So I've been doing work on this guy's 1999 ford ranger and I found out that the inertia switch was faulty and causing the fuel pump to not have power. While I suggested a new switch and connector, the guy insisted that I just bypass it. The connector was a little melted, I'm not quite sure what could've caused that, but regardless, I bypassed the switch. Its a 3 wire connector, so I believe 2 main power wires and 1 wire that turns on an indicator light on the dash. I wired the 2 main wires together and it worked just fine! Now a few weeks later, the guy messaged me saying the car died and started smoking from under the dash. What did I do wrong? Did I miss a step somehow?

 

It seems something was already going on that melted the connector you mentioned and probably burned up the switch as well. By bypassing the problem you are now allowing something else to be burned up which is why you have smoke. So by him asking you to bypass the faulty switch you never figured out why the switch failed in the first place. My guess is a new switch would have failed as well for the same reason. Someone with more electrical knowledge needs to troubleshoot this before the whole truck goes up in smoke.