Here are some web sites with the basics on retrieving codes without a scan tool or code reader.
Poor drawing of ALDL but ok instruction + codes
http://www.cfm-tech.com/gm_tbi_trouble_codes.htm
OBDI terminal identification
http://robertpowersmotorsports.frees.../ALDL_plug.jpg
OBDI illustration and instructions
http://www.troublecodes.net/GM/
1985 – 1990 trouble codes instructions
http://www.iroczone.com/specs/TroubleCodes.htm