my latest project... 04 S 120k
Found it with the battery completely dead, threw a charger on it and let it sit for a while... Got the standard flashing M & S lights (even with the car on a charger?) I got the car to do the starter solenoid click click click like the battery was dead so I waited a bit longer. Now I get nothing when I turn the key. Tried it in park and neutral. No blown fuses under the hood. Tapped the starter with a hammer and no difference. The security light is not on or flashing. Anything else electronic to check before pulling the starter out?

 

loose or dirty battery terminals maybe?

 

I looked briefly at the connections and they looked fine... The fact that the starter wont even click (after it did click the first time) leads me to believe its something else.

 

Check your grounds to the frame. Is there power to anything....just won't crank or complete blackout on the truck?

 

Have you tried swapping out the battery with a known good battery? It could be the battery is to far gone to hold a decent load. There should also be a ground near the alternator bracket that you might want to check.

 

It takes about 10 minutes of sitting with a good battery, sometimes, for the IDM, ECM, and BCU to all finish talking to each other.

I'd let it be for half an hour after charging the battery, come back and unlock the door and try again.

If you still don't get anything, before pulling the starter, see if you get power to the solenoid when you turn the key. If not, there is something else other than the starter having problems.

 

Also, the M&S lights are for an automatic transmission error of some sort. It could be the XYZ switch won't let you crank because it doesn't think you are in park or neutral. Does the indicator on the dash show you are in the correct gear? I've also seen the M&S lights with BCU problems or just the wiring not plugged in snugly. I guess the XYZ signal must go through the BCU connector?

 

Locked it last night, just unlocked it this morning, turn the key and get no starter click. The rest of the truck has full power, dash gear indicator is in line with the shifter (ie park says P neutral says N) M & S still flashing as I expected.
Alt to battery ground is good, battery to body is good and braided strap from the D/S head to firewall is good.
The fact that it attempted to turn over before is what has me confused (or in denial that I need a new starter). Last thing to check is power at the solenoid I guess...

 

Flashing M&S can be triggered by a low battery/loose connection. I had that problem and charged the battery and cleaned all connections and went away. My battery was low due to sitting for several months while I was working on the engine but, it's old anyway and if it comes back I will buy a new battery.
I see you have tried all of that so, may not be your problem?
Try switching the key on and off several times to see if the flashing M&S stops.
Also have you tested your starter manually from underneath with jumper cables?

 

I would do that 1st and/or hook up one of these remote start switches to that is part of a compression tester kit. Problems like this are sometimes easier work backwards on....is the starter good? If so, is the solenoid good? and so on until you find the problem.

Also, does the inertia switch cut power the starter on a Disco or just the fuel pump? That's an easy one so maybe check that too. It's on the firewall.