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Old 12-26-2011, 08:58 AM
Durallymax Durallymax is offline
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Building Trailer Wire Test Box Couple Questions.

We have been wanting to build a trailer wire test box for awhile for the shop here on the farm.

This winter we are a little more caught up and finally have some time to get some of these projects done.

As of now we are going to be building it off of a hand truck so that it is easily portable.

The basic concept is that there will be two female 7 round pin (SAE wiring) connectors mounted in the front of the electrical box we will be making. We will then have two pig tails hanging on each side that can get plugged into each of the two connects or plugged together with an adapter for more reach.

The pig tails are one idea because we have some extras. I dont like the idea of fighting pig tails though. It would be ****** to have two reels on each side with about 10-20' of 7 wire wrapped in them. if anybody knows where i can get cheap reels let me know.

But anyways each cord will have the round pin 7 pin plug on the end of it.

We will then be making adapters for every style of plug both male and female that will be only the length of the plugs plus a couple inches to allow a little flex if needed. These will all be stored in cubbies below the switch box and labeled to suit. At first we will just make all of the different trailer plugs but may add some weatherpack adapters as well later on.

We will have all of the charts and diagrams laminated and on a ring sitting in a slot between the cubbies and the switch box.

A decent size 12 volt battery will be sitting on the base of the hand truck with a battery tender mounted to it so we can plug it in when not in use.

The reason for the two plugs in the switch box is for incoming power and outgoing power. We want to be able to power up trailers, and also just check the other equipment (semis tractors pickups etc.) And we also would like the ability to quickly check pigtail cords.



Now heres where my basic wiring questions come into play.

We want to be able to have a switch for each wire that will be sending power out. We will be labeling what each switch is powering and we were going to have a light for each switch going out but now I have decided it would be better to add a voltmeter and ammeter so you truly know whats going out which would mean we would not need the lights anymore really.

Now on the power coming in side we would still use lights which would be labeled just like the switches, but i would like to also run them through a volt meter and ammeter.

Furthermore I am sure i will need to have this system wired with circuit breakers as well to protect it, the vehicle, trailer and also help with diagnostics.


Essentially what I am looking for is how to wire everything inside the box. I can do good wiring and make everything but the concepts of it still confuse my brain as i havent really worked to try and understand it too much.

Starting with the power going out side.

Here is what I am thinking, the power goes to the switch to the voltmeter to the ammeter then out through the plug.

Now here is my question, where do I put the circuit breaker in this system? I know i need to protect the lowest rated items but if im thinking correctly i want to be testing the trailer system at its full capacity. The Ammeter should be fine im assuming, i cant seem to find what some of the volt meters are rated for though. And If i use a toggle switch rated higher than the trailer i should be fine there too correct? So then should I be putting the circuit breaker before the switch or just before it goes into the plug? Or do i need it just before the plug and then a fuse between the battery and switch?


Now on the incoming power side, I want to power the light and both gauges. So Should the circuit breaker be the first thing the power goes through?


Now as for the gauges. How do I splice them into each of the 7 wires while still keeping each circuit isolated from each other?



Now for the supplies.

I would like to use digital gauges. Doesnt matter the style or type really just would like digital readouts. Anybody know which ones are good but still affordable?

Circuit breakers? I want ones that are each to reset like the little white push button ones. Am i on the right track or what else should I be doing?


If you can think of anything else im missing let me know.

Thank you much.
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