Really need help, kill switch 94 caddy seville

Here's the easiest way. It will probably draw a bunch of argument about not being a "true" kill switch for some EE reason, but I'm not an EE and this will pass the test that tech uses. Others might have better ideas, there are certainly about 1,000 wrenches on this forum that are better, smarter, and more experienced than me. But they haven't answered you yet My method might be really hard on alternators since it's not providing some elusive back channel for the drainage of electricity, so use at your own discretion.

Get a 4-terminal kill switch like the one from Longacre. Run a battery cable from the positive terminal of the battery to one of the main posts on the switch. Run another cable from the opposite terminal to wherever the battery cable regularly runs (probably to the main fuse block). That kills the battery circuit and is the first half of the equation.

Now for the second half of the equation. I'm assuming that you are using the regular keyed ignition switch. Your ignition switch will have one wire that is always hot with 12v. When the key is turned to the "on" or "run" position, the switch bridges that wire with another wire that probably goes to the main relay in the fuse box and allows power to flow to the rest of the car. Find that always hot wire and cut it. On the side that is still always hot, splice in a wire and run that to the third terminal on the kill switch. Take another wire, attach it on the 4th terminal, and then splice it to the other side of the wire that you just cut. Now you have a "run" circuit that gets killed when the kill switch is turned off.

Again, I'm warning you that this might not be THE BEST solution. But it does work to (a) kill the engine (at least on my car) and (b) pass tech. That's just my 2 cents. YMMV. Cheers.