I typed in the title wrong, it is in fact a 89 pickup

I know this is a chevy forum but this GM should be the same under the hood for all intents and purposes.

I have this 89 Chev 1500 pickup in the shop with a V6. The thing has no spark. I followed the testing outlined in the Hanes manual, confirmed that it has 12volts to the coil but nothing comming out, I put an HEI tester on the coil wire and nothing. Any ideas what the problem is and where I should look. If it makes any difference the owner hooked up jumper cables backwards and fried the computer as we had to replace it to get the fuel pump to come back on.