Engine bay switched 12v power

[ike84]

I recently ran wiring for a boost controller and wbo2 from the rear trunk to the cockpit. It's not at all hard to do. You sound rather convinced that you have to find a tpower supply in the trunk but let me know if you change your mind and I'll let you know where I ran my wires.

Stl is right - you have to take a lot of things into consideration when planning new circuits, unless the amp draw is minimal. The easiest thing to do is (for small sensors) run them up to the phone jack in the center console. For larger loads, use that switched current for a signal line to a relay which is run directly off the battery. Again, not difficult to do - I just ran 8ga wire from battery to engine firewall tonight in under 2 hrs (and that was with completely dismantling the shift console and running it under the carpet the whole way.

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[Stl-986]

I dont see any issues with mounting the device in the trunk, it does make sense. Requiring power to come FROM the trunk though is what makes no sense to me. Other then it just taking some time it's really not a big deal. That is how the wiring got there to begin with. What is there already has a purpose and it is sized accordingly.

It really should take only a couple of hours to run a wire to the distribution panel up front and wire into the ignition circuit. You can put the relay in the trunk but you need to get power that really on it's own and not fused with something else.

Not to say this will happen with this specific device but imagine you tap into a circuit that is also used by something such as the DME. The device you add draws more then the connected fuse and the fuse blows. You have now also shut off the computer and the car because of it. This is why when adding aftermarket items it is always best to go straight off the 12v source, use a relay, it's own inline fuse and if necessary trigger with ignition.

Keep in mind that most circuits have a fuse that is 10% or to the nearest size up of the devices connected. For example if a radio uses 12amp a 15amp fuse will be sized as will the wiring for 15amp. If lights will use 25amps it will be sized for 30 amps, etc. Rule of thumb is to add 10% of the load and go to the next size up.

[jaykay]

Thanks for the advice gents...some comments below..

Originally Posted by Stl-986

I dont see any issues with mounting the device in the trunk, it does make sense. Requiring power to come FROM the trunk though is what makes no sense to me. Other then it just taking some time it's really not a big deal. That is how the wiring got there to begin with. What is there already has a purpose and it is sized accordingly.


I am trying to avoid running wire from front to back if it is not needed. I dont often have much time to work on these things. The module and sensors appear to require the same ground location in order for them to work. Less complication in the trunk.

It really should take only a couple of hours to run a wire to the distribution panel up front and wire into the ignition circuit. You can put the relay in the trunk but you need to get power that really on it's own and not fused with something else.

Yes, I absolutely hate wiring and it would take me a lot longer than 2 hours. I am not electrically inclined enough to confidently splice into the ignition circuit. I have an idea but if there is procedure out there let me know

Not to say this will happen with this specific device but imagine you tap into a circuit that is also used by something such as the DME. The device you add draws more then the connected fuse and the fuse blows. You have now also shut off the computer and the car because of it. This is why when adding aftermarket items it is always best to go straight off the 12v source, use a relay, it's own inline fuse and if necessary trigger with ignition.

Very much agreed; hence the original post

Keep in mind that most circuits have a fuse that is 10% or to the nearest size up of the devices connected. For example if a radio uses 12amp a 15amp fuse will be sized as will the wiring for 15amp. If lights will use 25amps it will be sized for 30 amps, etc. Rule of thumb is to add 10% of the load and go to the next size up.

Thanks for this I will use these factors in the solution.

Originally Posted by ike84

I recently ran wiring for a boost controller and wbo2 from the rear trunk to the cockpit. It's not at all hard to do. You sound rather convinced that you have to find a tpower supply in the trunk but let me know if you change your mind and I'll let you know where I ran my wires.

Thanks for this. I am interested in your route. See the comments above regarding wiring hatred and common ground

Stl is right - you have to take a lot of things into consideration when planning new circuits, unless the amp draw is minimal.

Agreed. The load to be introduced is what it is though.

The easiest thing to do is (for small sensors) run them up to the phone jack in the center console.

Agreed but in this case the module will cover all sensors and it will draw 5 amps out the 7.5 available on the phone jack leaving not much for other loads.

For larger loads, use that switched current for a signal line to a relay which is run directly off the battery. Again, not difficult to do - I just ran 8ga wire from battery to engine firewall tonight in under 2 hrs (and that was with completely dismantling the shift console and running it under the carpet the whole way.

Impressive, I would be interested in your route. from the battery to the first firewall? The tricky part is from there to the trunk. I have 18 gauge in place under the console dedicated to other things at present. 8 sounds good for that long length and more current. Yes, I was really trying to stay away from console removal again...just finished some shifter bearings. Maybe use 16s as a puller...

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[ike84]

There is a grommet behind the battery that goes through the front firewall. That's the way from the frunk into the cockpit. From there run it back along the center console, tucked under the carpet, or along the door sill, whichever you prefer. From there go under the carpet on top of the engine bay cover. At the very rear bulkhead, you will find that the holes along the top communicate with the trunk. Just fish the wire through and voila.

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[jaykay]

Originally Posted by ike84

There is a grommet behind the battery that goes through the front firewall. That's the way from the frunk into the cockpit. From there run it back along the center console, tucked under the carpet, or along the door sill, whichever you prefer. From there go under the carpet on top of the engine bay cover. At the very rear bulkhead, you will find that the holes along the top communicate with the trunk. Just fish the wire through and voila.

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Yes I believe I have seen the positive battery cable connection go through this grommet. must lead to the big 80 amp current distribution terminal block on the inside....

Any tips for uncovering the passenger door sill route? the floor carpet seems to be really stuck in there.

[jaykay]

Has anyone identified a good ground in trunk firewall area that worked for them

Also under the dash? There are some spots but they look to be use by the airbag system so I dont wish to piggyback on those.

[Stl-986]

Trunk has one right by the DME
Dash - depending where exactly, I usually just make a new one with a self taping screw and not use factory ones.

[ike84]

I've not run anything under the door sill so I can't help ya there

Stl is right, there a ground on the trunk side of the firewall right next to the dme. Orr just make your own.

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[Starter986]

In the trunk. The relay box driver side. Slot/spot #10. I've switched power running a couple wires out of where the relay sits. I don't recall into where the two wires run. My mechanic brought to my attention that's where I'm missing the relay for the SAIS.

Power comes on when ignition is turned on. Shuts off power about 15 seconds after the key is removed.

[Stl-986]

Help Me DIY did a good video on installing seat heaters. It includes getting access to the wiring in the door sill. Take a look at it. Not all that difficult to do. Can be done with the seat in the car, but much easier with it out, which only takes a few more minutes.

[jaykay]

Originally Posted by Starter986

In the trunk. The relay box driver side. Slot/spot #10. I've switched power running a couple wires out of where the relay sits. I don't recall into where the two wires run. My mechanic brought to my attention that's where I'm missing the relay for the SAIS.

Power comes on when ignition is turned on. Shuts off power about 15 seconds after the key is removed.

Any chance you can post an image of this relay? Then I might be able figure out what is on that circuit and permissible current draw.

[jaykay]

Originally Posted by Stl-986

Help Me DIY did a good video on installing seat heaters. It includes getting access to the wiring in the door sill. Take a look at it. Not all that difficult to do. Can be done with the seat in the car, but much easier with it out, which only takes a few more minutes.

Thanks I will look it up. Was this the grommet you used or was it the big body plug right behind the battery? I try and get bigger pictures…..it is a real weird item.

[Starter986]

Originally Posted by jaykay

Any chance you can post an image of this relay? Then I might be able figure out what is on that circuit and permissible current draw.

I don't have a relay in that #10 spot... so informed by my mechanic. (That would explain why never have I heard my SAIS come on.

Use an electical testor in the slot where the relay goes to find which "power" is ON. The two slots in mine power up when the car is turned on and shuts off about 15 seconds after the key is removed. I do not know what is the current draw.

[ike84]

Originally Posted by jaykay

Thanks I will look it up. Was this the grommet you used or was it the big body plug right behind the battery? I try and get bigger pictures…..it is a real weird item.

Big rubber grommet behind the battery, opens up into drivers side foot well just under the dash. I think what you've taken a picture of is correct.

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