Viewing: Wiring

**Jakeymd** · 20-05-2010, 08:37 PM

I'm a bit of a newbie when it comes to this sort of stuff. I'm wiring an amp and a sub in the boot of my car. I need to get the power cable from the boot to the battery and i've got as far as the glovebox but can't find how to get through to the engine bay. I can't find any predrilled holes or grommets. Does anyone know where i can look or any other suggestions. There's not much room to drill a hole so that will be the last of my options if i need to. It's a 1999 Vauxhall Astra. Any help would be appreciated.

**pgarner** · 20-05-2010, 08:46 PM

have a look in the engine bay to see where the main wiring loom goes through the bulkhead

**Jakeymd** · 20-05-2010, 09:51 PM

Quote:

Originally Posted by pgarner

have a look in the engine bay to see where the main wiring loom goes through the bulkhead

I looked for this, but the all the wires are connected to a terminal within the bulkhead, then carry on out of the terminal on the otherside. So nowhere for it to go. It's a puzzle.

**turbonutter69** · 21-05-2010, 07:47 AM

Look under the bonnet and you should find some wires going through the bulkhead.
If I was doing it I would of started feeding the wire from front to back.

***T9 man*** · 21-05-2010, 08:20 AM

Try the drivers side above the pedals, far right hand side, and between 300 and 400mm up measured from the floor, you should see some exit point grommets there. No drilling is required here if you are only pulling in an earth and battery feed. I would then try as turbonutter69 has already suggested to you, to run the cables from the engine bay first and then run the cables towards the rear of the car, some people find that a lot easier and minimises errors by pulling in cables that otherwise might end up short of the mark. Also, Subs are prone to induced hum, so use a good quality screened cable for the low level signal in, and try to keep the signal feed away from the battery feed by keeping as much distance as possible between them, I tend to run power down one side of the car and signal cables down the otherside, Good luck

**turbonutter69** · 21-05-2010, 08:24 AM

Yeah remember to run the RCA cables the opposite side to the power cable.
Also remember you only need a power feed from the battery earth the amp to the boot floor.

**BAD63R** · 21-05-2010, 08:33 AM

Pop ya bonnet and look towards the back on the battery side. You will see where the brake lines go through the bulk head. Next to that should be a gromit with a thick load of cables, snip the gromit to the middle on one side, then just slide the amp cable through. It should appear high up in the passanger footwell, then just pull through what you need to get to the boot. When finished just takea nice bit of clear silicone and give the gromit a fresh seal. Jobs a good'n.

***HDi fun*** · 21-05-2010, 11:38 AM

Quote:

Originally Posted by T9 man

Try the drivers side above the pedals, far right hand side, and between 300 and 400mm up measured from the floor, you should see some exit point grommets there. No drilling is required here if you are only pulling in an earth and battery feed. I would then try as turbonutter69 has already suggested to you, to run the cables from the engine bay first and then run the cables towards the rear of the car, some people find that a lot easier and minimises errors by pulling in cables that otherwise might end up short of the mark. Also, Subs are prone to induced hum, so use a good quality screened cable for the low level signal in, and try to keep the signal feed away from the battery feed by keeping as much distance as possible between them, I tend to run power down one side of the car and signal cables down the otherside, Good luck

Whare does the hum emanante from - the car's supply is a DC rail.

***T9 man*** · 21-05-2010, 12:05 PM

Will try to make this brief and hopefully straight forward. The hum is caused by the deterioration of the margin voltage caused by variations in the DC power supply which does have a slight AC ripple in the line voltage through the bridge rectifier and smoothing capacitors, which produces an electromagnetic interference (EMI), to the corresponding power induced in a conducting wire antenna (CWA). DC voltages in the electrode circuit in magnetic-conductive flow measurement with periodically reversed DC magnetic field in which the useful signal is obtained by sampling and storing the signal voltage after each reversal of the magnetic field at opposite polarity values of the magnetic field during a sampling time interval and forming the difference of the stored sampled values, and wherein in a compensating time interval following each sampling time interval a compensation voltage is produced by sampling and storing the signal voltage, which compensation voltage is superimposed oppositely on the signal voltage for compensating the signal voltage within the compensation time interval to the value zero and is retained until the next compensation time interval, wherein each compensation time interval lies within the time interval corresponding to the switched-on magnetic field.

***HDi fun*** · 22-05-2010, 11:21 AM

I would have thought that HF switching noise from the PSU is more likely to cause interference. Switched mode power supplies do not require bridge rectifiers unless the input supply is AC.

Even then it's more likely to be picked up electrically than electromagnetically. What you're discussing sems more relevant to a transmission line.

If the impedance of the HU's sub output is sufficiently low this should damp out any low frequency EMI. Also if the internal resistance of the supply is low and the supply rail 'stiff' enough I cannot see how EMI can occur.

Your point about hum is not exclusive to sub-woofers. It's jst that subs are more likely to have the necessary frequency response to reproduce it audibly.

**Jakeymd** · 24-05-2010, 10:49 AM

Okay, so my dad suggested taking it through the bottom of the boot and running it underneath the car. Is this a good idea??

**pgarner** · 24-05-2010, 12:59 PM

as long as its sequred properly and sealed.
i would advise using armoured cable rather than the normal stuff however.

does your car have electronic throttle (DBW)?
just a thought if it does you may find that there is still a grommet in place for a throttle cable

Edit: you may have to pull the carpet back to find it

***HDi fun*** · 24-05-2010, 01:25 PM

Quote:

Originally Posted by pgarner

as long as its sequred properly and sealed.
i would advise using armoured cable rather than the normal stuff however.

does your car have electronic throttle (DBW)?
just a thought if it does you may find that there is still a grommet in place for a throttle cable

Very clever!

**Jakeymd** · 24-05-2010, 04:14 PM

I finally done it. Decided just to drill a hole. But now my amp still won't work. Not sure if i've got the remote cable right. My head unit doesn't turn on when the ignition is turned on, and i have to turn it on manually, could that have anything to do with it. My mate is coming round in a bit so i can check that the amp works on his wiring in his car. Any other quick solutions i can try? And just to make sure, which terminal does the power cable go onto?

***HDi fun*** · 24-05-2010, 04:47 PM

Quote:

Originally Posted by Jakeymd

I finally done it. Decided just to drill a hole. But now my amp still won't work. Not sure if i've got the remote cable right. My head unit doesn't turn on when the ignition is turned on, and i have to turn it on manually, could that have anything to do with it. My mate is coming round in a bit so i can check that the amp works on his wiring in his car. Any other quick solutions i can try? And just to make sure, which terminal does the power cable go onto?

The switched feed is only to make sure it goes off when the ignition is switched OFF. Manual switch on is absolutely normal.

WHcih power cable are you asking about?

I would still consider a separate earth to the power amps - you'll get a better bond than by using the car's -ve earthed bodywork.

**turbonutter69** · 24-05-2010, 05:32 PM

Have a read of this buddy. http://www.torquecars.com/forums/f10...ling-amp-8035/

**pgarner** · 24-05-2010, 07:06 PM

when the headunit is on it switches the remote wire to live

get a short length of wire and connect it from the +ve terminal to the remote terminal (make sure you disconnect the remote wire 1st

) this will supply power through the remote terminal to switch it on

**Jakeymd** · 24-05-2010, 08:14 PM

It's working now, pretty much. Except the remote wire. Because it doesn't work to my head unit, it's not going to work to my amp. So i connected the remote wire to the power cable. I have to take it on and off so it doesn't drain my battery but eventually i'll put a switch in. If i can get the remote wire working to the head unit then it'd be alot better. Any ideas?
P.S The sound is brill.

**pgarner** · 24-05-2010, 08:44 PM

check the head units settings, mines has an option for sub on off. with it switched off i dont think powers the remote line.

remove your head unit and find which wire is the switched live (ignition live) and tap the remote lead into it.

does your head unit switch itself off with the ignition ? if not then you may want to change the red and yellow power cables on the back of the head unit. although the are ISO (international standard) there are some that have permanent and switched lives the other way around. this is why most after market headunits will have connectors on the 2 wires to swap them about

**Jakeymd** · 24-05-2010, 09:59 PM

The head unit doesn't switch itself off when the ignition is off. Replacing the wires sounds like a big job. Think i might just get a switch for the remote cable. Not perfect as i'll most likely forget to switch it off, but it must be alot easier.

**pgarner** · 24-05-2010, 10:22 PM

nope its a 2 min job.
remove headunit
locate the red and yellow wires and swap them

mulitmeter on the 2 wires to find what one is ignition, if its not written on it
cut the ignition wire
strip both ends (make sure the ignition is off)
wrap the remote wire into one end of the wire
add a terminal block ( 5 amp one will do cost about 50p for a strip of 12 from a decent hardware store)
put the other half of the wire in the other side
tighten up both screws
wrap in insulating tape - for additional protection

**Jakeymd** · 26-05-2010, 06:55 PM

I'll give it a try. Cheers

**Jakeymd** · 26-05-2010, 08:33 PM

Finished. Everything is working perfectly now. I didn't have to change any wires around. I just found which wire worked with the ignition on, and that didn't work with the ignition off. Turned out to be a really thin blue wire with a red stripe. Figures. Thanks for the help everyone.

**pgarner** · 27-05-2010, 04:00 PM

blue wire is normally the remote line

**Jakeymd** · 27-05-2010, 04:48 PM

I thought that, so when i saw it had a red stripe i dismissed it. But there we go. It's all done now.