I have a 1984 W150 and it has a cranking issue. When I first got it a couple months ago, it cranked just fine. Then I noticed that it would crank for a few to several seconds (usually long enough for it to eventually start), but then quit cranking. I could turn the key to the off position, and turn it back to start and it would crank again. Now, it cranks very briefly before I hear and feel a click through the key and it quits cranking. I turn it off and crank it again...brief crank then quits. The click through the key seems to be interrupting voltage to the starter. Any ideas?