1990 Chevrolet Astro How do I check and adjust the timing

Disconnect the tan/black wire EST (electronic spark timing) by-pass connector located near the heater housing in the engine compartment on the S/T series, or near the distributor on all other V-6 models. Do not disconnect the four- (4) wire connector at distributor. Connect the timing light to the No. 1 spark plug wire. Check timing and adjust to "0" degrees BTDC. With the engine off, reconnect the EST by-pass connector and clear the ECM trouble codes by disconnecting the battery.