1989 Mercedes-Benz S-Class won’t start

I have a 89 420 SEL fan belt broke on the ALT , I replaced the belt but now It will not start, no power at all , I replace the battery. Still nothing HELP.

Given the small amount of info you’ve posted, the only suggestion I can give you is that the belt knocked a wire off when it failed. Look for a rather large wire hanging loose near the alternator.

I had a similar problem (wouldn’t start) with a 1990 560SEC. Had it towed to dealer who couldn’t reproduce the problem. The second time it happened, had it towed to dealer and asked that he keep it and drive it until it happens. Finally found that it had a faulty crankshaft sensor. Replaced that and no more problem. I assume that towing the car disturbed the crankshaft enough to make the sensor work.

Explain what you mean by “will not start”. Doesn’t crank, that rr rr rrr sound with the key in"start"? Or cranks ok, but doesn’t catch and run?

you were driving. belt broke. you stopped? motor did not stall? so we can assume battery was ok. but why did you have to change the battery? were you driving it with broken belt for a bit? that seems odd. i have no idea what the belt arraignment is on a 89 merc. multiple belts? wp is driven by 1? does alt belt drive any other component? like ps? it is 30 yrs old. so i figure it may have had an old battery? new batteries are good.

This vehicle definitely uses multiple v-belts