I have a 2005 Mustang GT. I have Autometer Monster TACH with the Adapter for current Mustangs. However, I do not have any real instructions on how to install the unit. Anyone out there who could share some help or expertise would be greatly appreciated....thx,

 

You will need to get the RPM signal from either a coil or an injector. Any coil or injector will do. If you have the adapter you should have no problems getting it to work. Didn't it come with instructions? If not I would suggest looking at Autometer's website. Failing that just take the part number off your adapter and e-mail them asking for the information regarding what connection does what and I am sure they will provide you with the information.
In regards to the tach itself, it's pretty straightforeword.
It will have a ground wire that is black. Tie it to a bolt or a crew in the firewall or any other convenient place that is metal on the car.
The red wire needs to go to anything that goes +12 volts with the ignition key in the "run" position.
Usually there is a white wire the drives the interior light in the tach. You can tie this to the back of the headlight switch. You can carefully pry the headlight switch out of the dash with a small flathead screwdrive and use a 12 volt test light to locate a wire that is energized when you turn on your lights. Prefferably one that changes intensity with the dimmer so that your tach lighting dims with the rest of your gauges.
The remaining wire, usually orange or green (depending on the brand and model of the tach) is your rpm signal wire, which in your case would connect to your tach adapter. As I suggested, contact Autometer for details on how to wire that.
I hope that helps.
I wonder if I could inquire as to why want to clutter up your interior with a Monster Tach when the factory tach is accurate and works well? Just curious.

 

Same as 281GT. I have a Raptor. Here is their instructions for the coil wire tapping:
http://www.raptorperformance.com/For...g_2005_46L.htm

 

maybe it has leds that blink o_O