Given the descriptions above, there's no permanent fault code if the solenoid is disconnected, right? Only a temp code while the system is defeated (lost signal from the solenoid), that clears once reconnected?
Since the ESOF t-case still functions even though the relay is disconnected, and the only fault is the "check 4x4 system" light coming on, then do we really need a relay?
Would not a simple SPST switch not work; essentially an on/off function?
Sure - if you are bothered by the little light on the dash, the relay would alleviate this issue by fooling the circuit, when used as described above (first activate ESOF, then drop out relay to disengage hubs)
But if you only intend to use this aftermarket feature very intermittently (essentially for only a minute or two while backing a trailer up for the low-gear advantage, every once in a while), why bother with the relay at all? Just hook up a toggle switch and be done with it.
Using a SPST switch would mean the NC (on) position would be the "normal" 4x4 hub function, and the open (off) position would be 2L. It's just that simple, is it not?
For less cost, easier wiring, and still getting 100% same functional effect, I'll take a switch over a relay every time.

Now - I'll I have to do is find that little bugger on my 6.2L ....

 

dnewton3 - I believe your premise is correct and I don't mean to speak for nuctrooper, but, the upfitter switch is already wired into the engine compartment. I already had a relay "laying" around. It took me longer to round up the tools for the install than the actual install. I mounted my relay to a vacuum hose near the vacuum solenoid using self sealing silicone tape. The only wire I had to "add" was the ground for the relay. easy-peasy and almost free.

 

 

 

The upfitter switches are all on relays though -

 

Yes they are, but the access point to the upfitter relays is the relay output power. It is either 12V(on) or 0V(off, non ground). To do this mod, you need to be able to interrupt power to the vacuum solenoid (or interrupt the ground returning from the vac solenoid - same purpose electrically). That's the purpose of the second relay when using the upfitters to wire this mod - provides that NC contact (87a to 30) that can be powered OPEN to interrupt power to the vacuum solenoid. (If not using the upfitters, no relays are required at all as discussed above)

 

The reason I used a relay was to have the failure mode be "back to stock" (if the relay coil or its wiring or switch fail, you would still have 4WD).

 

OK - I get the intent from the OP now. Being that he had an available UF switch, he has to "power" a relay to "disconnect" a circuit. Essentially he's having to power a circuit to drop another. That being the case, he needs the aftermarket NC relay to achieve this.

My truck does not have UF switches. I think I'll just put a SPST switch in to interrupt the activation signal and have the "simple" solution. "ON" for normal ops and "OFF" for 2L operation.

Thanks all!

 

The 6.2 switch is right next to coolant overflow tank, you will see 2 vaccum lines attached, simply unplug first, if your in doubt ( put in 4low and try steering )

Also - the purpose of a relay is to avoid any voltage drop. The high current draw flows from power > device, and not via a switch.

 

YUP - found the solenoid last night. It's in the same spot, but oriented slightly differently (rotated on it's axis for some reason). The solenoid is on the coolant res, clipped up high and on the side facing the cab, closer to the fan. Pretty much like the 6.7L set-up, but appears a bit different. Mine also seems to have more distance between the solenoid and check valve, as opposed to the OPs set up.

I"m curious how much amperage runs through this device? Has a fairly substantial gauge wire running to it. That little solenoid probably isn't consuming all that much power; wonder if other things are in series with it that would be causing a higher amp draw?

 

Just to update ...

I did get around to installing my switch/wiring to isolate the solenoid. A few notes here:
Despite the wiring that goes into the solenoid connector being fairly thick (maybe AWG14 or larger?), the circuit itself does not need anything that large. I had presumed that the circuit was fairly high in amp draw based on the size of wire that goes directly to the connector that attaches to the QD fitting on the solenoid. That made me make sure to buy some 14ga wire and a 20amp rated switch. But when I peeled back the wiring loom cover, I discovered that the connector has spliced joints on both sides of the connector; the wire gage steps WAY DOWN, maybe as small as 22 ga once inside the wiring loom about 5 inches back from the connector. So, there's really no reason to buy thick wire or a heavy-duty switch if you're going to install a simple switch like I did. Had I known, I would have got a smaller switch and thinner wire (maybe 18ga) and saved some money as well as made the wiring a bit simpler to install. I had to run a separate loom cover over the pair of wires I installed once spliced, but could have probably shoved a thinner set of wires into the existing harness cover, by splicing the wires into the thinner gage stuff just a couple inches further back from the switch. Simply put, a 3amp rated switch and some 18ga wire would do just fine.

 

Good info, thanks.

 

Yeah, this is gonna get done ASAP on my truck, as I use low gear often when camping because we tend to camp in places where everything is tight, and the movements are small. 4 low is fine, but it cuts into turning radius.

 

What are the pros or cons of switching the solenoid ground wire vs hot wire with the new relay. It looks like Nuctrooper choose to open the Ground to the vacuum solenoid opposed to opening the Hot wire to the solenoid. I understand either would work, but what is the logic to choosing the ground vs the hot?

 

Should make no difference whatsoever. All you are doing is interrupting a circuit, doesn't make a difference weather you do it before the solenoid or after.