Need Help and Advice with Car Audio Install

[Ferret]

Create yourself a secondary fused bus off the battery terminal - there's plenty of room under the rear seat to do this...

Buy yourself a good quality auto relay that's capable of handling upto 40 amps, and put appropriate guage wire to it.

Next, run a small line with your audio cables through the centre of the dash from the switched terminal of the ISO connector. Use this to flip the relay on and off!

I'll draw you a picture of what I mean later, but dinner's ready! Hope you see what I'm driving at there!

[leicesterboy15]

Well I've decided to upgrade my car hifi but I need some help and advice from anyone who knows anything about these things or anyone who has had any car hifi experiences! The main thing I am having problems with is power, heres the deal:

I'm installing an Alpine in dash monitor which has a separate hideaway box, the car already has an ISO plug installed. The stereo wiring harness has an ISO connector on it. The ground, Power and switched power split out of the ISO connector and go to the head unit AND the hideaway box. All other cables go directly from the ISO connector to the hideaway box. This box will be located at the back of the car so the harness has to go from the ISO connection behind the dash (with the aforementioned wires splicing off to the head unit) all the way to the hideaway box in the back of the car. This includes all the usual ISO stuff (speakers and power). I need to splice in an extension into this loom as it doesn't reach to the back of the car at the moment. I will also be running a TV Tuner, 2nd Screen and SatNav device all of which will be located at the back of the car, be connected to the hideaway box and need a 12v power supply each.

This is where I am struggling with what to do. All these units need power and what I did in my old similar set up was to run switched power from the Car ISO harness to back of the car and split out to all devices, this meant that everything was switched and nothing could accidentally be left on. But I could never turn the volume up because as soon as I did the unit would cut out then I'd have to quickly lower the volume when it cut back in again (I presume this is dangerous and not good for the hardware). I am assuming this was a power delivery problem.

My main questions are:

When I extend the harness should I use a higher gauge for the switched power or stick to whats there?
Will a higher guage make a difference if the cables on either side (I.e. to the OEM stereo connection) are a lower gauge?
Will a higher gauge constantly draw more power?
What gauge should I use / is a safe bet?
Should I run power for the other devices like I did before (one switched supply split to all units) or should I run them straight from the battery. If I do this is there a way of turning the devices off?
How do I work out the size of fuse(s) I should use? I will not be using any Amps at this stage.
Should I have one main fuse and one for each unit? What size should they be?
Should I split out the power from the speaker wire on the harness even though they are part of the same harness out of the Alpine factory?

I am pretty confident with the other connections as they are pretty straight forward but the power is what confuses me as I know very little about Auto electrics. Any help or advice will be very gratefully received!

[Ferret]

Know nothing about relays like me? Read this:

http://www.bcae1.com/relays.htm

That's an amazing howto - excellent find - it's exactly what I was trying to describe! I *have* drawn up a quick diagram but it's pretty much identical to the better drawn diagram in that desc!

For a suitable relay have a look at : maplins (http://www.maplin.co.uk/Module.aspx?ModuleNo=37526&criteria=automotive%20relay&doy=29m4)

Good value at a max of £3 - and you can pick up wire and crimp tools to do your jobs there too :) If I'm in the area anytime soon I'll give you a hand with it if you want!

[leicesterboy15]

Thanks Ferret, I hope dinner was nice :) !!

I think I get what you mean but a diagram or any web links would be very handy.

And why do I need a Relay? You're scaring me now, and I don't think a bus would fit under the rear seat :)

[pingu]

What Ferret is getting at is that instead of trying to run +12V from the front of the car to the back of the car, you're better off connecting the various devices through a fuse and a relay directly to the battery (which is under the rear seat).

The "remote" signal from the head unit will go to +12V to turn on all the other devices, although the remote signal itself isn't strong enough to directly power all the other devices. So you use the remote signal to switch on a high current (e.g. 40A) relay: the various other devices are then connected to the battery via the relay.

When you turn your head unit off, the other devices won't draw power as the remote signal will drop back down to 0v, turning the relay off.

[leicesterboy15]

Ahh I see, exactly what I want! However I have no experience with relays, is there a certain type I need? Is there one I can buy off the shelf for this purpose?

[leicesterboy15]

Know nothing about relays like me? Read this:

http://www.bcae1.com/relays.htm

[leicesterboy15]

A visit from THE Ferret, that is an offer I can't refuse! No seriously, it would be nice to meet someone off the board! These things are easy with a bit of experience but can be scary when you don't have any! So I take it I need a relay holder for this? Are all the relay output points the same for all standard relays (as in the relay link I posted)? Will the remote on lead provide enough power to the relay? Thanks guys for all your help on this by the way and sorry if these questions sound stupid!

[gmannino]

The diagrams in the link are for a standard automotive relay. You want to find one similar and this should be pretty easy. The remote out from the radio will provide enough power to trip the relay.

I would run all your accessory equipment (Alpine brain, etc) under the back seat. Running all the cables to the rear might be lots of work and have more potential for noise. Although, under the seat can be just as noisy.

I have also places brains under drivers seats and under the foot well of the passenger side. I've even installed brains inside the dash, but e34's do not have enough room to do this.

[leicesterboy15]

Thanks for the info guys and sorry to resurrect this but I have started the install now and have a few more question s. My remote turn on lead comes from the brain which will be in the boot so I have to take power from the HU to the brain at the back, then the remote cable will go from there to the relay under the rear seat. The relay will be fed from the battery through a 30a fuse and head back to the rear of the car to a splitter chocolate box (or similar) to split out to all devices.

Is this the best way to do it? Is 30a correct? What gauge wire should the power cable be from the battery to the relay then from the relay to the splitter? Is a chocolate box OK as a power splitter or is there a better option? Any other recommendations are very welcome, I am open to all suggestions! Feel free to rip my planning apart!

[gmannino]

Once your run your remote turn on lead from your brain in the trunk, you can feed power to the relay via a 12 gauge or similar wire. There is not much current in the remote turn on circuit so dont worry about running a large cable. A 12 gauge or 10 gauge wire would be fine. Are you installing a 30amp fuse? if so, that seems kind of large.

If you are tapping from another fuse, then 30a should be OK. You do not need to run power directly from the battery and an ignition source should be OK.

I have no idea what a chocolate box is.

[leicesterboy15]

I have no idea what a chocolate box is.

Ha Ha LOL!! I'm not aure how to explain it either! Only reason I'm installing a 30a fuse is because I have one from an amp wiring kit and because the relays are rated at 30 or 40 amps but I will go lower if recommended. Is it better not to take power directly from the battery? When I used the power cable to the brain last time it seemed to run out as the whole stereo would cut out if the volume went up or the bass kicked in

[gmannino]

If you are having issue as mentioned above with the stereo cut out, it could be a loose or bad ground on the subwoofer amp. The head unit and brain take very little current.

hundreds of times I have ran both the stereo, brain and all accessories off of the factory radio harness without any issues as long as the fuse rating matches the added equipment.