R500 W251 won't turn over
 

My R500 cranked over very low battery, tried a couple of time than wouldn't turn over at all.
Jump started to another vehicle with good battery still won't turn over.
Scanned with DS708 scan tool which showed a key fault. Reset codes and charged battery.
Has power i.e. all dash lights illuminate and other functions work, turn key to start position and nothing ,no clicks nothing?
Thought must be a fuse but cannot identify?
Any suggestions?

Did you get to the bottom of this at all? EIS maybe?

No, not a dicky bird yet.
I guess the ECM is goosed but again I cannot locate it and nobody seems to know where it located.
As its a V8 engine its not on the engine.
have looked under both floor wells.

If it's the M273 engine (5.5 lt) then it sits on top of the engine as in the photo here. It's silver with fins.
https://cimg7.ibsrv.net/gimg/www.mbw...245eda1822.jpg


I'd be checking the ground wire to the starter (i think it grounds to the chassis close to the catalytic converter). They can corrode at that point which buggers the circuit. These cars are getting older and theses sorts of issues are common. I'd also be retesting yout battery under load witu a proper load tester, not just a voltage test. That could well be your problem.

Also I assume there are no EIS codes showing up? I'd be looking there if you don't get any action from the starter.

It's the 5.0 litre engine and nothing on top of the engine. Really baffling.
The wiring loom from the engine goes to a junction box then disappears into the car so I checked under the left side foot well and dash no luck.

BlackML550 is onto something. It’s pretty common on the 251/164 chassis for the battery cables to corrode. Move the passengers seat up and forward all the way to access the battery compartment. You should be able to see some fluffy white corrosion just under the wire coating of the battery post clamp

Good diagnosis can only happen if the basics are right. I've seen people trying to diagnose codes with dead batteries thinking that will work. The ground straps can be the same on these older cars now.