click, buzzing, but no start

[camoit]

Many times bad battery cables are the problem. Resistance builds up over the years. Then all the do is act like heaters when you want lots of current from the battery. Let's not forget many people remove the ground from the block to the cab. And that causes problems all over the place.

[SubGothius]

...Let's not forget many people remove the ground from the block to the cab. And that causes problems all over the place.

Or it just breaks or oxidizes away, possibly inside the insulation where you can't see it, or the exhaust manifold stud it's connected to can get rusty over the years making for dodgy continuity. Mine seemed possibly fragile (it's an oddly stiff wire), so as a precaution I supplemented it with a braided ground strap in parallel, connected to the rearmost intake manifold stud instead of the exhaust which looked pretty rusted solid.