Aux Switch Amp Ratings

[FTW1996]

I have a 2024 Rubicon X and I'm in the process of installing a KG-1000G+ mobile unit. The unit requires a 15amp fuse and I am planning on connecting it to Factory Aux switch number 4 which is on a 15amp fuse according to the Jeep owner's manual. I'm tying into the switch with the wiring under the passenger dash rather than the wiring in the engine bay. However, when I look at the factory wire for switch number 4 under the dash (the dark blue and pink wire according to the manual) it doesn't seem to me like it's of sufficient gauge to carry up to 15 amps. It looks to me like it's an 18 gauge wire. I've always thought that you need at least 16 gauge wire for a 15 amp circuit. I'm no electrical wizard, so maybe I'm wrong.

So, my questions are:

1. Do any of you know for sure that the wiring for Aux switch number 4 is truly sufficient for up to 15 amps?
2. I don't see how such a small wire can carry that kind of amperage, but why else would Jeep say it's 15 amp circuit?

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[PT's19Rubi]

This is the switch assignments for the 2019. If the wire colors are the same, the chart is probably good for yours.

 

[PT's19Rubi]

Okay, just noticed that you know the above.

Typically, a fuse is sized at 1-1/2 times the intended load. So, the max load for a 15 amp fuse should be 10 amps.

 

[FTW1996]

Thanks for that info. I have another question. The manual for the KG-1000G+ says: "The specified fuse current is 15A. The specified power current is 20A and above." I'm not sure I understand this. Do you think they are saying that the wire gauge should be sufficient for at least 20 Amps, but to use a 15 amp fuse on that wiring?

 

[PT's19Rubi]

Using the 12v wire size calculator Here:
12v, 15a, 2ft run = 17 gauge wire (17 hard to find - round down to 16).
And, 12v, 20a, 2ft run = 16 gauge wire.

Given that the fuse should blow at lower current than the wire capacity (and load device), you should be good with 16 gauge. Overkill with 14 gauge.

Also, for what you quoted they say, I'm not sure either.

 

[THAW]

2. I don't see how such a small wire can carry that kind of amperage, but why else would Jeep say it's 15 amp circuit?

Wire capacity is also a function of distance.

The factory aux wiring is short and therefore won't cause significant resistance at the rated capacity.

 

[Terrymo]

You can use this wire size calculator from Blue Sea Systems. Plug in the numbers for circuit voltage (volts dc), load current ( amps), and the length of the conductor (feet). It will give you a general safe wire size for your project. Length is the round trip of the circuit, positive and negative.

http://circuitwizard.bluesea.com/

 

[Ratbert]

This is the switch assignments for the 2019. If the wire colors are the same, the chart is probably good for yours.

I'm thinking the wiring changed at some point after 2018.

 

[PT's19Rubi]

I'm thinking the wiring changed at some point after 2018.

Per the 2024 owner's manual, the aux switch wiring and fuse sizes are same as 2019 (per 2019 owner's manual).

 

[Ratbert]

Per the 2024 owner's manual, the aux switch wiring and fuse sizes are same as 2019 (per 2019 owner's manual).

For some reason mine (OEM) didn't match that.

 

[Left Field]

Thanks for that info. I have another question. The manual for the KG-1000G+ says: "The specified fuse current is 15A. The specified power current is 20A and above." I'm not sure I understand this. Do you think they are saying that the wire gauge should be sufficient for at least 20 Amps, but to use a 15 amp fuse on that wiring?

I believe the fuse(s) that come with the radio are 15A. On their website they have a 12V power supply as an accessory which is rated at 30A. The manual might be saying that the power source should be capable of providing at least 20A. The Jeep 12V system of course is capable of that.

The reason they may specify a 20A or more source is to ensure power stability during transient (momentary) conditions - such as the moment the mic is keyed. This would not mean the wiring (or fuse) would need to be rated for 20A as the steady current load is a fraction of that.

As others have noted, the distances are short and actual amperage is going to be significantly less than the fuse size, both of which create some leniency on the wire gauge.

Any idea of the wire gauge on the radio harness? That might give some indication of what they expect.

LF

 

[FTW1996]

Thank you all for your replies. Very helpful.

And to answer Left Field's question, the radio's wire harness is 16 gauge.

 

[Terrymo]

What Jeep engineer thought this was a good idea.

 

[PT's19Rubi]

What Jeep engineer thought this was a good idea.

Didn't notice that. Yeah, standing on your head in a foot well and you're supposed to be able to tell the difference between Pink/Orange and Orange/Pink. Hope there's a volt meter near by!

 

[FTW1996]

What Jeep engineer thought this was a good idea.

My thought exactly! a few months ago I built a battery box that uses a Redarc charger and needed to wire it to an ignition source, so I chose to go with that ignition wire under the passenger dash. Took me a while to figure out which wire was Pink/Orange vs Orange/Pink.

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