Look, I've owned Triumphs, there's nothing you can tell me about all the ways a car can catch on fire. Our TR-6 caught on fire TWICE. In our case, it was a transitional model (iirc, a '76, it had the square tail lights anyhow) which included both the stalk dimmer switch and the old style foot dimmer. If you turned on the stalk dimmer switch while the foot switch was already in the on position, it created a dead short through the battery that bypassed the fuse box (a careful study of a schematic revealed that this was overlooked by the designer -- and they say Ford has bad electrical engineers, they are nothing on Joe Lucas's men.)
The carburetors also had a tendency to leak, and if a diaphragm ruptured (thank you Stromberg) it could spray gasoline on the hot manifold. That never happened to us, thank goodness, although the diaphragms ruptured often enough that we had an impact wrench and two sets of spares in the trunk.
We had three fire extinguishers strategically positioned in the vehicle.
And it must be contagious, because while we were parked at the grocery store, the Chevy Nova NEXT to us caught on fire. We were able to put it out promptly, anyhow.
Actually, not *quite* how it works.
Ford decided in their infinite wisdom to make the cruise control “brake cancel switch” a pressure switch on the master cylinder. And then they decided to leave it powered all the time, even when the car was turned off. Yup, the cruise switch still had power flowing to it even though the engine was turned off and keys were removed. That’s just bad design - why would you leave that switch powered????
The poor workmanship enters the picture (and causes the fire) when the poorly made switch begins to leak and brake fluid enters the switch. This causes a short, the brake fluid starts heating up, and then it passes the flash point... with a BOOOOM coming up in short order.
The telling point is that this doesn’t ever happen with the engine on. That’s because there is a cooling air flow over the engine and the master cylinder which keeps the temp below critical when the car is running or in motion.