It's been a while since I last had a look at this so as I had a couple of hours to spare this afternoon I thought I'd take another look.
Guess what................ I got it running!!!!!
I cannot understand how this happened but I noticed that fuse 19 was missing from the PDC. This is labelled up as PCM battery. I placed a fuse in there, turned on the ignition and all the gauges burst into life. Tried cranking it and it fired up and ran for a couple of seconds. Tried it again and it did the same. Looks like the SKIM was not recognising the key correctly and shutting the engine down. I wondered whether I had somehow mixed up the two SKIM modules that I had so I swapped them over. No luck at all now. The SKIS light was on permanently. Swapped back to the old SKIM and the SKIS light still remained on and the engine would now not start at all.
Strange!! So I dug out the second complete ignition lock assembly and fitted that along with the SKIM module it came with. Using the key that came with this assembly I was expecting it to recognise the key but for there to be some problems with using a SKIM from a totally different car to that which the PCM and BCM came from. I was pleasantly surprised when I turned the key, the SKIS light did its three second check and then went out. Turned the key further and the engine started and kept running. So it looks like you can use any SKIM module providing it has the matching key and that they are not 'keyed' to any other of the cars electronics. It means that I will now have two different keys for the car (one for the ignition and one for the locks) but I don't care because it now starts and runs!! It's miss firing like hell at the moment, probably due to standing for nearly a year. A set of plugs will probably sort that out. The code reader is telling my two of the coils are at fault but I doubt that is really the problem.
So, this fuse 19, PCM battery. I'm guessing that there is a rechargeable battery in the PCM and I must have removed the fuse when I was trying to solve the battery drain problem and forgot to put it back. The car kept running all the time that there was charge in the PCM battery but eventually it ran down and shut down some of the PCM systems. I know that there was other power to the PCM as I had checked for the reference voltage at the distributor and there was some data on the bus so the PCM must have been partially alive.
Well, the end of a nearly year long saga. I was determined that this car would not beat me!! Now to recommission it and decide whether to keep and and sell the Mercedes or just get rid of the Jeep. At the moment I want to get some use out of the Jeep - it owes me that!!