You can either use a DVOM or a 12 volt test light.
http://www.autopart.com/tools/toolsmain/tool/T_3023.htm
A test light is easier to use for this year vehicle. I disconnect the negative cable and install the light between the negative terminal and the ground wire.
If the bulb lights you have a drain on the system. Unplug each fuse one at a time until the light goes out. If this don't work unplug the fuel pump relay they can stick. An alternator can also ground out check this. External voltage regulators are a big cause of this type of problem. I think Ford used external in 1984 but I'm not certain about GM but I they used internal voltage regulators at least on pickups. Also check the relay for the computer system.