Round or Flat trailer plugs?

There is an Australian standard for trailer connections - See This Link - Wire the brakes as per this standard. If you do not then it will be possible for someone to inadvertently couple a trailer with brakes to your vehicle and find out they have no brakes if you wire the brakes through the large pins in a 12 pin plug. Pin 5 is sufficient for four wheel brakes. In addition, if you wire the wire the brakes through the large pins then you can not tow another van that has only a seven pin plug (trailers with seven pin plugs can be connected to the 12 pin trailer sockets on the tug.)

Keep to the standard.

Hi
Use the largest pin and cable possible . All this to prevent volt drop especially on twin axle braking or use a more durable separate connector for brakes .
I have repaired ""just a few "" this way with great reliability and success.

I suggest that members stick to the standards and not to deviate from them. It takes a very sensitive voltmeter to measure any significant voltage drop across the trailer connector pins (unless of course you do not maintain your trailer plug properly.)

How many of you out there have had the trailer brake pin burn out?

Cant say I recall ever seing one melt a brake pin Peter,and I have replaced many dozens over the years. It is almost always the earth pin that melts.

The other big problem is a corroded tail light pin in the cars socket from it having 12 volts on it at night when the socket gets wet, mine it green at the moment too. Used to see pin 2 melt and corrode too but not often connected anymore.

Melted earth pins - If you have a 12 pin connection, make sure pin 10 is well earthed both in the tug and the trailer. Do this even though you may not use the large pins for heavy current. That will assist the small earth pin with current carrying.

That pin 2 problem - I got caught with it before I became aware of the low rating of the small pins. As a communications tech I am well aware of voltage drop problems. When I got my first 3-way fridge (the ones before were only 2 way - no 12 V) I attempted to improve the efficiency of the fridge whilst towing. I replaced the piddling thin manufacturers wire with 6 mm2 wiring in both the van and the tug. On the first long outing, I could not get the plug out. It had welded itself well and truly into the socket. I had to break the pin before I could uncouple. That's when I found out about about the real ratings of the connectors and 12 pin connectors. I have had 12 pin connectors on all vans over the 25 intervening years I have not had a pin burn out.

Many manufacturers have and still do, do not follow the standards. They still thieve pin 2 to power the fridges. They get away with it as the wiring is too light and the reduced voltage at the fridge due to voltage drop does not draw enough current to stress the connector. However, it also means the fridges do not work as designed on 12 V.

Had a run of problems with electric brakes not working very well when the fridges were turned on due to well greased towballs and light earth wiring to the car.
Some of the vans had a chassis voltage as high as 4 volts higher than the cars.

These days with LED trailer lights bad earths are not as easy to spot without the feedback glow from the other light circuits.

The round plugs both large and small have claws arranged in the cover flaps to hold the plug in also but the spring usually corrodes and renders it useless in time.
My preferance is a 7 pin flat but my present one hasnt got a flap, after doing such a marvelous job installing it above the rear step to make it more accessable the bloody flap didnt have room to open far enough to get the plug in so i took the flap off.

So your travelling flapless Q/c. Are you sure that's legal. :)
Dave.

Haa Dave, there is somewhere I am not brave enough to go lol.

If that flap does not lock properly then the plug is likely to work its way out. It will fall to the roadway so he then has to replace it. It will not be long before he has to do something about it.

Theoretically correct Peter, but it is a tight squeeze to get it in where it is and the top of the rear step rests firmly against it so it is a 2 hand operation to remove it, it wont go anywhere on its own.
I had no choice but to put it up there because the old position was not protected by the stone stomper and both it and the anderson plug got destroyed after a couple of days on gravel.
Luckily I had a 6 pin Deutsch plug and receptical in my "might come in handy" box.
The way the electrolysis is setting in to the flat socket I am considering replacing it with Deutsch permanently and keeping it sealed with a senson filled cap. Sort of half way to a military version, just means I will need a couple of adaptors on hand.
All this because my flap has been removed and I can see whats going on before I actually need to use it.

Even the 12 pin variant, which does have large power pins, is sus for power and best an Anderson plug arrangement is used for any significant power transfer to caravan.



The large pins on the 12 pin plug are rated at 35A........double them up and you have 75A. Pretty good compared to the anderson 50A plug.
'
I have 12 pin plugs, but both 4wd and van had andersons, so I have not bothered to use the 12 pin large pins.

Gronk - Anderson SB50 connectors are actually rated to carry 120A. The 50A rating is a UL rating for hot plugging.

See the datasheet: https://docs.rs-online.com/cf13/0900766b81714eef.pdf

I'm not sure how the 35A rating on a 12 pin trailer plug/socket is calculated/measured - it is probably in AS4177.5-2004 but I don't have access to the standard.

Can’t say i’ve had any issues in 10 years of owning our Kimberley Kamper with the large 7 pin round plug it came with, the plug has performed flawlessly over much of Australia and still going fine.

Hardly any caravan manufacturers tow caravans throughout Australia for any period of time so are not good ambassadors for lots of things. In a previous job I rewired trailers of a fleet and replaced/ fitted many many troublesome round 7 pin plugs which fell out or failed because of loose pins. The notion that large pins are better is flawed with the plug only passing electrical flow where the pins actually can touch their mating surface. Pull out a 7 round base or plug and look with a magnifying glass what contact there really is, you will be alarmed. An accurate 7 pin flat system can't be worse. 7pin flat fits into 12 pin base flat/2 row, so is handy if other vehicles are involved.

The reason the manufacturer wouldn't fit a flat one was because they had hundreds of round plug systems in stock and wanted to sell them otherwise they lose on the bulk deal purchase they made.

Wouldn't know about any technical details really, but I do know I had no issues with the Large Round 7, whereas I have always had issues using the flat 7.

Another issue that helped force my hand is the BT50 manufacturer's trailer wiring and the 12 pin flat socket they use. It is a Mazda-branded socket and has two extra wires in it that are connected to a reed switch which is operated by a small magnet in the dust lid. If you listen carefully you can hear the switch operate when you open and close the lid.

The BT50 has trailer sway control. I presume the reed switch tells the vehicle that a trailer is present, probably to turn off reversing sensors where fitted and also, perhaps, to activate trailer sway control. The manual gives no clues that I can find to confirm that. I have asked both my dealer and Mazda customer service about the trailer sway control component but have been unable to get a clear answer.

I took the precautionary approach and left the flat socket in place, in the hope that I get a better run out of it than I did with the large round.

You are right Frank, the lid does contain a magnet and reed switch buried in the Base with two contacts. Isuzu tow bar bases have the same system to switch off reverse sensors when towing. Magnet closes reed with lid closed and the reed switch for camera and sensors and no magnet opens the reed, ie, an "NO" status reed, very small current through that though.

Not sure if the base lid magnet/reed has a bearing on sway control as any damage to the base would render sway inoperative. Pretty non techo is the base of most vehicles. I presume sway control is done by an inbuilt Yaw sensor in the vehicle, similar to Alko caravan sway detection, or rather Alko has used the tech for cvans.

Yep, Utilux alloy large round, problem solved. Never falls apart, large terminals make it easier for breakaway battery feeds or piggy backing wires for extra signal lights. The one on our LC has been around since 1994, still going.

i wish I had such luck with the round.

Now using Utilux Alloy 12 pin flat.

I always use a Lanolin spray into the wires of bases and plugs so the green verdigris and any rust is severely retarded from developing. So a good idea, YES? Also means the screws are lubed to be able to service or replace whenever required. The Lanolin also tend to run water away from the innards of the plug to further assist with prevention.