If I remember correctly, there are two boxes mounted above the clutch/brake hanger in 77. I am going to try and paint the 40 this Sunday so I'll be in the driveway all day. Swing by and you can steal anything you want off the 40 as long as it all goes back before Moab. If you end up with the working signals and my truck has the problem after the fix...well....then....I'll know
I do have the 71 and the 73 parts available as well but I'm not sure if they are the same.