Hello new member, 04 expd 5.4. Truck has been running great ,sat for a couple of days because of christmas. Long story short ,tried to start it up it cranked over just fine but wouldn't start. After a little googling saw a video about inertia switch , pressed it and it started right up!! Does anyone know why that would trip?

Thank you in advance for any suggestions.

 

Maybe someone pranked you.

 

That switch doesn't "trip" like say a circuit breaker would. Instead it's meant to shut down the fuel pump in the event of a rollover. So for the switch to "trip" it would have to be turned upside down. If it happens again I would replace it.

 

I've read reports where a pot hole or curb strike can cause the switch to trip.
I thought the switch responded to a shock - https://en.wikipedia.org/wiki/Inertial_switch

 

Makes sense to me since such a jolt would cause a reversal a gravity for a few 10ths of a second as the truck goes up then down.

 

It's an impact-sensitive switch that is supposed to "trip" (like a circuit breaker!) when physically shocked. You should be able to trip it with a very firm slap to the panel where it's mounted.

Back in my SHO days, I had a tool box in the trunk of the ole '89. I went around a corner a bit too fast causing the toolbox to slam into the side of the trunk where the inertia switch was located. Had to coast to the side of the road, get out, open the trunk, and reset the switch to continue down the road.