Disconnect the connector, attach the negative multimeter lead to chassis ground, connect the positive to one of the four wires. Have someone turn power on. Repeat this until you see 12 volts. You may see one with about 5v, this may be for your fuel level gauge. I am only basing this off of the Bonneville 4 wire system. 2 grounds, 1 5V and 1 12v positive. Trial and error really. Once you determine which pin is 12v positive, look at the other connector and verify the pin, and then connect a wire to that pin and connect to battery.
1997 Pontiac Bonneville SEi-SCRAPYARD
2000 Chevrolet Blazer LT 4X4 4.3L
2002 Chevrolet *-10 LS Ext Cab 4X4 5.7 V8