Since putting the 06 axles into my truck, I figured I might as well make the vacuum hublocks work. The harley rims have center caps which cover the manual knob, making it difficult to use the manual locking hubs.
Sooooo, challenge accepted
Since I had a donor truck for everything, I had a 4x4 control module, as well as the dash switch for the ESOF and the transfer case. Now the backwards engineering came. I tried wiring up what I could as listed in the wiring diagrams from the service manual, and...... nothing worked at all. That foiled using the 4x4 control module.
No matter what, I needed to use the Pulse Vacuum Hublock Solenoid (PVH Solenoid). This is a regulating vacuum switch, and it is the ONLY way to easily engage and disengage the hubs.
Here is the wiring diagram for it.
After reading countless websites trying to figure out how the vacuum portion works, I finally found one for a Ranger that made the most sense, and it was a very simple explanation. ( I wish I could remember where I found it now).
Basically, the vacuum hub operates like a ball point pen. Apply vacuum, hub locks, apply vacuum again, hub unlocks. The amount of vacuum is different for lock and unlock, which is why there are two different leads for 4x4 and 4x2 on the PVH solenoid. This is why the PVH solenoid must be used.
From what I tested with the truck on blocks, when you ground the 4x2 circuit, 8in/hg is applied to the hubs. When you ground the 4x4 circuit, nothing happens. To get the 4x4 to engage, you have to ground the 4x2 and the 4x4 circuit. This then applies 25 in/hg to the hubs. The manual states that the 4x4 control module applies vacuum for 45 seconds for 4x4, and only 15 seconds to go back to 4x2. With the truck on blocks, I tested and only needed 15 seconds both ways, which made it easier for wiring up a timing circuit.
There are a few wrinkles to the operation of the hublocks that I had to learn on my own. Since its operation is similar to a ball point pen, you have to either remember what state you were in last. The 4x4 control module I think would keep track, but now it needs to be mentally kept track of. Even if you apply the 4x2 vacuum if the hubs are not locked, the hubs will attempt to lock, and sometimes, they will. Sometimes they dont lock, but since there is a possiblility of them locking, there must be provisions made to make sure that the only time you are attempting to lock or unlock the hubs, you know what state you are currently in.
The other design consideration is that the only indication the 96 gives that you are in 4x4 is the light on the dash. Conversley, the only indication that you have that you are not in 4x4 is that the light is out. There is no status from the transfer case to indicate that you are in 4x2, 4x4, neutral, or 4x4 low. This also does not help the fact that if you are going to use the 4x4 light to lock the hubs, they will unlock when you are going from 4x4 to neutral, then they will relock when going from neutral to 4x4 low.
To avoid having a ton of controls and safeguards and having to design some kind of PLC logic to control hubs, I opted for a manual/automatic control of the PVH solenoid.
This was the simplest version I could come up with
The hubs will not lock or unlock unless the trigger switch is pushed. The transfer case has to be in 4x4 or 4x4 low for the PVH to apply high vacuum.
This also allows me to shift the transfer case into 4x4 low and not lock the hubs, to help in moving trailers around the yard into tight places.
I have tested the circuit with the truck on blocks, and everything works. I still have to install it into the truck and make it pretty and integrate it into the dash.