Adding Accessories

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Sekred

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#1
Recently I fitted a boost gauge and naturally had to connected to the engine but also add an electrical connection so the gauge illumination would function.
Silly me thought I could just pick up power from the OE dimmer switch but I forgot that modern vehicles are covered with control modules that ?speak? to each other using a method called ?Multiplexing? and use a standardise high speed data link, known as ISO CAN 2.0. Splicing into wiring looms is not really an option.
I decided to add an accessory circuit to the vehicle so I could power the boost gauge and also in the future add further accessories that worked when the ignition was in the on/run position.
I used a fused 5mm wire directly from the battery and ran it into the interior to a 40amp relay and from the relay to 6 position fuse panel where my accessories would be connected.
I know needed to pick up power to activate the relay when the ignition was on. This became a challenge because of a number of reasons. I had no wiring diagram, the fuse positions shown in the owner?s manual are different to the vehicle and a lot of the fuses are on the ground side of the circuit. I eventually located a power source through some trial and error. The problem was picking up power from the selected circuit and this is where I came across a useful device. You simple remove a fuse from where you want to pick up power and plug in what is called ?Add a Circuit?. The original circuit retains the same fuse and you end up with a fused breakout wire'

OEM fuse panel and breakout wire.
View attachment 203

The device called "Add a Circuit".
View attachment 204

Added fuse holder
View attachment 205

One thing to keep in mind when adding accessories is current draw, how much extra load you add to a circuit that is not designed for it. Even something only drawing 5amps won't be enough to cause a problem with the wiring but it cause a CEL to come.
And lastly but most important and obvious is FUSE everything. The last thing you want to do is burn your FiST to the ground!

One more last thing, this YouTube clip explains Multiplexing and also plugin and play.

[video=youtube_share;ASDPhEw-9XI]http://youtu.be/ASDPhEw-9XI[/video]
 

MKVIIST

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#2
Thats a great write-up. I never thought about using the ATM Add-A-Circuit to tap into the fuse box.

Did you end up using two fuses on the Add-A-Circuit for your gauge?

I found one on Amazon for anyone who is interested.
 
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S

Sekred

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Thread Starter #3
Thats a great write-up. I never thought about using the ATM Add-A-Circuit to tap into the fuse box.

Did you end up using two fuses on the Add-A-Circuit for your gauge?

I found one on Amazon for anyone who is interested.
Yes, retained the fuse for OE circuit and a 5amp for the gauge.
I am no Auto Electrician by the way, so members feel free to add or disagree with what I have done.
 

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