DAMNED 99' ES INTREPID WONT FRIGGIN' START!!!

Here's the lay of the land...Installed a siren under the dash about 4 days ago for job purposes...it supposed to interact with the horn ring when pushed..long story short- about 2 days after installation I pushed the horn/siren and all of sudden the engine dies...Tried to crank right after- and NOTHIN..

Got it to the mechanic, he sez siren had absolutely nuthin to do with the engine, so he hooked up the troubleshooting device you plug in under the dash. Everything seems to be good, yet he does the following..

1. Checks the plugs-pulls em' theyre firing.
2. Checks the fuel pump & injectors and gas pressure..gas is fine.
3. Checks all the relays and fuses, under hood and in car..they're okay..
4. Checks main computer, everything is in order.
5. Checks and buys new cam shaft sensor, that's not it....
6. Checks timing and uses doohickey to see if piston pressure is okay. OK
7. Even uses ether to try to get it turned over..it backfired from spark.

From what I have seen while standing over the guys shoulder, the troubleshooting device sez everythings in order..the upstream sensors, the camshaft sensors, the 02 sensors, the Autoshut-down sensors, everything across the board green.

However I called a friend, he mentioned..is the check engine light on when you try to crank it?? Well, my answer is when you turn key to on pos. it comes on and goes of in three secs. But when you try to crank and hold key, the crank engine lights blinks rapidly. and that's the story. The car is high in mileage, at 156k and never had this problem before.

IF ANYONE OUT THERE KNOWS HOW TO GET "CODES" BY TURNING KEY, I'D APPRECIATE IT! thanks!

Well ladies and gents, I'm back as nobody has posted anything since...I have figured out the way to get godes from the car with the whole turn the key deal. I have codes p1684 and p1495, which mean battery was disconnected within last 50 cranks and fuel leak detection in solenoid valve, both of which were investigated and do not contribute to my NEW problem.

The new problem as I have had a more experienced mechanic look at my trep is....He found out that there is a pulse going to the fuel pump sending gas to the injectors..but there is no pulse going to the plugs, as he had a plug pulled out and while i tried to crank it...NO SPARK! He had a little light stuck into the fuel injector plug which lit up numerous times while I was cranking the engine, showing there was current in for fuel. The long and short diagnosis of this problem is that...

THE 1999 ES 3.2L DODGE INTREPID IS A KNOWN FAULTY WIRING HARNESS VEHICLE..

It was explained to me that this car which I have invested quite alot of money into...has problems of MANY kinds and FACTORY RECALLS galore! he also explained in detail how his very own daughter had the same model car with the same problem...He says the only remedy is to get a factory/dealer NEW ECM computer programmed with my VIN# to assure the match.

He sez the car was dead with the computer which was in the car and one from the junkyard..but he got one NEW from the DEALER programmed with the VIN and WHAMMO! she was off and driving like nothing ever happened!

My question to you guys is...has anyone on here experienced this, and if so did the new computer work magic too?

Does anyone know where you can get aftermarket ECM'S from??