Here's a pretty good write up that includes the differences between the 1200 rpm high idle, and the battery charge protect high idle.
6.0 High Idle Mod
This is a piece from the link describing the differences between the 1200 rpm high idle and the battery charge protect high idle.
SEIC or BCP wire?
You can hook the switch to either of these wires to achieve high idle. However, they each have slightly different behaviors. If you're doing this mod to help keep the AC cold or the heater hot, or keep the revs up when jumpstarting somebody, then you probably want to use the BCP (Battery Charge Protect) wire. If you're doing this mod to use the PTO (Power Take-Off on your tranny), then you probably want to use the SEIC (Stationary Elevated Idle Control) wire.
If you want to hook up to the BCP wire, find the purple wire with the light green stripe in the bundle just near the top of the emergency brake pedal. Note: don't be fooled into using the light green wire the the purple stripe. That's the output wire for a BCP indicator lamp.
If you want to hook up to the PTO wire, find the solid orange wire in that same bundle (near the e-brake).
Differences in behavior:
BCP
- will automatically vary RPMS from 1200 up to 2400 to maintain battery charge
- does not lock the torque converter
- has an additional wire that is an output that can be used to turn on an indicator lamp to show that BCP is active. I.e. if you want to install an LED in your dash to tell you BCP is on. Since the upfitter switch has a light on the end of this, I don't see much point in this (if you're using a factory upfitter switch).
SEIC
- does not automatically vary the RPMs. Sets idle at 1200 (unless you take advantage of the additional control wire).
- has an additional control wire that you can hook a resistor to to vary the RPMs. You could install a variable potentiometer (i.e. a knob on your dash) to let you dial in whatever RPMs you want, when SEIC is active - from 1200 to 2400 (I think that's the max).
- locks the torque converter.