Trailer wiring help

[Stevo78]

Just a simple question for someone on the forum to answer... for me, not so much.

Long story short, I was going to replace my 7-pin on my 74 sovereign, easy right? For me, not so much apparently. After googling and forum hunting I found the connection point and came to the realization that I don't have to replace my 7-pin, I just have to find out where this wire is normally connected. I think it's a ground wire.... I think. The picture below you can see the wire in question.

Could someone please tell me where the wire is supposed to be connected?

Please excuse the butcher job on the skin.

[Joyflea]

May help . Blue

[uncle_bob]

Hi

On any older trailer it's very much "trust but verify". If you think it's a ground wire, grab a multimeter and see if it shows zero ohms to ground. If so, you got it right. If not, guess again .....

Bob

[Stevo78]

That's the best diagram I have seen to this point. Thank you both for the quick reply. I'll be testing when I get home

[Atomic_13]

The diagram makes sense to me with exception of connecting the converter to the 7 conductor black wire. Why is this necessary?

Note the diagram already has the black wire connected to the battery (for the trailer brake power via the trailer switch if a trailer would uncouple while towing).

Also, the converter would only supply power when the trailer was connected to 110v via the campsite or a generator.

[Atomic_13]

One additional question I’ve also has about the 7 conductor wire. Do all wires need fused or only the black wire?

[Belegedhel]

The first thing to be aware of is that the wire colors in your '74 very likely do not match modern conventions, and if your 7-pin is wired as it originally was, then it is not compatible with modern norms either.

So, if you have been towing your trailer, and the lights all worked fine, then someone probably already rewired the 7-pin to be compatible with modern conventions (or your whip is wired to serve as an adapter). If you have never had the lights working, then you are going to have to figure out where each of those wires goes, and then confirm whether they are wired correctly to the 7-pin or not.

On my '73, the white wire was a ground. See the attached diagram for a modern wiring of the 7-pin. Also attached is the wiring diagram for my '73.

As to what is fused, the only line mine originally had fused was the blue charge line.

good luck!

[uncle_bob]

Originally Posted by Atomic_13

One additional question I’ve also has about the 7 conductor wire. Do all wires need fused or only the black wire?

Hi

Fuses protect wiring at the source of power. They need to go up close to the battery or panel to do their job correctly. If they are a ways away from the power source, some of the wire is unprotected. It can short out and cause a fire.

The lines to the 7 pin connector all should be fused in the truck. That works fine for the lights and brakes. The gotcha is the charge line. It (at least potentially) has a battery (power source) on both ends. Thus it needs to be fused in the truck and fused in the trailer. Yes, that's weird.

Ground (and neutral if it's AC) lines should never get fused or switched. They should just run back to the panel or battery. On AC wiring people are pretty good about this. On DC stuff ... maybe not so much ....

Bob

[Atomic_13]

N/a

[Atomic_13]

Thanks, Bob. That makes a lot of sense.

What’s your thoughts about the diagram posted by Joyflea. Any reason why the illustrator proposes connecting both the battery and converter to the black power wire? I want to make sure I’m not missing something. Seems to me it should only need connected to the positive buss of the dc system or perhaps as a fused circuit off the 12 distribution panel. Agree?

[uncle_bob]

Hi

The stock AS setup in many trailers is to have a DC bus in the front of the trailer. The battery tags into the bus via a self reset breaker. The charge line tags into the bus via s similar breaker. Various other bits and pieces fan in or out of this busbar via the same sort of breakers. Mostly it is things like the brakes and various "power" accessories.

What ever you do, there should be a fuse or breaker in the charge line from the truck. That should go as close to the trailer battery as practical.

I *hope* that makes sense ....

Bob