stereo wiring guide for 78 caprice

trying to install a stereo i know i got some pos and negs mixed up

Best option is a wire harness. Other than that your meter will tell ya pos and neg.  It may help if you tell what kind of radio your installing. The more details the better. I dont see a wiring guide for that car at this site.

As boomer said, a wiring harness would be preferable; the Metra part number is 70-1677-1. That harness will work if your radio has 3 plugs with 4 wires each, and one plug with 2 wires. If your radio has a different setup, or the harness has been cut and you can't reattach it, the wires should be as follows: 12v constant - orange 12v switched - yellow ground - black LF speaker positive - brown LF speaker negative - yellow RF speaker positive - dark green RF speaker negative - light green LR speaker positive - gray LR speaker negative - tan RR speaker positive - dark blue RR speaker negative - light blue