I've got a '76 W100 318 that will not start. The truck drove a few months ago and then all of a sudden when i hit the ignition button it didn't do anything. The starter refused to turn the flywheel so i replaced that, didn't work so i replaced the starter relay, didn't work so i had the battery tested, all good, full charge.
Brand new starter, relay, battery, ignition coil, distributor, and ballast resistors, but when i try to start the starter simply makes a single "thunk" sound and thats it. Even when i short out the terminals on the starter with a screwdriver it does the same things, "thunk" and no turning. Right now its a very expensive lawn ornament and i don't know much about the electrical systems in older vehicles.

If this questions has been ask/answered in the past then i apologise for double posting.

 

crazy question, but have you traced aaaaaaaall the wires to make sure they are good and tight? any fuzzy stuff up by the battery terminals? sounds like a loose or corroded connection to me.

 

I've been trying to trace wires but the previous mechanic seemed to like spending money on electrical tape. There are groups of wires taped together that do not need tape, even a wire i found not connected at either end. The battery terminals are squeaky clean, brand new battery and terminals.The lights and wipers work fine when connected, just the starter not rolling.

 

hmmm may be best to bench test the starter then, to be sure. these issues can be a bear but there's only so many things that can be wrong, so hang in there!

 

Put a Socket and a Breaker bar on the front crankshaft nut and see if you can turn the engine over?

 

lol good ole hog, with great advice. yeah. no use trying to trace a starter issue if the engine is seized. good call, man.