Route Through the Firewall Question

[Fellows]

Hi All

A quick question for anyone who's ever had to run a power cable through the firewall from the battery.

What routing did you use, and where did you put the cable through the firewall? I ask, as having had a cursory look, and nowhere obvious jumped out at me as beng an easy point to get though it.

All help appreciated. Thanks.

 

[Tay-FR]

I ran it through the grommet behind the airbox. It was a pig of a job to do but managed to get 4 gauge power cable through it

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[Fellows]

Thanks, I'll have a look. Do get to the cabin side of the grommet, does much interior have to come out?

 

[Tay-FR]

To make life easier take the glove box out. You could possibly do it without but it would be VERY fiddly. Then of course the side trims and lower B panel trims to run cable through to your boot. Again you could possibly leave these in situ but it makes it so much easier.

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[Fellows]

To make life easier take the glove box out. You could possibly do it without but it would be VERY fiddly. Then of course the side trims and lower B panel trims to run cable through to your boot. Again you could possibly leave these in situ but it makes it so much easier.

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Cheers, I'll start stripping it out...!

 

[DorsetChap]

There is a 30A terminal block in the lower console fascia / above the brake pedal, so it still involves removing interior trim but doesn't necessitate routing wiring through the firewall. I've not removed the glove box but I have tapped into this terminal block and found removing and replacing the trim fairly easy. No idea how to post photo's but if you Google "Golf mk4 power terminal" and look at 'Images' there's a labelled photo on the 3rd row (on my pc). You'll probably still have to find an accessible place for an inline fuse - I tucked my fuse into the right hand side trim of the driver's footwell (obvious when you're rooting around in the footwell).
As an aside, there is a cable route under the windscreen scuttle then through the grommet that seals the bonnet release cable. I'm struggling to describe it in words but I can say that I found it very easy to install some wiring from my engine bay to the cabin using this route.

 

[Tay-FR]

It all depends on the power drain of the amp you are fitting. If you only want a relatively small amp then the 30 amp connection should be fine. Take a look at the fuse/s on your amp, if they are more than 30 amp you are likely to keep popping the fuse or burning the wiring out.

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[DorsetChap]

Oh, I didn't appreciate that the OP was installing a power amp but Tay-FR's advice to check the power draw is very wise whatever is being installed. I had removed a previous owner's EBC power supply from the battery because it was snaking all round my engine bay, and was permanently live too! Using the terminal block tidied up the wiring and I used a switched (i.e. power only when ignition on) terminal.
Hope the OP isn't reading all of this with the glove box already out and on their lap !

 

[Fellows]

Thanks for all the feedback. Happily I've not pulled anything apart yet!

My amp has a 30a fuse in it. I take it there should be no problem in running the amp off of the terminal in the dash?

 

[Tay-FR]

I guess this all depends what you are looking to achieve? If you want a system with a bit more power that the standard stereo it 'should' be fine.
If you are looking for bass then personally I would run separate power cable fused within about 6 inches of the battery, I wouldn't go less than 4 gauge especially if there is a chance you may want to expand your system.


But then I love my bass

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[DorsetChap]

FWIW I feel Tay-FR's is spot-on. If you're installing a skull crushing sound system then a dedicated fused power supply direct from the battery is the tried and tested method. Save the terminal block for other widgets like gauges, USB, etc. Technically you can connect any number of things to the block provided that the cumulative current draw doesn't exceed the power rating of the terminal. At present I have a w/m pump and EBC running off the terminal block which draws 10A and 1A respectively. For my purposes I feel using the terminal block is far more elegant than tapping into the ignition wiring, piggy back fuses, etc. The terminal block seems to be VAG's best kept secret so hopefully just knowing about it will be of use to forum members.

 

[Tay-FR]

I'm not sure if the attached picture helps but you can see roughly where the cable goes

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[Fellows]

Thanks for all the wise words, they're much appreciated.

I will initially just be running a little 150W (peak) 2 channel amp. Probably later, I will add a small 8'' active sub, so not big at all.

I'm not after show systems or anything of that nature. Just a bit more power to the sound. As I'd be running two units off of the feed, I would probably go down the separate feed route (even though I'd not be running anything very powerful).

To calculate what one could run off of a feed, do you just work out the current from the quoted RMS? I'm pretty ignorant on this point I confess. Previously I've just grossly over-specced the cables to ensure safety!

 

[Tay-FR]

Is been a few years (25 cough) since I did anything with ohms law so had to search.

This might help you work it out?

Taken from this link
http://www.diymobileaudio.com/forum...ar/64710-what-my-amplifiers-current-draw.html

You need to start with your given power (power is measured in watts) so your amp puts out 300w with what, 13.8v of potential voltage?

So with that being said, 300w / 13.8v = 21.74

So your amplifier, with your charging system sitting at 13.8 volts, puts out 300w, and your current draw of your amplifier is 21.74 amperes (amps). Looking back, this isn't quite the answer you want?

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[Tay-FR]

From personal experience I have run 600w rms amps using 4 gauge cable with no issues. I have also used 8 gauge (thinner) without issue but reduced low level bass

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[Fellows]

Cheers for that - I've just looked at some tables and done some simple maths and my modest projected system should be fine running off of 8 gauge.