Nissan Patrol 4x4 (Africa)

I'm trying to get my head around a diff lock gremlin

Top solenoid has vacuum. Bottom solenoid has not. (Common issue)
Top solenoid wire gets voltage when diff lock switched off. Bottom solenoid wire does NOT get voltage when diff lock switched on.
Dismantled the dash switch and it is functioning. There isn't much in the plug to fail

So then it would appear there is a malfunction between the switch and the bottom solenoid
From the sketch posted elsewhere on this site it seems the circuit goes from the switch via the ECU to the solenoids.

What other gremlin in the system could be telling the ECU to not give me voltage at the solenoid plug?
The neutral dash light comes on so I assume that switch works.
4x4 light comes on so that switch appears to work
When switching the diff lock switch to On, the diff lock light sometimes has tiny glimpse of a flicker but most times no light at all.
ABS light comes on fleetingly like normal
There is what looks like an LED with a boot over it inside the diff lock switch. That does not illuminate

Apparently there is a "controller" of some sort in the Y61. Mounted under the dash somewhere.

Speak to Graham, I know he has fiddled with this before.

Thanks.

I found the controller and gave the plug a bit of a clean with contact cleaner/lubricator. No difference.
I then re-routed power from the "off solenoid" to the "on solenoid". No response from the "on solenoid". So it seems I have more than one problem, power supply and stuck solinoid

Then I noticed that the whole dash was dead. After I got my mild panic under control I discovered a fuse had blown. Fuse labelled "meter". Not entirely sure at what point the fuse blew

I think I must put this back on my procrastination list till I can think of more ideas before proceeding again. I don't want to fry electronics
I'm from the pre-difflock period in history so can survive without it while I gather my thoughts and figure out my next move

When you guys switch on your diff lock does a light glow inside your switch, just behind the difflock label on the switch? I'm just wondering if that blob in there is actually a covered LED or maybe a fusible link of some sort. There is no continuity through it hence thinking it might be a covered LED

I had a brain wave during the night. I'm not going to sukkel with electronic fault finding. Going to get an on/on toggle switch and run power to the solenoids independent of the vehicles wiring loom to bypass the electronics. That way the OEM diff lock should work same as if I fitted an aftermarket diff lock.

Keep us updated pls.

I was actually going to recommend just by-passing the control unit, effectively making the unit operate like a GQ's locker, and effectively exactly what you are proposing now.

However, then I realized that one of the more important duties of the controller is to de-activate the ABS.
That's when I decided to shut up, because I don't know if the ABS trying to activate while the locker is engaged can cause damage somewhere...

Hmm..... good point.
I must figure how to check if my ABS actually works because when my front axle was refurbished Dennis pointed out that the sensors looked quite vrot. I don't feel any juddering when braking heavily.

U had same problem on 4.8. Vacuum in off but no on vacuum. Got stuck in a procarios possition with no help. Brainwave hit me. Reverse the lines. Loosened the clamps and reversed the pipes. Difflock worked. I drove off obstacle and immediately switched back. Cannot remember if any lights etc came on though. Changed back immediately because was not sure if abs etc would be disabled as it should.

Untill i sold my troll i could not figure out a fix. Interrested in your final fix.

The system is intricate and has built in safety features..:

It works like this

In 2 wheel drive
- ABS is on
- Diff Lock is off
- Switch lock on - it wont lock, BUT ABS will switch off

In 4 Wheeel drive
- ABS is on
- Diff lock is off
- Switch lock on - Diff Lock will engage AND Switch of ABS
- Disengage 4 Wheel drive, diff lock will switch off and disengage.....

The above is made possible by the control unit and detection of continuity etc through the system

So
If you fiddle and create all sorts of bypass circuits me say you are looking for trouble, rather get to a proper Auto Electrician to fix.