Date registered: Aug 2009
Vehicle: '72 250C, '74 280C, '85 500SEL, '81 300CD.
Location: Tucson, Az.
Mentioned: 3 Post(s)
Quoted: 72 Post(s)
First place to check is the ground/earth cable. The original earthing point is from the negative battery terminal to a flap on the inner fender. Very common for this area to develop corrosion or even to rust away. Second ground point is from the opposite fender well to the bell housing or starter motor. Also a corrosion point. Don't just look at them. Pull them apart and clean to good metal surfaces.
Next place to check is the positive lead to the starter. Not rare for the solenoid to corrode at the power lead. Not common but if there has been a bad connection for a long time the Bakelite body of the solenoid can separate.
Internal corrosion of the power cables is the next place to check. Look for bulges in the sheathing or corrosion on the exposed cable ends.
I always add a secondary ground cable from the fender well earthing point to the engine block for added insurance.
Remember, voltage is not amperage! Just because you get a 12V reading it doesn't mean you are getting enough current to operate electrical components.
Last edited by Mike D; 02-08-2016 at 02:19 PM.