1967 M35A2 Lighting problems

[Lenny]

I haven't run my truck all winter. I would hate to subject it to all the salt they use on the roads here in New Hampshire. However it started right up the other day and it runs fine, however I found that in both front light units (that hold turn signal, black out, and marker lamps) the marker lights, (circuit 491on the schematic) on both left and right sides do not work. I found that the O rings on both lights were flat and both had leaked. On both of the lamp assemblies The bulbs were corroded in the sockets and I had to spray the sockets with Liquid Wrench and twist the glass part of the bulb out of it's brass base, ruining it to get them out. I did manage to save two bulbs but all the others were lost. I tried new bulbs in the sockets after I polished the sockets with a Dremel tool but the circuit is dead. The diagram shows that wire 491 leaves the light switch on terminal L and first feeds the drivers side marker and then it jumps over to the passenger side where it feeds the other one. This problem suggests that the circuit is open somewhere between the drivers side marker light and the switch. So starting at the switch would be my plan, however the switch is in such a tight spot I was wondering if anyone knows of any other common problems that may apply in my situation. Before i rip out the switch (which may also open unknown numbers of cans of worms) if there is a shortcut out here i sure would like to explore it.
Thanks for any assistance, Lenny

 

[Evil Dr. Porkchop]

Just to clarify, you have the 3 lever switch in the “park” position? That’s the only time the front marker lights will be on, they don’t come on with the headlights (but it’s not difficult to make them work like that).

 

[oboyjohn]

Check your grounds for the marker light circuits. There should be star washers there to help complete the ground (at least there are on our Canadian Deuces).

 

[Lenny]

Thanks guys for the suggestions. Just to be sure I just went outside to verify my problem and what you said Oboyjohn. I found that just putting the left hand switch in "Park" doesn't do it, however if the left hand switch is in park and the top switch is in "Service drive" then the headlights are off and those marker lights do come on. I had forgotten about all those crazy switch positions. My M37 doesn't have signals but I confirmed that the marker lights do in fact work the same way. So the good news is it looks like I never had a problem, (other than "operator head space"

I thought that I would be out there troubleshooting a horror show all afternoon. I was so grateful I told my wife. Now I have a whole bunch of other stuff to do....Best regards, Lenny

 

[oboyjohn]

Hi Lenny, Try putting the lower left arm in the panel bright or panel low position. When you want head lights, markers, brake, and flashers, all you need to do is move the top arm to the right to service drive. Everything should work for you. Enjoy!