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can anyone in readerland explain the thinking on the trailer industry??
Im relaxing the 7 way trailer plug on my car hauler. I thought the way the trailer was wired was kinda screwy the last time I worked on it, this lug makes even less sense.
I bought a 7 way pre made Hopkins plug with LED diagnostic lights. If you follow the wiring diagram included (which happens to follow the function on my Ram) black is battery or Auxiliary power. To the best of my knowledge, every automaker has always used the color black to signify ground. In the trailer industry, white is ground, as is this plug. At least they were thoughtful enough to keep GM color coding for taillights and turn signals.
Im just curious if anyone knows why the trailer/tv industry choose black as power. It defies logic when it comes to basic automotive wiring. At the same time, it seems there is usually a reason for seemingly stupid practices. Just wondering if this is one of those times.
V
can anyone in readerland explain the thinking on the trailer industry??
Im relaxing the 7 way trailer plug on my car hauler. I thought the way the trailer was wired was kinda screwy the last time I worked on it, this lug makes even less sense.
I bought a 7 way pre made Hopkins plug with LED diagnostic lights. If you follow the wiring diagram included (which happens to follow the function on my Ram) black is battery or Auxiliary power. To the best of my knowledge, every automaker has always used the color black to signify ground. In the trailer industry, white is ground, as is this plug. At least they were thoughtful enough to keep GM color coding for taillights and turn signals.
Im just curious if anyone knows why the trailer/tv industry choose black as power. It defies logic when it comes to basic automotive wiring. At the same time, it seems there is usually a reason for seemingly stupid practices. Just wondering if this is one of those times.
just a pure guess, but in AC home current , black is hot and white is neutral, which eventually goes to ground.
By the way, the left hand diagram (yellow left turn, green right turn, brown tail, and blue brake controller) is the GM standard color code. Got no clue where the black/white/purple came from.
I'm w/ Pat. Often you will find trailers which use 5 wires w/in a 7-blade trailer plug if you have no need to run or power equipment (accessories) within a trailer - most utility trailers only require a flat 4-blade trailer plug anyways - there is no requirement for a power source outside of the normal vehicle lighting circuity. Whenever you get to the point where a trailer "requires" use of a black wire as a source of power in a trailer plug, that trailer most often is a self-contained camping trailer, toy-hauler, etc. capable of employing the vehicle's battery as a source of power (e.g. under tow) to supply electricity in varying capacities/capabilities - trailer contains a generator, an inverter &/or a converter - depending on the type and availability of power (DC or AC, you can plug a trailer into a direct AC 30A or 50A power source). In those cases where a black wire is required in the trailer plug, I've found it always follows AC circuity. And, again, there are many types of trailers with no need for a black wire power source in a 7-blade circular trailer plug and that blade is left blank along with one additional blank blade (I think it's a brown wire - but it makes no difference what the other color is), the point is if there's no need from the trailer to employ a black wire power source from the vehicle then the trailer is not wired to receive an external power source to begin with. Does that make sense? I've owned several trailers with 7-blade circular trailer plugs - some wired without a black wire and some wired with a black wire. In all cases, any time a black wire was required in a 7-blade trailer plug that trailer was capable of running off the vehicle's DC power as well as independent of the vehicle in either a DC or an AC configuration, but the wiring of the trailer always followed AC circuity.
Last edited by Vintage Chief; April 6th, 2022 at 06:09 PM.
I've found trailer wiring perplexing sometimes also. It's always an adventure trying to match trailers to tow vehicles, troubles always arise when you borrow/rent a trailer in inclement weather and the wiring is a mismatch.
By the way, if you look at GM courtesy light wiring, the white is always ground.
By the way, the left hand diagram (yellow left turn, green right turn, brown tail, and blue brake controller) is the GM standard color code. Got no clue where the black/white/purple came from.
Yep, I printed off a copy of that exact diagram for my library. Not sure why I bother doing that, since just about everything is available online.
As long as the RV/trailer industry has been around, I’m really surprised this wasn’t standardized years decades ago.
I'm w/ Pat. Often you will find trailers which use 5 wires w/in a 7-blade trailer plug if you have no need to run or power equipment (accessories) within a trailer - most utility trailers only require a flat 4-blade trailer plug anyways - there is no requirement for a power source outside of the normal vehicle lighting circuity. Whenever you get to the point where a trailer "requires" use of a black wire as a source of power in a trailer plug, that trailer most often is a self-contained camping trailer, toy-hauler, etc. capable of employing the vehicle's battery as a source of power (e.g. under tow) to supply electricity in varying capacities/capabilities - trailer contains a generator, an inverter &/or a converter - depending on the type and availability of power (DC or AC, you can plug a trailer into a direct AC 30A or 50A power source). In those cases where a black wire is required in the trailer plug, I've found it always follows AC circuity. And, again, there are many types of trailers with no need for a black wire power source in a 7-blade circular trailer plug and that blade is left blank along with one additional blank blade (I think it's a brown wire - but it makes no difference what the other color is), the point is if there's no need from the trailer to employ a black wire power source from the vehicle then the trailer is not wired to receive an external power source to begin with. Does that make sense? I've owned several trailers with 7-blade circular trailer plugs - some wired without a black wire and some wired with a black wire. In all cases, any time a black wire was required in a 7-blade trailer plug that trailer was capable of running off the vehicle's DC power as well as independent of the vehicle in either a DC or an AC configuration, but the wiring of the trailer always followed AC circuity.
Ok, that actually does make a little sense. As I suspected, there usually is a reason for seemingly stupid things.
The trailer when I first bought it only used 5 of the 7 wires. One of the first things I did was put some junkyard fog lamps on the rear to provide some light when backing up. That required a new trailer plug, since the one on the trailer didn’t include provisions for reverse lamps. Later, when I installed a winch and deep cycle battery to power it, the black “battery” wire was used.
Actually the yellow, green, brown, white is the standard color code for four wire systems for light trailers. The five, six, and seven pin connectors just adopted that and added to it.
April 6th, 2022, 04:03 PM
