My red XR2 had a 'security switch' in it, that a previous owner installed and I was totally unaware of.
They hid a piece of speaker wire with a switch under the dash. It was wired in series with the ignition coil.
When getting the car running/roadworthy, I thought it was extra un-needed wire, and removed it. I spent ~3 days troubleshooting trying to get the car to start again. I nearly replaced the engine harness. I noticed it at the last second, it was tucked under the fuse box in the engine bay.
This system would have provided a lot of voltage drop to the coil, reducing spark energy. Would not recommend. Extra headaches if you forget about it, or someone else is trying to work on your car.