Do I have to buy a code reader or can I use an LED? What terminals do I use and where is the plug?

 

87 2.8 EFI

 

You can try the LED method, but I personally have never done it successfully and do not know anyone who has (my friends who used to try the LED method now bring their trucks to me since I bought a scanner)

You can pick up scanners for relatively cheap now starting at about $60.00, I recently saw that even walmart is selling them now.

As for the diagnostic plug location, generally they are mounted to the bottom of the dash to the left of the steering column, kind of sandwiched between the steering column and the emergency brake release. There are some that are mounted on the bottom of the dash right above the tranny hump. Another place to try (due to age of the veh.) is in the engine compartment on the drivers side sitting in with all the other electronics ie. fuse block, batt., anti lock brake unit.

 

ok, got the code at autozone. Easy jumper and read of the Check Enging Light. Code 12. Any one know what code 12 is?

 

Here's a quick reference for you:
TroubleCodes.net/GM

12 == Diagnostic Mode

Basically it just confirms that you are in diagnostic mode and if there were more codes, they would be listed after the 12.

 

Code 33 MAP sensor voltage high. Where's the MAP Sensor?

 

MAP == Manifold Absolute Pressure

It is a sensor that reads the vacuum in the intake to calculate engine load.