Haulmark dual axle in reverse braking

[graygray1960]

Hello
Just hoping you could confirm the colour wire which activates the brake lock out solenoid for reversing on the dual axle trailers.
As far as I can see everything is hooked up and working except the lock out solenoid.
I do have 3 spare wires running to the rear.
2 x blue (Says service brake in the diagram-so a possibility maybe)
1 x purple (Aux-I think)

Cheers

[Mick_Marsh]

It should be hooked up to the brake.
The idea is the solenoid allows the brake fluid to flow when the brakes are applied.

What are you hooking the trailer up to?

[Dervish]

Hello
Just hoping you could confirm the colour wire which activates the brake lock out solenoid for reversing on the dual axle trailers.
As far as I can see everything is hooked up and working except the lock out solenoid.


This again. I can see this is going to be a common question. Your trailer is almost certainly functioning as designed; it just wasn't designed well. As Mick said, the solenoid is normally closed and it opens to let pressure into the brake side of the circuit when the brake lights activate. Unfortunately, there is no means of relieving the pressure if there is residual when the brake lights deactivate, thereby holding the brakes on. It really is a dumb setup, someone dropped the ball in a big way.

At least one person has wired up a relay to deactivate the solenoid even when braking while reversing. That solves some of the problem, not all.

Consider this; you nose down an incline on a 4x4 track or driveway etc. You are forced to stop and reverse up the hill. Well, you're buggered aren't you - reverse mod or no. What the system needs is some kind of one-way valve to relieve pressure on the brake side of the circuit when the solenoid closes.

[graygray1960]

I am hooking up to a 94 200 tdi defender 3 door.

[graygray1960]

Thanks. I will be towing with a 94 200 tdi 3 Door Defender LWB
Cheers

[graygray1960]

Connectingthe solenoid lock out trailer wire to the reverse light wire on the defender makes sense as this would activate the solenoid in reverse when backing up.
But with 2 x blue wires spare could it be one wire for each side for the lockout.

[Mick_Marsh]

Connectingthe solenoid lock out trailer wire to the reverse light wire on the defender makes sense as this would activate the solenoid in reverse when backing up.
No it doesn't as this would allow the fluid to flow and the brakes on the trailer to be applied.
The solenoid is not a lock out. It is an enable.
Hook it up to the brake light. The solenoid will then allow the fluid to flow whenever the brakes are applied.

So, what are you doing? replacing the plug on the trailer, installing a NATO socket on the Defender or making up an adaptor lead?

If you are making up an adaptor lead or replacing the plug on the trailer, what sort of plug will you be using?

[Mick_Marsh]

But with 2 x blue wires spare could it be one wire for each side for the lockout.
Just looked at the wiring diagram for the trailer plug. The two blue wires are the tail lights of the trailer.

[graygray1960]

Thanks very much for your assistance.
The trailer lights are working ok it seems.
I have a small 7 pin plug wired for the trailer having removed the NATO plug.
The trailer Brakes appear to work as expected when going forward and yet are locking on only sometimes when in reverse.
The reverse light is not totally reliable on the dfer. Perhaps this is causing a problem.
Also if I unplug the trailer from the vehicle and reverse it seems ok.
I haven't tried it uphill thou.
Thanks

[graygray1960]

There is another wire attached to the brake wire, this is the solenoid activate you mentioned I expect.
The brakes lock on when reversing up an incline . I guess the pressure on the hydraulics activates them.
Otherwise it appears to reverse ok.
If the brakes lock on in reverse I have noticed that pulling the 7 pin plug out of its connection allows me to back up the incline.
Regards
Graham