You can check your own with the 92. Not 100% sure about the 94 though. I don't have the exact steps to do, but you just need a jumper wire and a test light. Do a search and I'm sure you can find it.
[/quote]

Don't remember how to retrieve codes off of OBD-I vehicles. Usually a dash light flashing morse code 'tells' you what the code is then you have to translate the code. I don't know on the Mustangs how to get them into trouble shooting mode...

96 and newer vehicles are required to be OBDII compliant and thus have ports, anything prior was OBDII w/ w/o ports or OBDI. here's a link to show which cars in the 94-96 years were inbetweens...
http://www.obdii.com/connector.html

 

Actron CP9015 should do the trick for about $35. Pep Boys and I think Autozone sell Actron. Depends on the depth of the scratch. surface scratches can be polished out using 'gritty' POLISHING' compound, not to be confused with rubbing compound. HP increase would be 5-7hp tops. Level of diffculty..don't know. Never done it myself.