Tachometer RPM do not match engine/Secondary cooling fans on all the time

This past Thanksgiving day driving on the freeway and hit a pot hole pretty hard. I glanced at the tachometer and the needle was in the red line area. As I pulled off the freeway coming to a dead stop, the tach meter was at 5-6000 mark. The next morning, I got the repair manual out and ran diagnostic test and the error code came back as code 42. Turning the key to the on position - engine had not been started, I noticed the secondary cooling fans came on. As per the manual, I erased the error code, and started the car - no fans. Idling for 1 minute, the shut down. Retest the diagnostics - key on-engine off - fans are back on.
The tachometer - with the key in the off position - needle is in rest position. The key in the on position- engine off showed a little movement - but still below zero. Key in the on position - engine on - rpm jump to over 5000k,
Acceleration causes the needle past 6000k into the red line area. Key in the on position engine on - AC on needle jumps to 3500 rpm engine idle. AC off engine idle - rpm dipped for 2 seconds and then back up to 3500 rpm. I have never had the fan problem until the tachometer problem started, so I'm inclined to think the there is a ground or short problem within the same circuit? The manual says that a code 42 is usually caused when the ECM shows voltage problems within the ignition system (distributor, coil, ignition module). Does this system regulate the tachometer and the secondary fans or do I have 2 separate problems?
Any assistance would greatly be appreciated. The next step in the manual calls for removing the ECM connections with a special tool that I do not have and probing the connectors with a multimeter and test light- both that I do have. I don't feel comfortable removing the ECM connectors without this special tool, as according to the manual, alot of damage can arise from using anything but this tool.
Is the a different route you would take to fix these problems? I am a novice at best and I really don't feel comfortable working on cars but unfortunately I do so out of necessity and not by choice. Again any tips, theories, or direction would greatly be appreciated.
Thank You