I want to run a wire straight from the battery to an audio amplifier that's going inside one of my rear storage boxes. This is an XJSC with no rear seats - rather, it has storage boxes instead.

What's the easiest way to route it?

 

The safest way is to take the power from one of the firewall posts. These serve BOTH sides of the firewall, but to get to the inside side, it is a dash out job!
How much power do the amps need? There are pretty thick brown wires that come from the firewall posts inside to the ignition switch, for example, that will probably give you enough current. The you can just run the cable under the console to the rear.
Greg

 

I've got some split loom electrical conduit, and will fuse the wire at the battery, so it's going to be pretty safe. I have a boat, so do auto wiring to marine (ABYC) standards, which are the strictest, after aircraft.

I don't like the idea of taking the dashboard out! Can either side be reached without doing so?

 

Isn't the battery in the Boot/trunk? if so, and you just want to run a large gauge hot wire (fused) to the amp, can't you just drill or find an occupied wire bundle through the rear trunk/cabin bulkhead?

 

Yes, that's the plan, but I thought someone might have done the same thing before.

 

I installed an amp in the boot/trunk of a facelift convertible which had the rear cubby rather than rear seats, and then ran multiple speakers wires from the boot into the cabin. The design may be similar enough to your XJ-SC.

In researching it, I came across some posts that said you can run the wires from inside the boot through a cavity over the wheel well and into the cabin.There is supposedly some foam there that you can can poke through with a wire hanger or such. I wasn't able to get that to work although I can't remember exactly why. You could try that first.

In the convertible there is a parcel shelf behind the cubby that is covered with carbet. I drilled a small hole in the rear corner of the parcel shelf, under the carpet. This provides access to the boot just aft of the fuel tank. I drilled from the trunk to the cabin to make sure not to hit the tank. I used some tin snips or similar to open the whole to about 1/2" round, then ran the wires from the amp in the boot through that hole and along the side of the parcel shelf (under the carpet still).

I used a rubber grommet at the hole around the wires and a little silicone seal to seal it up. It did involve cutting that hole as noted, but I never had any problems and it was concealed by the carpet.

I forgot to add that I removed the cubby when doing this to route the wires where I wanted them to go once I had them in the cabin.

 

Thanks for the reply, that's very interesting info.

 

I also tried to feed wires over the wheel well and failed.

 

Yes, as I mentioned, if you look behind the ignition switch at the loom attached to it by a plug, you will find a very large diameter 12 volt brown wire. This can then easily be run rearwards under the console and carpets, where, if you have ABS, you will find the ABS wiring.


What sort of amperage do you need?
Greg

 

Hi Greg, need 30A. The amp instructions say to use 10 gauge wire.

 

A dedicated wire needed then!
If you remove the RHS boot side trim, and the RHS rear trim on the cabin side aft of the door, you can shove a flexible probe right round the wheel arch inner into the cabin. If you use an extra outer protector on the cable such as a silicone or polythene reinforced tube you thread the wire through, as chafing is a possibility, I think that would be a good solution.
The LHS has OEM a bundle of cables going through a dedicated pathway, basically this route, but that would require a cable across the boot floor past all the fuel tank and pipes, which I think would not be a great plan.
Greg

 

Thanks for the info! I'm just waiting for a spool of wire in the mail, then I'll have a go. I'll let you know what I end up doing.

 

Electricians that work on buildings make use of a flexible,. yet stiff probe to feed the wires through conduit and closed spaces.


I think a piece of weld rod, the thin guage or wire coat hanger, if they still exist, would do it so long as the distance is in range.


Caveat, neither audio or electrics are my strong suite. Yet, I've managed some installation of each kind.


Right now, audio in my head is muted. DR. gave me some prescriptions to clear the tubes.


Although a quiet world is kinda nice.





Carl

 

30amps wow, you obviously have a convertible. I have a Class A 20watt amp with 90dB speakers and can't turn the volume past 1/2 way and stay in the car.

Anyway back to your question there are 2 grommets that pass wiring from the boot to the cabin. They are behind back seat back on the left and right corners, I would imagine they are in the same place. For feeding wires I use a plastic tong from particle board flooring, its flexible but stiff enough. If you run the wiring over the inner wheel arch make sure it's in conduit or it will rub the insulation.

 

The idea is to put two 6.5" bass speakers in the rear lockers (making new lids so I don't have to deface the irreplaceable stock ones) and drive them with a class D amplifier (150 wpc in bridged mode), making a sort of subwoofer. The standard speakers do go plenty loud enough with the 20W from the head unit, but when you try and make them produce too much bass, they distort. So this way the door speakers won't be expected to make much bass. I am not a bass freak, just trying to get a good balanced sound.

 

My 20watt amp drives 2 6.5" 8ohm bass speakers which are 90dB so don't need that much power to get SPL. Front speaker are driven directly from the head unit.

I used 2 of these. They are brilliant little bass drivers for a car and very low in distortion. If you have'nt bought the speaker might want to consider these and this will reduce your power needs.
https://www.jaycar.com.au/6-5-paper-...range/p/CW2194

Power is a useless measure in audio for how loud a system will play, Sensitivity of the speakers, specified as XdB 1watt@1m. The bigger the dB number the less power needed to get volume from the speaker. Each 3dB doubles the power needed.

So a speaker rated at 80dB would need 80watts to make the same noise as a 92dB speaker with 5watts

 

Good point Warrjon. I forgot that the main ECU to engine loom goes through to the cabin on the RHS. I am sure that with a stiff nylon fishline (google it, used for pulling cables though trunking) the OP could get his cable though that path. Just as long as the current/magnetic effect would not foul up those delicate ECU signals from the engine sensors?

 

No it won't because it's DC, if it was high current AC then that could cause issues with sensors.

 

It might be mostly DC, but you could expect some fluctuation as the amplifier outputs AC. Depends how much capacitance it has internally. If it is drawing on the 30A cable to produce 300W of 50 hz bass, it is not hard to imagine some AC component in the current draw.

 

Been thinking about this and what you are trying to achieve. Bass is the hardest thing to get right and it depends on what you want vibrating rumble or tight clean bass.

If you are looking for deep bass that rumbles the car then you need BIG speakers to move a LOT of air. I would look at 10" as a minimum, there are a lot of good cheap 10" woofers out there with SPL around 89dB.

This speaker SPL is 92dB 1watt@1m and for each 3dB a speaker is lower in SPL you need double the power for the same reprieved loudness. So if you are driving the 93dB speaker with 5watts (you would need a 20watt amp to allow for transient response).

To drive an 83dB speaker at the same loudness you would need 40watts and a 160watt amp

http://www.ebay.com.au/itm/Woofer-Po...sAAOSwT6pV1DpG

If like me you prefer tight bass where you can hear pop of the drum, then this is primarily delivered in the mid to upper midrange. But you need to crossover and phasing correct or you will not hear this tight bass.