Main fuse box, all hot when car is on?

[JHZR2]

This 1993 300SD project Im tinkering on lost all seat and tilt wheel controls. Weird, they worked fine then didnt...

I started probing in the fusebox, and found that not all fuses showed 12V. I didnt see 12V on the fuse that feeds the seat and wheel control.

Question is why... I looked at the fuse box and didnt see 12V there. On the fuse or on the terminals...

I think that the seats and wheel tilt should be always hot. I recall it working with the car off, but havent had enough experience with the car to remember.

But fundamentally, shouldnt all the fuses underhood be hot at least when the car is switched on/running?

 

[wpod]

Heat comes from resistance.

 

[Leo99]

Heat comes from resistance.

Think he means hot = 12V between the terminals.

I'd assume all fuses are hot either always or when the ignition is on. So, all should be hot when the car is running. Some cars have more than one fusebox.

 

[JHZR2]

Think he means hot = 12V between the terminals.

I'd assume all fuses are hot either always or when the ignition is on. So, all should be hot when the car is running. Some cars have more than one fusebox.

Agree. Hot means 12v.

I found the wiring is continuous. Seems like the issue is 12v in the fuse box.

 

[mk378]

There are often relays to energize accessory circuits, instead of running all that current directly through the key switch.

 

[hemitom]

There are often relays to energize accessory circuits, instead of running all that current directly through the key switch.

This !

 

[JHZR2]

There are often relays to energize accessory circuits, instead of running all that current directly through the key switch.

No doubt. But I’d assume that the fuses are closest to the source, and the relays are downstream of that. You want to protect the whole conductor, not just part.

 

[JHZR2]

This is what I needed to know. Fuse section T is fed by a relay. The relay must be loose or faulty.