Proper wire gauge

DO NOT TEST trailer wiring with the vehicle: Eliminate the vehicle of any flaws by testing with a battery. You have access to your wiring, a portable battery, and voila! easy testing. I never use the vehicle to test after a copper "hair" blew a fuse in my Trailblazer. Yes, I was lazy. I spent a couple of hours screwing around until I got smart and used a battery. The fuse was a real dog to find; under the back seat. LOL.

Here is more on the subject: vintagetrailertalk.freeforums.net/thread/11040/testing-trailer-wiring

A 14 gauge ground is ample for your inside wiring and also tow wiring. I often run heavier gauge up and into the trailer ground bar/bracket from the frame. All of the 12 volt grounds connect at the same bar/bracket, grounding the 14 gauge inside system. I also use a little heavier hot wire (10gauge min) to the trailer fuse block. That gives you plenty of "extra" amperage should you ever need it. In other words, say your system is working well but you want to add a high amp draw item. The heavier hot provides plenty of amps to operate another circuit...

Brake wiring is 12/2 in a sheathed cable. I think you should change it out. 12 gauge is what almost all travel trailers use on brakes. You can buy the cable at any RV shop and most battery shops.

BATTERY wires should be a minimum of 10 gauge; I often go with 8. Some Progressive Dynamics converters require 6 gauge, including a dedicated chassis ground to the frame. I say for a simple system, you can probably be safe with 8 gauge.

It usually doesn't matter which wire does what with brakes. The wires operate a magnet, either full circuit (on) or off. With your 14ga wiring already in place, check to see that the brakes actually work. That's a big question you want answered. I pick one wire location on each brake for hot and use the other as a ground, with the hot/ground in matching positons. White is normally ground on brakes and black or red is hot.

ALSO: Study your systems as you go. I wire all my trailers for a heavier system(s). Incoming wires for both the 12 volt system and 110 system are heavier than need be. Each supplies the breaker box or fuse block, with circuits going out from there.

In other words, all 110 main Romex wiring should be 10 gauge into the breaker box. That doesn't mean the trailer has to have a 30 amp inlet but that it will be READY to accept one in the future. Here is the sequence: 110 15 amp vintage style inlet. 12ga wires to J box with an access lid. From this J box, 12 ga wiring wing nutted to 10 ga wires to the breaker box. To upgrade to a 30 amp system, install the inlet with 10 ga wires to the J box. Wing nut to the breaker box 10 ga wires and it is a done deal. Cool huh?

The inside 12 volt system is mostly 14ga automotive stranded wire from the fuse box. The only difference would be the incoming wires in an upgrade. If you want to add a converter, the supply wires should be heavier gauge than if you are using a simple battery maintainer. Converters can put out a lot more amperage than the maintainer, so you want heavy supply lines.

I've been pleased with the above upgrades. Easy to do, wiring is already there and a quick job.