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      01-11-2013, 12:07 PM   #1
ellipsis212
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Tips on routing 4 AWG cable from battery to amp

I've seen loads of pictures over the last week of people's completed and in-progress installs, and I'm going ahead with adding a sub/amp to my 330i.

Last night I poked around in the trunk for a bit trying to determine the best way to route my power and ground cables without upsetting the trunk carpeting. I'm pretty intent on making sure the trunk floor sits flush and with 4 AWG cables, it seems to be a little tougher than I was expecting as the carpet panels are extremely stiff.

Before I stare at it any more, does anyone have any default routes for amp cables? The amp is in the under-floor bin.

Thanks for any advice. My preference is to do no cutting.
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      01-11-2013, 12:26 PM   #2
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Over the fender well across under the trunk floor where the TCU and
or other optional electronics modules are stored Back over the other Fender
Well to the battery. If you want a picture look in here .

http://www.e90post.com/forums/attach...3&d=1329017429

There are plenty of pictures in other install threads also .

http://www.e90post.com/forums/showthread.php?t=641323

You don't ever want to do cutting .
I have read plenty of intstall threads and only those that
are fabbing entire sections ever do that and rarely do that.
What are you putting it in?
Since I am assuming you are putting in an amp that fits in the
stock location.

http://www.e90post.com/forums/showthread.php?t=324214

I think he does break out some ribs for this.

Last edited by ctuna; 01-11-2013 at 12:38 PM.
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      01-11-2013, 01:07 PM   #3
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Thanks ctuna, that E91 build sheet was helpful. I've combed through so many threads but search parameters are just so generic. Looks like I'll try going over the strut tower and into the rear corner. I'm sure it'll look flush once I've reassembled the trunk.

The amp is going in the under floor bin. It's a mono amp just to drive the sub and I already hooked up the Technic harness and ran rca's and remote lead. I'm really pining for an integrated fiberglass enclosure for the sub but I'll probably try my hand at fabricating one since they seem to be going for a pretty penny (when available, that is).
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      01-11-2013, 09:22 PM   #4
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Why 4 gauge? 8 gauge should be enough unless you're running more than a kilowatt.
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      01-12-2013, 08:36 AM   #5
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I ran mine up over top of the trunk
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      01-14-2013, 11:05 AM   #6
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Quote:
Originally Posted by kaigoss69 View Post
Why 4 gauge? 8 gauge should be enough unless you're running more than a kilowatt.
I bought a second hand setup and that's what it came with, so I'm just making it work rather than buying new cable and fuse block. The amp is 600w rms so I suppose it can't hurt.

Finished running cable on Saturday based on the above picture. The 4 guage cables just barely fit without upsetting the floor more than a couple mm. If I asked a casual observer if the trunk floor was flush they would say yes.
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      01-14-2013, 11:31 AM   #7
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One more question: is there any objection to using the right rear fender arch ground point as opposed to the left? I've seen several instances of people using the left side, but my guess is that's just because they have their amps on the left side whereas mine is in the center?

The vehicle electrical pdf doesn't mention a difference between the two factory grounding points.
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      01-14-2013, 12:04 PM   #8
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My ground runs right to the batttery lug.

My ground runs right to the battery lug.
I have been told its less noisy. Other people use the ground points on the
Fender Wells . It goes to the tightening bolt on the battery clamp. Whatever you do measure the resistance to the top of the battery before you fire it up.
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      01-14-2013, 02:40 PM   #9
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Quote:
Originally Posted by ctuna View Post
Whatever you do measure the resistance to the top of the battery before you fire it up.
That sounds serious. Is that for noise reduction, ground safety, or both? Do you just use a multimeter and look for voltage drop?

While I've installed a few amps in previous vehicles I've never actually tested my ground point. I just used whatever other folks with the same vehicle recommended.

Also, I could've grounded to the battery directly but the ground cable would've been like 7' long. Is that an issue?
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      01-14-2013, 04:11 PM   #10
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It's probably better to use the chassis ground than wire directly to the battery. BMW uses lots of wires coming off the positive terminal for various purposes and power save modes. The biggest is for the starter/alternator, then there are 2-3 smaller fused and switched lines which will turn on or off for various power modes (on, sleep, standby, ignite, etc etc).

On the other hand, there's only ONE coming off the negative terminal which then connects to the chassis. That run has a current sensor in it to monitor battery state of charge. If you have a ground connection that bypasses that, you could very easily end up with a situation where the car gets confused about whether the battery is full or empty, and doesn't charge it appropriately.

Of course, for HUGE setups, you might want to run another ground cable for the sake of current handling, but then that ground lug handles 1kA during starting anyway, and it's not like you're putting in a more powerful alternator. So again, probably best if you don't.

Additionally, it's generally better to avoid adding ground lines anywhere you can to avoid creating ground loops. Create too many paths for ground current and you can couple unforeseen noise in. Same way you can get weird effects if you have your phone plugged into aux and a crappy charger at the same time in some cars.
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      01-14-2013, 06:04 PM   #11
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The long ground cable I have

The long ground cable I have comes with a professional kit that one of the
better known vendors on this board supply's. I see a lot of people use the nearest ground point and a few of them are having noise problems.
I measure everything before I apply power. If you are using a chassis ground I would take a resistance check on it to make sure it was very low meaning that if I short the leads of the meter together nothing is added ohms wise to the measurement when going from the ground point to the negative terminal on the battery .(sub tracking out the ohm value of the test leads is what
I'm getting at )
I ran across a guy that had just tried to attach it under the nearest bolt, but the chassis had anodizing there giving him a high resistance connection
and he was blowing the inline amp fuses right and left till somebody told to him sand down the connection point.

Another way to check is measure the battery at the terminals
of the battery and then again at the amp power terminals the voltage should be very close should be very close if you have a good connection.(with the amp on)

Last edited by ctuna; 01-15-2013 at 11:58 AM.
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      01-15-2013, 10:12 AM   #12
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great info, thank you.
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      03-05-2013, 01:20 PM   #13
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Quote:
Originally Posted by alexwhittemore View Post
It's probably better to use the chassis ground than wire directly to the battery. BMW uses lots of wires coming off the positive terminal for various purposes and power save modes. The biggest is for the starter/alternator, then there are 2-3 smaller fused and switched lines which will turn on or off for various power modes (on, sleep, standby, ignite, etc etc).

On the other hand, there's only ONE coming off the negative terminal which then connects to the chassis. That run has a current sensor in it to monitor battery state of charge. If you have a ground connection that bypasses that, you could very easily end up with a situation where the car gets confused about whether the battery is full or empty, and doesn't charge it appropriately.

Of course, for HUGE setups, you might want to run another ground cable for the sake of current handling, but then that ground lug handles 1kA during starting anyway, and it's not like you're putting in a more powerful alternator. So again, probably best if you don't.

Additionally, it's generally better to avoid adding ground lines anywhere you can to avoid creating ground loops. Create too many paths for ground current and you can couple unforeseen noise in. Same way you can get weird effects if you have your phone plugged into aux and a crappy charger at the same time in some cars.
This is great advice, maybe why I am getting an SES code 4A66 on my electrical management system. I am moving my ground.

Now, I am looking to improve my power connection which is straight to the nut holding the battery clamp on the positive terminal. This is pretty crude but effective. However I would like to use the MAK8 plugs which are part of the big red terminal adapter pictured below. But I have only two gray sockets left available on the right side and they have funny colored dots on top of them. If I split my power cable into two MAK8 connectors and connect to these available ports, could there be any problems? Does that big red BMW terminal adapter have fuses in it?
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      03-05-2013, 02:25 PM   #14
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When you use the top of the Fuse Block

When you use the top of the Fuse Block on top of the battery you have to check that there are fusible link blades in the slots you are thinking about using.
Some cars come without fusible link blades in some of the slots.
I would just as soon bypass the fusible link connection points . If you blow them you have to replace the whole fusible link assembly .
The links have different capacity's I think there is a picture some where with the actual amp ratings for each one.
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      03-05-2013, 02:27 PM   #15
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Quote:
Originally Posted by Quasimodem View Post
This is great advice, maybe why I am getting an SES code 4A66 on my electrical management system. I am moving my ground.

Now, I am looking to improve my power connection which is straight to the nut holding the battery clamp on the positive terminal. This is pretty crude but effective. However I would like to use the MAK8 plugs which are part of the big red terminal adapter pictured below. But I have only two gray sockets left available on the right side and they have funny colored dots on top of them. If I split my power cable into two MAK8 connectors and connect to these available ports, could there be any problems? Does that big red BMW terminal adapter have fuses in it?
I do believe it does, yes. That's the idea behind the multiple cables - the main starter/alternator cable is not fused. You'd have to fuse it at north of 1kA, and 1kA is effectively a short circuit anyway so from a safety perspective, if the cable got cut in a crash, the fuse probably wouldn't blow and you'd still get dangerous sparks or current either way. Hence the explosive disconnect when you get in a crash. Safety thing. The others are all fused much lower than shor circuit current, though, so you don't need some kind of disconnect.

The question is, what ARE they fused at? I couldn't tell you, maybe look it up in WDS?

Aside, where can I get MAK8 plugs? I have some other always-on aux systems I'd like to plug in that way for cleanliness, but never figured out what connector it was (thanks for mentioning it!)



Ahh, here you go for fuse ratings on the distribution block.

There are some 100s, an 80, and a 50A terminal, so if you're smart about which amp goes to which, and you include an appropriate and lower inline fuse after, you can definitely use them.

Last edited by alexwhittemore; 03-05-2013 at 02:33 PM.
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      03-05-2013, 10:03 PM   #16
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Quote:
Originally Posted by alexwhittemore View Post
I do believe it does, yes. That's the idea behind the multiple cables - the main starter/alternator cable is not fused. You'd have to fuse it at north of 1kA, and 1kA is effectively a short circuit anyway so from a safety perspective, if the cable got cut in a crash, the fuse probably wouldn't blow and you'd still get dangerous sparks or current either way. Hence the explosive disconnect when you get in a crash. Safety thing. The others are all fused much lower than shor circuit current, though, so you don't need some kind of disconnect.

The question is, what ARE they fused at? I couldn't tell you, maybe look it up in WDS?

Aside, where can I get MAK8 plugs? I have some other always-on aux systems I'd like to plug in that way for cleanliness, but never figured out what connector it was (thanks for mentioning it!)

P.S. That link to Taibanl's list of the distribution block amp ratings for the fuses may be reversed. He said it was "inboard to outboard" and the last one is hardwired. That would make the far right one hardwired, but the left one appears to have no fuse in it and it appears to be merely a part of the plate which would then be "hardwired" right? But the right one does appear to be the largest. So I am a bit confused.



Ahh, here you go for fuse ratings on the distribution block.

There are some 100s, an 80, and a 50A terminal, so if you're smart about which amp goes to which, and you include an appropriate and lower inline fuse after, you can definitely use them.
The part numbers are in Dannyboy's post just below this one (or try http://www.e90post.com/forums/showthread.php?t=794560) I believe they are MAK8 connectors, I think I got that from realoem.com when I looked up the part numbers Dannyboy posted. I found some information about them on the LEAR website: http://www.lear.com/en/electrical/te...onnectors.aspx. Yeah, I guess I am going to have to pull that red positive adapter module and look into it before I start plugging into it. I dont need a fused connector as my power line already has a fuse in it.
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      03-05-2013, 10:14 PM   #17
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Thanks! I'll have to give my local dealer a call and see if they have them for similar price. I was half expecting it to be something outrageous like $15 :P

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I dont need a fused connector as my power line already has a fuse in it.
Well, true, but more fusing is better than less. Plus, those contacts can't be rated for much more than the 100A the biggest terminals are fused at. Even 100A seems unbelievably high for that connector.

Anyway, pick a terminal with more current than you need and you'll be fine. You may even have a free hardwire at the end.
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