but serviceable I suppose). Which ever plug, military or civilian, isn't being used will need to be wired down to ensure it doesn't bounce out and drag on the road.
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Finally, I'd like to fix the trailer cable mount point near the lunett.
Here's an example of the one still present on my rusty 1976, large bodied pioneer tool trailer:
Which the bolt is clearly broken flush on the M101: