I can't speak directly to a 1937 truck...

but by 1941 they were mounted towards the front of the inside of the inner fender panel.

I'd have to look again, but I think the main wiring harness went up the left side of the engine compartment to the left block, then a second short harness crossed over to the right block.

And the wires to the headlights of course ran from each block to the corresponding light.

So, have a look there.

The Mater Parts Manual calls it “Block, Headlamp wire junction” Group number 2.560.  I believe a 1/2 ton, 1937 pickup is a Series GC.  According to the manual, the block rivets to the radiator shell but it is not listed for a use in a Series GC.

Hope it helps,  Mike 

Terminal blocks were not used on any Chevy until the change to sealed beam headlamps. On previous models with bulb style lamps, the main harness has a three contact, round plug with side pins, that twists into each headlamp.

Mike

Like Ole, I can't speak for the 37 truck but the 38 car is below. IF the truck had them, they would likely be similar.

Here's a comment from Lou MacMillan:

The commercial vehicles had a round plug with 3 contacts for High,    
Low and parking light.   My parts book shows the passenger junction box   
but not commercial. 

@tiny @rustoholic @michael-falise @ole-olson @ole-olson I should have qualified my comments in my earlier post. I have experience with cars through 1936 and trucks through 1939. All of these have the headlamp wiring as part of the main harness and use the aforementioned 3-contact plug.

Mike

Thanks 35Mike, that's exactly the answer I was looking for. You're the man!

Makes a lot of sense, I couldn't find anything on the internet.

Is there some kind of quick disconnect if someone wanted to remove the entire front clip? Or are you supposed to remove the glass and get behind the reflector and just unplug it there? 

Going to be wiring my entire truck really soon so I'm trying to make sure I have everything. 

If your truck has the correct, bulb type, (not sealed beam) headlamps, there is a socket in the bucket , near the mounting bolt, where the harness plugs in. There is a small 3-wire harness inside the bucket that connects the socket to the headlamp and park lamp bulbs.

Mike