I have a 1995 S10, 4x4. I replaced the vacuum switch with the newer version that has a solenoid. One reason I did this was to avoid a bad vacuum switch allowing transmission fluid to be drawn up into the vacuum lines.


Rather than use a toggle switch to activate it, I would rather find a way to wire it in to work automatically like they do in newer trucks.

Does anyone know where the solenoids in newer trucks get their power? Are the TCCMs different in newer trucks?

Thanks.

 

The TCCM powers the solenoid directly on the newer trucks equipped with the NV236 transfer case.

You will most likely have to pull off of the wiring to the indicator lights in the switch to get power to the solenoid when in 4HI & 4LO (two separate wires). The TCCM grounds the lights in the dash switch with +12V being provided by the 'Gauges' fuse (at least it does in the newer NP233 trucks). To make this signal useful for your purposes, you will need to use diodes to limit current flow to keep the added wiring from lighting up both lights at the same time. You will also need a relay to switch the power to the solenoid to keep the load impact through the TCCM at a minimum. The diodes will be in the ground side of the relay trigger circuit and you'll need to pay attention to which way they go so that they do not back feed & turn on the other light.


In my opinion, you are adding more things to fail into the equation. But you won't get transmission/t-case fluid into the vacuum system... If it were me, I would just check things every once in a while to make sure that the original mechanical vacuum switch wasn't leaking.

 

^^^+1

Or, install the mechanical cable method some have done to lock in the front axle...then I would look into the possibility of modifying the vacuum lines and switch so there is no longer vacuum going to the TC (to prevent the fluid being sucked up into the lines).

 

Voltage comes from the TCCM, and yes, they are different, and not interchangeable. Might be worth looking for an electrical switch with the same "business" end as the vacuum switch that goes into the transfer case. Possibly at Grainger Industrial Supply - MRO Supplies, MRO Equipment, Tools & Solutions. The switch would need to be a normally open, spring loaded, momentary, SPST switch. You will be a hero if you find one!

 

A toggle switch is sounding better and better!

The reason I went this route is that I couldn't get under the truck, due to a lot of snow on the ground for about a month. Believe it or not, right now I am using an alligator clip that I clip onto the battery's positive terminal when I need 4WD.

Thanks for the help. I may try to get under there and check things out, if we don't get the snow they are predicting. Single digit temperatures and a upper respiratory infection aren't helping, though.

 

While looking under my dash for a place to drill through the firewall, I found a toggle switch and a small push button switch under there. Tracing the wires back and doing some searching online, I discovered that it has a remote starter system installed. One wire to the toggle switch already goes through the firewall, so it will be easy to rewire it for the front axle actuator. I removed the remote starter stuff.