Converting always on cigarette lighter to switched power

[Electrocuted]

So my car's cigarette lighter is always powered even when the car is switched off. I am attempting to make it switched so that the power is only on when the key is turned to accessory. I made a basic drawing of the fuses I want to connect.

I have seen a few ways people are doing this. One way is by using an add-a-circuit fuse tap

where the pigtail end goes to fuse 1B and the plastic part (where the 2 fuses are on top of each other) goes to fuse 2 with the left blade going to 2B. It looks a little something like this

I don't really understand why it's done this way when in my mind, I should get an inline fuse holder

and just connect one end of it to 1B and the other end to 2A. Would that work safely? I would leave fuse 1A and 2B empty and my cigarette lighter become switched on when the key is turned to accessory. Not sure why I need 2 fuses with the add-a-circuit when all I want is switched power.

 

[Diver300]

The add-a-circuit fuse holders have two fuses so that one replaces the original fuse and the other provides fusing for the additional circuit. You should still keep fuse 1 with the same value as before to run the item you have called “some device”. You also should have a second fuse to power the cigar lighter socket in case it gets shorted.

One thing you need to check is that 1B does turn off when the ignition turns off. On some cars, some circuits that turn off when the ignition is turned off leave the fuse live, and if that circuit is arranged in that way you will need a different approach.

What you want:-
Battery -> switch controlled by ignition -> fuse -> “some device”

What you don’t want:-
Battery-> fuse -> switch controlled by ignition -> “some device”

 

[Electrocuted]

The add-a-circuit fuse holders have two fuses so that one replaces the original fuse and the other provides fusing for the additional circuit. You should still keep fuse 1 with the same value as before to run the item you have called “some device”. You also should have a second fuse to power the cigar lighter socket in case it gets shorted.

One thing you need to check is that 1B does turn off when the ignition turns off. On some cars, some circuits that turn off when the ignition is turned off leave the fuse live, and if that circuit is arranged in that way you will need a different approach.

What you want:-
Battery -> switch controlled by ignition -> fuse -> “some device”

What you don’t want:-
Battery-> fuse -> switch controlled by ignition -> “some device”

Thanks, I'll have to double check 1B if it's off but I'm pretty sure it is. If not, I'll look for another location.

I think I messed up when I said the pigtail end should go into 1B when it should go to 1A. I drew up this updated diagram. I'm going to crimp on a spade/blade connector to the end of the pigtail. Does it look right?

 

[Electrocuted]

I'm an idiot. I revised the drawing so the fuse tap plugs into fuse 1. Is this the correct way?

 

[Diver300]

I'm an idiot. I revised the drawing so the fuse tap plugs into fuse 1. Is this the correct way?

View attachment 145480

Your revised drawing looks correct.

I don’t know which fuse on the add-a-circuit feeds the cigarette lighter and which feeds “some device” so you will have to work that out if the fuse ratings are different.

 

[Electrocuted]

I think I'm starting to understand this whole add-a-circuit fuse tap. What led me to originally ask the question about this whole install is that I saw some empty fuses in my fuse box and didn't quite understand this fuse tap with empty fuses.

If fuse 1 in my original drawing was empty but still had switched power and "some device" is just to indicate the device side of the fuse, would it be ok if I just use an inline fuse holder and connected one side of that fuse holder to 1B and the other to 2A? 1A and 2B would be empty.

 

[Diver300]

I think I'm starting to understand this whole add-a-circuit fuse tap. What led me to originally ask the question about this whole install is that I saw some empty fuses in my fuse box and didn't quite understand this fuse tap with empty fuses.

If fuse 1 in my original drawing was empty but still had switched power and "some device" is just to indicate the device side of the fuse, would it be ok if I just use an inline fuse holder and connected one side of that fuse holder to 1B and the other to 2A? 1A and 2B would be empty.

View attachment 145483

That would work as long as fuse 1 wasn’t fitted originally. Also my warning in post #2 applies.

 

[Electrocuted]

Just wanted to update that I did end up using an inline fuse holder and connecting it to an empty fuse slot and it worked perfectly. Thanks Diver300