trunk mounted battery

[billpatterson]

Hi there

'Ohmess' provided me a response for his E9 (Thank you!). Since I don't know if the battery-starter-charging circuit of the E9 is different than the E3, I thought I'd ask the same question of the E3'ers out there.

Ohmess's reply was,
I ran a positive cable from the battery to a large marine distribution block in the engine bay, connecting starter power, alternator charging, and all other unswitched power off the distribution block.

So...I am moving the battery to the trunk of my '73 bavaria. I like the additional space a distribution block vs a battery provides that corner of the car. I use a battery tray bolted to the back panel.

As I recall...when I moved the battery to the trunk on a '71 2002 resto, the car only needed the + battery wire run to the engine bay (to the distribution block), then to the starter and connected the alternator to the distribution block). I grounded the battery under the rear seat. And...on a Land Rover II 109 resto I moved the battery to under the drivers seat; in addition to the + from the battery to the alternator, this vehicle needed a charging wire from the alternator back to the positive on the battery.

On a '73 bavaria, is a + charging wire that is run from the alternator back to the battery needed?

Any direction, advice, learnings, pics are appreciated.

Regards,
Bill

 

[Mike Goble]

" in addition to the + from the battery to the alternator, this vehicle needed a charging wire from the alternator back to the positive on the battery"
That would be the same wire...
You can connect your charging wire anywhere on the battery cable because the entire cable is electrically the same point as the battery+.
I have rear mounted batteries and use the battery cables from an E30. There is one large cable that runs along the passenger side to a junction box on the firewall with a single large stud. From this junction box a large cable is routed to the starter, and another small cable to a smaller box, which is my main power distribution point. This wire is protected by a fusible link. From this smaller box my 12v power is distributed to the fuse box, fan, MSD ignition, etc. and has a short 8 gauge wire to the alternator.

 

[Ohmess]

Yes, good idea. Let's bring this conversation onto the forum. As noted in my email, I ran a welding cable from the battery in the trunk to a marine distribution block on the battery tray. Run went through the frame rail on the passenger side (opening up the cover in front of the passenger front seat), and across the nose of the car to the distribution block so as to avoid punching a hole in the firewall. Battery was grounded to the body in the trunk.

At the distribution block, I connected the welding cable to the starter, alternator and other unswitched power.

I was not entirely happy with the way I had the battery held down in the trunk, (using a strap through the wood floor). I had originally thought I might install one of those battery/rear strut brace combination things, but there were two problems. The elephant skin in my trunk is in good shape and I did not want to mess it up. Also, I did not want to drill holes in the sides of the strut towers to do the install (I'm generally reluctant to introduce new holes into my car). I also wanted to relocate the distribution block on the battery tray to a more discrete location, but hadn't yet found one.

And, around this same time I acquired the triple Weber sidedraft setup, which became a higher priority. So, I reversed my setup, bought a new battery to starter cable and installed an optima red top battery.

 

[m5bb]

Moved my battery to trunk. Ran properly sized cable down passenger side and through firewall at cavity next to wiper motor (passenger) and installed an E46 connection box there that you can hook jumper cable to if necessary and have to go in trunk. + cable then goes along firewall down to terminal beneath power steering res. Then + power goes to starter etc. Ground cable in trunk connected to body with 8mm bolt and lock nut. Made sure it was a really good ground. So far ok.
Also have small fuse box in trunk for e28 window motors with 10ga wire and power for fuel pump (which is great as I can pull the fuse if I want key on). Power for amps under rear seat as well.

 

[billpatterson]

Thank you all for the replies. Thank you Ohmess for being patient with my enquiries. I do not pretend to understand electrics; that has gotten me in trouble. Ands thanks to these Forums; we all have a wealth of knowledge and experience handy.

Your descriptions all make sense. Don't know why I am having trouble with this concept this time. I think restoring the '80 Land Rover II 109 corrupted a few of my primarily pre '74 BMW resto files. What an archaic vehicle, compared to older BMWs!!?? Not sure what got into me . Fun BUT archaic.

I pulled together this picture of the wiring at the + battery terminal from a photo I took when disassembling the bavaria. I drew lines and arrows on it that identify the connections at the positive battery terminal.

Again...thanks all!!

Regards,
Bill

 

[Ohmess]

Bill -- I have some experience with electrical before I bought my coupe, and have done a lot of work on my coupe because of problems I found. Your labels are actually a good way to think about the connections to the battery.

1) The alternator to battery connection is used to charge the battery;
2) The battery to starter connection provides cranking power to start the car;
3) The "to other circuits" connection provides all of the unswitched power for the vehicle. A few of these connections are wired off of the battery to relays (headlights, horn, etc.), but most of these run through the fuse block; and
4) The "starter circuit" wiring you show is actually switched power, which runs through the ignition switch and then to the fuse block.

In general, switched power runs to the fuse block and is distributed on the back of the block across two fuse circuits. Unswitched power is also distributed like this. Here is a fuse block, I believe from a 1973 coupe (my 72 is somewhat different).

The large red wire connected here at the top of fuse 7 is unswitched power wired directly to the battery. The other spade connectors in the solid red area of this fuse block are also unswitched power, wired directly into whichever wire goes directly to the battery. In this picture, that black wire underneath the red wire is connected to unswitched power without a fuse. The area underneath the solid red area beneath fuse 7, here designated as red with white stripes, is unswitched power subject to fuse number 7. Note when troubleshooting, the wires subject to fuse 7 are connected. You can see on this block a connector with a single red/white stripe wire and a connector with three red/white stripe wires. Because these are both connected to lugs in the red with white stripe area, they are connected and form part of the circuit downstream from fuse 7.

Similarly, the area beneath fuse 6, designed as red with yellow stripes, is unswitched power subject to fuse number 6.

Switched power is also distributed before the fuses. The fat solid green wires at the top of fuses 4 and 5 are connected, as are the fat green wires on the spade lug beneath the fuse 5 wires. If you look closely, you will see a solid green background behind all three of these spade lugs. This connects these lugs electrically. The green with white stripes area underneath fuse 4 is switched power subject to fuse 4, and the green with black stripes area underneath the fuse 5 connections are fused switched power subject to fuse 5. In both cases, on this particular fuse block, there is only one switched, fused connection for each fuse.

 

[billpatterson]

Bill -- I have some experience with electrical before I bought my coupe, and have done a lot of work on my coupe because of problems I found. Your labels are actually a good way to think about the connections to the battery.

1) The alternator to battery connection is used to charge the battery;
2) The battery to starter connection provides cranking power to start the car;
3) The "to other circuits" connection provides all of the unswitched power for the vehicle. A few of these connections are wired off of the battery to relays (headlights, horn, etc.), but most of these run through the fuse block; and
4) The "starter circuit" wiring you show is actually switched power, which runs through the ignition switch and then to the fuse block.

In general, switched power runs to the fuse block and is distributed on the back of the block across two fuse circuits. Unswitched power is also distributed like this. Here is a fuse block, I believe from a 1973 coupe (my 72 is somewhat different).
View attachment 110166
The large red wire connected here at the top of fuse 7 is unswitched power wired directly to the battery. The other spade connectors in the solid red area of this fuse block are also unswitched power, wired directly into whichever wire goes directly to the battery. In this picture, that black wire underneath the red wire is connected to unswitched power without a fuse. The area underneath the solid red area beneath fuse 7, here designated as red with white stripes, is unswitched power subject to fuse number 7. Note when troubleshooting, the wires subject to fuse 7 are connected. You can see on this block a connector with a single red/white stripe wire and a connector with three red/white stripe wires. Because these are both connected to lugs in the red with white stripe area, they are connected and form part of the circuit downstream from fuse 7.

Similarly, the area beneath fuse 6, designed as red with yellow stripes, is unswitched power subject to fuse number 6.

Switched power is also distributed before the fuses. The fat solid green wires at the top of fuses 4 and 5 are connected, as are the fat green wires on the spade lug beneath the fuse 5 wires. If you look closely, you will see a solid green background behind all three of these spade lugs. This connects these lugs electrically. The green with white stripes area underneath fuse 4 is switched power subject to fuse 4, and the green with black stripes area underneath the fuse 5 connections are fused switched power subject to fuse 5. In both cases, on this particular fuse block, there is only one switched, fused connection for each fuse.

Hi Chris
Thank you! This post is coming in very handy as I wire up an electric fuel pump and the fuel pump controller for the B35 swap by https://www.revolutionelectronics.com/Products/Fuel_Pump.html

Regards
Bill