easily accessible +12v power source under the hood?

[Vetruck]

The 12v to the blower. Drivers side fender. You'll see two or three black wires that meet under a little plastic flap. Direct 12v to battery there.

Thank you. Yes I in fact borrowed a multimeter from my neighbor yesterday and verified this exact thing. I figured that little covered box with about 8gauge wires would be my all time hot lead since the battery is in the trunk, That makes things very easy to pull a switched lead from the fuse box AND a hot lead from this little box right in front of the fuse box. It will make for a clean install right into the same covered loom(I hate nothing worse then exposed wires in an engine bay).

The controller I am looking at is one of two. I am heavily leaning towards the "Painless Wiring" F5 pulse width box that will run the fan on variable speed-as the temp increases the fan rpms increase. Derale also makes a PWM module, but the painless unit also has a start delay feature and a timed shutoff run to cool just about 30 secs more after shutdown of the ignition.

I have to still measure things exact by pulling the shroud, but preliminary measuring looks like I can squeeze this Spal 16" fan directly mounted through the radiator and use their fan gasket kit to seal it against for very good puller flow without a shroud. It is rated at 2036 cfm @ 19 amps draw- and is a curved blade design to reduce noise. Those little two OEM assist fans up front are noisier than hell.
http://www.a1electric.com/Merchant2/..._Code=30102049

A little side note- I have run dual electric fans on my truck motor for about 15 tears now, as well as an electric waterpump (which people told me years ago I could not do- this is my daily work vehicle and runs a 55GPH Meziere electric pump and dual 13" cooling fans on a BeCool 4 core racing radiator. The truck puts out 385HP and is used to haul heavy loads of construction material often- it never breaches 172". The only problem I have had with this system is it dithers on and off because there is no dwell time on between the one temp and off temp. It cycles on and off all the time and spikes the amperage- which I can visually see the digital Dakota dash gauges change every time this spikes. (Thus the desire to run a variable speed unit on the Mercedes so it only slows and speeds up- thus no amperage spike from constant on/offs.

THis 1)saves on gas mileage, 2) less pressure on the water pump shaft holding the clutch fan setup (waterpump will last forever), 3) quicker warm ups to operating temp on a cold morning (fan stays off until coolant gets warm/hot), and 4) more power to the wheel of course since the motor does not have to spin the power robbing mechanical fan assembly.