99 boosted, leads reversed - no start

The damn shuttle drivers at work do this all the time. 99 times out of 100, what happens is the main fuse for the whole electrical system (80 amp, sometimes more) blows. Not sure where it is on our discos, but on most new cars it's right there at the positive terminal. I don't have RAVE in front of me, but I'll take a look when I get home and see if I can figure out where it's at.

Are you checking the fuses visually or actually check power in and power out?

Might get lucky and have it be a fuse or a tripped inertia switch. Reset the switch and check all circuits with a voltmeter.

But having seen this same scenario a couple times before - you're probably looking at a new ECU - they usually can't handle the reversed polarity.

I thought flashing S and M means the battery is too weak or bad connection. Did you clean the crud off the battery connectors/posts with a wire brush? I would try that.

If you're lucky, they blew the 100A megafuse in the underhood fusebox.

If you're not, they fried any number of the on board computers. The ECU, BCM, SLABS, pick your poison.