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If you ever plan on installing any electrical accessories they are the best and cleanest way to pick up four powered circuits. Everything just plugs in and you have 4 relay controlled circuits - 2 fused for 10 amps each and 2 fused for 30 amps each. All circuits are live only with the engine running.
As an example I use one 10 amp circuit for my high idle control and the other for front and rear strobes. One 30 amp circuit is used to control my mirror heaters and the other is a spare at the moment.
Between the upfitter switches and the customer pass thru wiring adding electrical goodies is a snap.
The PSD doesn't like long periods of idling. It develops a condition known as "wet stacking" where unburned fuel accumulates above the exhaust valves since at idle the cylinder temps aren't high enough to burn all the fuel cleanly. What constitutes "long periods of idling" could start a discussion in itself, but my personal feeling is that you shouldn't let a cold engine idle for more than about 10 minutes or a hot engine idle for more than 20 minutes.
There is a wire bundle under the dash that contains a capped wire that when 12 volts is applied to it and the truck is in neutral with the parking brake on the idle will go to about 1200 rpm. That's high idle. It's also handy if you're going to run something electrical that has a high current draw such as an electric winch or a high output inverter. The high idle wire doesn't require much current so one of the 10 amp upfitter switches is just the thing. It's a quick 15 minute mod.
just to give another op on the switches, i spent 90 dollars shipped and they look great, i have already used up 3 of them and are easy to install and hook up to later. deffinately worth the 90 dollars. mine also came with the small cuby hole to keep it looking stock.
On the driver's side. It is four colored wires--believe they all have black end caps & white tags on them with AUX01 - 04 or some such written on them.
There are plenty of other resources out there...you just need to do some searching to find them out!
Incidentally, I have the full install kit (upfitter switches, wiring harness, relay box, small cubby hole) that I have not & will not use. (Bought for my previous Super Duty, but never installed/used them before trading it in.) If you are interested, PM me.