Rare or Odd? 66 C30 Dually Q's

[Americanrider]

I happened into a '66 C30 that began life as a factory Motor Home, from what I can see of the option sheet (still stuck into the seat back springs but way to brittle to remove) it has Power-ram steering, Power brakes, 4sp SM420 w/ trans brake, front sway-bar, 4 core Rad and rear dually axle w/ overloads.

The camper part was removed years back and set up with a PTO driven Flat Bed dump. The truck was a wood hauler until the PO removed the 327, it sat for 5 years and then he gave it to me. She's rusty/crusty and shows 72K original miles which I think is correct. I'm planning to part out the ol' girl this next summer and it's raining to hard for photos.
No, nothing is for sale at this time please don't ask.

The odd things I noticed yesterday was when I shined a flash light behind the dash I found two red round warning lights, one to each side along the lower level of the dash gage cluster.

The one on the left says:

OVER
SPEED

the right side says:

TANDM
LOCK

This is only the second truck of this vintage I have owned, the other being a '62 1/2ton long step way back in the 80's. Can anyone tell me if these trucks came with a such a thing as a "SPEEDWARNING dash" or something like the 67-72's had? What about the Tandem lock? The rear axle looks like a plain ol Eaton HO72 to me. I cant find any extra wires/cables running to it that would active a locker or make a dash light come on. Can anyone explain these features?