A lot of early series M37's including mine did not have turn signals. My parts truck (which is a '54) had the mechanical turn signal box installed by the glove box, but the rest of the system was non existant. After checking around a bit, it seemed like the consensus among military vehicle owners was that the original mechanical flasher setup was marginal and could be expensive when you could find the parts while the better solution to use the modern solid state military hardware that was more rubust and much less expensive. It also became pretty apparent that I had erred when I ordered my reproduciton wiring harness in that I had gotten one correct for my vehicle, but in doing so I had not gotten a wiring harness with provisions for turn signals that are included in later series trucks.
That being the case, here's what I did:
I pieced together the parts that I would need for my turn signal instalation while
making the rounds of local MV parts dealers around North Carolina and while ordering other
parts over the internet. I got a set of current composite front lights from Trader
John's Outpost (these are the ones with the amber lens on top with the blackout marker
just below, made of some sort of OD colored plastic. I then got a set of full red
lenses (Gamma Goat - M561) from White Owl Parts for my rear lights (both three bulb units
from the left of the early M37 series, or as used on both sides of the later model trucks)
when I was in Kinston on a business trip. I picked up a turn signal unit (solid
state) while at AB Linn's and purchased a turn signal harness and turn signal switch from
Delk's Surplus on the way back home.
The front composites lights bolt onto the existing market light brackets, I had to enlarge the hole for the wires to pass through as the grommet on the light does not quite line up with the hole in the bracket. I used a hacksaw and made the hole in the bracket into a keyhole shaped cutout.
The rear lenses screwed right on the housings. My housing looked ok on the inside. White Owl Parts had the entire light assemblies (in fact they took my lenses off a pair in order to sell them to me), so my housing had been bad, I could have purchased entire Goat lights for the rear.
The turn signal switch mounted to the steering column with a hose clamp. I put it just below the wheel so I can reach it with my fingers while keeping my hand on the steering wheel. One thing I learned after I painted the interior of the cab after I did my turn signal instalation is that the switch is grounded through the steering column. I had to go back and scape a little paint off the steering colunm to get my ground back...
I ran the harness through the hole above the steering column in the access cover on the dash and then I put the turn signal controller on the bracket located just above the steering column. I had to drill a pair of holes for the mounting screws, and I
drilled another for the ground lead since it's connector was too small to fit on the small bolts I was using to mount the flasher.
I then hooked up the harness that goes between the flasher switch and the flasher unit. Both ends of the harness have Cannon plugs so it was just a matter of lining up the threads and tightening everything up. I used a couple of wire ties to secure the harness to the steering column.
I then pulled apart the harness connector behind the three lever light switch in order to install a lead on pin J, this is the pin that supplies power to the turn signal unit when the lights are on. Some trucks have this pin conected depending on which wiring harness is installed. As I mentioned earlier, I had gotten a reproduction wiring harness without turn signal provisions, so I ended up taking the Cannon connector apart and soldering in a new lead to pin J and then I reasembled the plug and screwed it back onto the light switch.
Using some mil spec wire and a combination of metal and rubber connectors as appropriate I connected up the rest of the pieces. I used the wiring circuit numbers from a table on olive-drab.com, but I had to chase down one mismatched number from what my components are. Pin J on the back of the light switch feeds the flasher through wire marked
461/460 on my harness instead of wire 467 as shown on olive-drab.
The flasher harness wires 460 and 461 go to the front right and left right respectively. The composites have wires with the corresponding circuit numbers. I ended up having blackout, park, and turn signal lights in the front of the truck.
I ran lines from 22-461 and from 22-460 to the rear left and rear right respectively. Since I don't plan on using blackout lights, I just ran the lines at the rear to the 22 wire on each lamp.
For a really "correct" setup, I should run the pin C (circuit 22) on the back of the three lever light switch to circuit 22 on the flasher harness, and then hook the 22-460 and 22-461 back into the correct lines on the truck to maintain the rear blackout lights, but then I wouldn't be able to run the full red lenses.
Since installing the turn signals in the truck, I have converted the truck to 12 volts. The conversion of the turn signals involved swapping out the bulbs and replacing the flasher unit. A description of this is given on the 12 volt Conversion page.
Recently, one of the guys on the MVEmail list created a turn signal page discussing the
workings of the M-Series turn signal switch including a schematic that I found to be a
great reference especially when debugging a system that has stopped working.