I am always blown away by the depth and breadth of Shorpy readers' ( Shorpy-ites?) knowledge of antique vehicles and machinery. Model numbers, obscure manufacturer names, details about the internal mechanics, comparisons to similar models from that time -- you guys know it all!
Thanks for sharing all that info.

I think Phare Pleigh is probably right that the wiper is air operated. It looks like the pneumatic king pin release found on many tractors today. Since the truck has air brakes it makes sense to use that system for other things.
Also if the engine is a diesel there would be no vacuum.

On the other hand, most trucks back then were still powered by gas engines. Even the Sherman tanks operating around the world at the time were gas powered. So it could be vacuum.

Back in the mid-70's I used to work on and drive a late-30's White. It was not very far removed from the truck in this picture. Except it didn't have pneumatics, but instead it was fully vacuum. You haven't lived driving a truck until you have driven with Vacuum/Mechanical brakes! The last daily driver I had with Vacuum wipers was a 1972 AMC Matador. Today my wife's 1962 Mercury Comet has vacuum wipers, so we occasionally still get the thrill of climbing a hill in the rain!

The cloth tape was known as Friction Tape, and was used on everything from electrical repairs to wrapping baseball bats.

This is a terrific photo of things seldom seen anymore. But, the spotlight's taped wires may only be where the pigtail from the manufacturer joined with wires brought up from the ignition switch or other source of power. I still have a couple of rolls of friction tape and use the stuff now and then where some heat is involved. Not as good as it gets, but serviceable.

The proper name of the old-style sticky black fabric tape is "friction tape". It is still available. (Ref: 3M 1755)

It's used as a protective overwrap to protect wire from sharp edges.

That spotlight must have gotten a lot of use for it to need repair with electrical tape. The tape looks like the old kind made of sticky black fabric (not the plastic kind used today). Spotlights were more common back in those days--even on cars. My Dad had one on the Nash Ambassador that he bought shortly after the end of WWII.

So says the sticker partly visible on the left side of the dashboard. Once commonly displayed on Texaco service stations, it's seldom seen these days.

http://www.brandlandusa.com/2010/01/23/marfak-lubrication/

Like the previous entry by Mr. Vachon, this photo has a very noir-ish atmosphere to it. Both photos chronicling the work of wartime truck drivers remind me of films like "They Drive by Night" and "Thieves' Highway". The FSA-OWI photographers really knew how to use shadow to great effect in their pictures.

Is that cylindrical thing above the windshield a vacuum-power windshield wiper actuator?

I hated the way the old vacuum wipers would slow or even stop when you opened the throttle wide. This would of course happen when you were accelerating to pass another vehicle, the exact moment when you need clear vision !

Another comment is that in those days, there were no seatbelts. That wiper motor could be a real problem if his head smacked into it in an accident!

His engine is warm and he has 60 lbs of air but his Mack's speedometer is at zero and it looks like he doesn't have any oil pressure and the battery is slightly discharging.

[Not to mention the door is wide open. -Dave]

That windshield wiper motor looks a lot like the pneumatically-operated "Air Push" devices found on locomotives.