Where to get power wire from 911 SC battery into the cabin?

[NickW21]

I've got a '79 911SC Targa and am in the process of installing an amplifier and powered sub underneath the two front seats. My plan is to take power directly from the battery with an in-line fuse, then connect to a distributor with two power lines going to the amp and the sub. I am having a hard time finding where to snake in the power wires from the frunk into the cabin. I've read some threads, but I cannot determine from them exactly how/where to do this. Anyone that has done this on the SC model that give me some help? Pictures would be awesome if you have them.

Also, once I get the power to the amp and sub, can I just use the seat mounts for the grounds?

[kimlangley7]

I'm busy right now - I have some pix of my set-up.. and some questions > I'll be back

kgl

[mrrolleyes]

Check in front of your passenger footwell. My battery is in the smugglers box and I have a holy from old ac for direct access.

Here is my under seat. I tapped ground to the side of the seat mounts.

[NickW21]

I am installing that same sub. I have a single power line running into the cabin. Got that to work as folks have said, through a hole that was plugged under the passenger side of dash. Then I have a power distributor with 2 lines going out, one to the sub and one to the amp. However, I’m not getting the proper power to either component. I’m wondering if it’s the power distributor that is the problem. I got a one (up to 3) in and then 3 out. I’m not using the middle out and only have 1 of the 3 lines going in. Could this be causing an issue? Also, I have grounded both pieces to the nut holding in the emergency break case. So, maybe that isn’t the proper grounding? I’ll post some pics of the setup shortly.

[NickW21]

Here are some pics of the touchpoints I referenced above...

[NickW21]

One other item that could be problematic. I have a Blaupunkt Toronto 420 BT head unit that came with the car when purchased. It has an Remote out option, but no connector cable with it. So, I'm using the ignition switch line for the radio ignition switch as well as the remote lines for the amp and sub. The radio still turns on in this way, and I get some power to the amp, but the amp protection light is on meaning that there is something wrong with the electrical setup and there is no power at all in the sub Any notable areas that I have misconfigured, please let me know. I'll continue to troubleshoot in the meantime!

[75 911s]

As a test, run a beefy ground cable to the battery ground post.

[NickW21]

Originally Posted by 75 911s

As a test, run a beefy ground cable to the battery ground post.

You mean, all the way to the battery terminal (-)?

[FrankM_]

Or any of the ground points. In my car the rails are painted and not good ground points. I ran a 6 mm2 ground from the underseat sub to a ground point behind the passenger floorboard (a screw through the sheet). And off course a 6mm2 direct power (fused) from the battery plus.

I don’t think using the contact (acc) as ‘remote in’ is wrong. The sub doesn’t draw power from that line.


Sent from my iPhone using Tapatalk

[FrankM_]

This post seems to have the ground points for the SC

Location of ground straps


Sent from my iPhone using Tapatalk

[Tremelune]

I ran power into my 1970 from the starter (which is closer to the alternator). I ran a 4awg line through a hole by the transmission tunnel, then up through a hole near the handbrake.

Be sure to fuse the thing before it gets near anything metal; the closer to the source the better. Grommets (or just a piece of plastic hose ziptied around) are a very good idea where it bends near metal or enters/exits a hole.

[Tremelune]

Originally Posted by NickW21

Here are some pics of the touchpoints I referenced above...

It's not likely that this cable will rub against the gas tank and short, but if it did it would be in about the worst place it possibly could...

If it were me, I'd make sure the fuse was closer to the battery, before the cable can touch anything.

[Tremelune]

Originally Posted by NickW21

Then I have a power distributor with 2 lines going out, one to the sub and one to the amp. However, I’m not getting the proper power to either component. I’m wondering if it’s the power distributor that is the problem.

Check the fuses in your power distributor. A test light will be handy for figuring out where you're losing the connection.

Your amps should at least power on and show some lights even if the ground is of low-quality. I suspect the handbrake is a good ground, but scraping the paint off the chassis underneath that bolt would make it an excellent ground.

[Coastr]

To answer your question there are some grommets that come into the dash behind the glovebox area. Pop the grommet out, push the wire through and put the grommet back in. Depends on how big the power wire is, but did this recently with some half decent power cable and it worked ok.

[creaturecat]

can you not sneak it in thru heater control cable opening?

[NickW21]

HELP!!!

I really have no clue what the issue is. I've read articles, watched videos and it appears I have everything wired appropriately, but yet, it still does not work. Here's some more details:

1) I moved the in-line fuse closer to the battery terminal (just under the fuse box). This has a 60amp fuse in it

2) I scraped off the area around the screw for the e-brake to get to bare metal. Then, with a power wire connected to the (-) battery wire (not attached to the battery) and a digital multi-meter attached to that wire and the ground point and set to Ohms, I got 000 for a reading. This was a good reading from everything I've seen.

3) I then remove the wire from the battery harness and reconnect it to the (-) battery terminal

4) In-line fuse blows instantly

My amp is a 4x70W RMS class A/B, so that should yield about 40amp max. The amp in the powered sub is 125W RMS class D, so that should yield 12amp max. I've got a 40amp fuse on the power line coming from the distribution block to the amp and a 20amp fuse on the power line coming from the distribution block to the sub. Grounds from both the sub and the amp are attached to the same screw at the e-brake. Remote lines are attached to the ignition switch line.

Any ideas?

[Tremelune]

A 60A fuse popping instantly points to a short somewhere, and it's likely before the power distribution block, or one of those two fuses would likely have blown first. It's hard to blow fuses this large just by cranking the amp, and it can take several seconds or even minutes.

Make sure all your power wires have no damaged insulation and aren't touching anything metal, and thank your fuse's sacrifice for preventing a fire...Likely suspects are where it crosses the firewall, gas tank, or seat rails.

It's not clear why you're testing resistance. From your ground point (handbrake bolt) to the positive power wire you should have over 12V. So, black lead on the multimeter to handbrake, red lead to the power wire or distribution block or amp terminal, it'll read ~12.5V (if both battery terminals are connected, otherwise you have to run the black lead all the way to the battery, since the chassis is no longer grounded). What is a battery harness? Usually "power wire" refers to the 12V positive wire (as opposed to "ground wire", which connects to the negative).

Make sure you positives aren't connected to grounds and vice-versa...There have been times when I've only had red wire and used it for ground and forgot about it until I saw sparks...

Make sure your power distribution thing is only handling positive wires and doesn't touch ground at all.

[Tremelune]

This is probably nothing, but you have black and red terminals connected to ground by that handbrake bolt...They're both supposed to be grounds, right? I hate getting my colors mixed up, but sometimes you run out of one color, so I usually use electrical tape or shrink wrap to "correct" any mismatched colors...

[NickW21]

Originally Posted by Tremelune

This is probably nothing, but you have black and red terminals connected to ground by that handbrake bolt...They're both supposed to be grounds, right? I hate getting my colors mixed up, but sometimes you run out of one color, so I usually use electrical tape or shrink wrap to "correct" any mismatched colors...

Thanks for the help. Yah, that is a black, ground wire, but the only terminal I could find at ACE Hardware was a red one

In terms of testing resistance, I was using the ground battery terminal wire (not attached to the battery) to measure that my ground point was actually grounding. Any large resistance there would indicate that I need to find a better ground point. At least that's what I had read

I really have no clue where the short could be. I thought maybe within the in-line fuse, but ran tests on the fuse housing/etc. and that's not it. Did the same with the power distribution block (only power lines going in/out of this). I took out the 2nd line going to the sub all together and remove the corresponding fuse. Fuse instantly blew again.

I just examined the power wire going from other end of the inline fuse to the power distribution block and could see no insulation breaks. It passes through the firewall that has a rubber grommet in the hole, so I'm not sure what could be shorting it out in between. I've just reworked the wires at the battery power terminal to see if maybe some of those wires were causing a problem. I moved the amp power line from touching any other wires along the way (amp power wire terminal still touches the two existing terminals that were attached to the battery, but no wires touching after that). So, I'm going to try that with my last fuse and pray it doesn't blow immediately.

Any ideas on how to check for shorts prior to me simply testing it by hooking up the (-) battery terminal, seeing as I only have the 1 fuse left??

[3rd_gear_Ted]

Disconnect both wires to the amp and test the integrity of the power wiring first. Short circuit is in the wiring or the connected loads.
60A fuses blowing is not good, be careful