Slick 60's

I just bought a L750 dump truck for my son. I looks like it has the 391 and a 5-2 trans. It's a 74 and seems to be a very solid old truck. It's not a slick but you guys are a great resource so I thought I would see if you could help.
I need a wiring diagram and an air diagram. The headlights were a little unreliable when we brought it home.
Any resources that you guys may know of would be great.
Thanks
Jeff

I am away from home right now and will not be back home until early October. If you still need info when I get back I have both air and wiring diagrams for the L series Ford trucks.

Thanks Michelle I appreciate any help you can provide. I would Ebay something but the sellers don't seem to know the difference between a delivery van and a long haul truck.
I have another truck question.
It has 10.00-20 rubber all the way around. The rear duals have a scuffed appearance on the tread like someone has been out smoking the tires. I don't think the 391 is up to the task so that makes me wonder if I have an alignment issue at the rear end. We put three hours on it at highway speeds and the tires had the same appearance.
It is all over the road. Is it possible for the front to work the back hard enough to scuff the tread?
I haven't jacked the front end up yet to see what is loose.
Jeff

Is the truck a tandem? If it is, the tandems will scuff some when turning corners but shouldn't be to bad. If it is a single axle make sure the spider gears are not locked up. You can also check the interaxle differential switch to see if it is engaged if the truck has tandem axles, that will make it scuff. If none of the above applies I would start checking alignment from front to rear.

Single axle dump truck. L750 24000 lb gvw 148" WB
I hadn't thought about the rear end being locked up. I'll put it on the list to check.
I've heard good things about the Ford frames and it didn't show any signs of stress.
But it is a dump truck so it has likely looked like a pretzel once or twice in it's life.

Let me know what you find out.