At Annual Tech last month my car failed because the kill switch didn’t kill the car. I don’t mean kill in the Road Atlanta Miata punt-n-run sense.
It came as a surprise that my kill switch…didn’t. It certainly used to… And the only thing I’d messed with the wiring junction on the right firewall when I was putting in a fan relay a couple months ago.
So after my car REALLY died an hour later, I had time to go around and take some pics of how other people had the wiring junction, well, wired.
What I found is that there is a fusible link back near the battery that was blown. As you probably know we have 2 wires coming from the battery. The big wire goes to the frong wiring junction at the front firewall, and then goes to lots of other places. That’s the wire that everyone interrupts with their kill switch. The small is the one with the fusible link. It goes goes to the wiring junction too, but it’s isolated from the big wire at the junction, and goes to the fuse box, and from there to the ECU maybe. I heard a rumor that the ECU likes it’s own power supply.
I think the the PO was forced to wire the firewall wiring junction funny because the dead fusible link was at the time some electrical mystery. Then I R/R the wires on the wiring junction a couple months ago, do it right, but the isolated wire at the junction isn’t hot so I had to put in a jumper. It seemed pretty strange that the jumper was required at the firewall, but it worked. A little too well.
The failure of the kill switch forced me to look harder at why the small wire from the battery was cold. And that’s when I found the fusible link.
In the pic below look closely at the battery wire just to the right of the fire extinguisher mount. The fusible link creates a thick spot in the plastic insulation.