where does power from fuse come from?

Thread Starter

louka

Joined Oct 22, 2020
2
So I want to add cabin lights to my car fuse box. I have a fuse adapter 1 input 2 output. The original fuse goes in one slot on the adapter. The cabin lights will go on the other slot. the cabin lights are 12v 18watt 1.5amp. if the fuse connected to the fuse box is a 5 amp fuse, will the circuit with the lights only be drawing 1.5 amps?? or will 5amps be coming from the fuse? and the adapter only has a positive wire lead. will the negative just be connected to the metal frame of the car?
 

MrChips

Joined Oct 2, 2009
22,107
A fuse is a safety device. Exceed the fuse limit and the fuse blows.
A 5A fuse does not supply 5A. You can take as much as you want from 0A to 5A. Exceed 5A and the fuse blows.

Yes, negative is the car frame.
 

Thread Starter

louka

Joined Oct 22, 2020
2
A fuse is a safety device. Exceed the fuse limit and the fuse blows.
A 5A fuse does not supply 5A. You can take as much as you want from 0A to 5A. Exceed 5A and the fuse blows.

Yes, negative is the car frame.
Thank you!!
 

Hymie

Joined Mar 30, 2018
881
Mr Chips said:-

'You can take as much as you want from 0A to 5A. Exceed 5A and the fuse blows.'

If only that were true – as good rule of thumb, a fuse can pass 1.6 times its rating indefinitely, at 2.1 times rating it should operate within 30s (depending on the precise rating curve).
 
The way things used to work is that you would have an ACCESSORY side and an IGNITION side in the fuse box. ACCESSORY is live all of the time.

With the fuse out, you should be able to determine the HOT side.

The ends of the fuse (blade fuses) are exposed so you can access them as test points.

Now there are multiple fuse boxes in various locations and whats known as "Retained accessory power" which I have no idea how it works. All I know is the radio turns off when the door opens. I THINK you have to add gizmos to one of the cars control busses to create another.
 
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