Rear battery relocation-dist block location? engine ground?

[Pablo M]

Ive got most/all the parts to relocate my battery to the trunk. I have a TEC brace/battery holder and all the e30 oem battery cables and such.

Where have people located the distribution block? On the firewall or in the cavity between the firewall and interior? I don't know the name, but passenger side of area where wiper motor lives. Photos would be helpful.

 

In doing this, do I need to ground the engine to the chassis, per this diagram? Is the current setup in my 72 2002tii have a separate engine ground already or am I adding one, and if so, where do I attach to engine?

 

Any advice appreciated.

I searched and did not find what I needed, but this image did come up a lot.

 

 

[SydneyTii]

Here you go, plenty to think about.

 

 

 

[Stevenc22]

Ground the battery in the trunk to the sheet metal

 

Then mount this in the engine bay and drill a hole through the fender. This will pickup the ground from sheet metal and give you a convenient stud to mount the engine ground and other battery grounds in the engine bay

 

 

 

Sorry! Something went wrong!

AMZN.TO

 

 

 

[jimk]

Stay out of of the ventilation system intake because it is exposed to the outside elements.  Mine is on the engine firewall approximately where it was on the E30.  Routed the cable on the passenger's side and up the firewall and is mostly concealed by the carpet.

 

I cut a hole to the right of the glovebox using a template I made to use the E30 firewall grommet and routed the cable into the void in the upper fender structure and out the oval hole to the junction block.  The short cable from the junction block to the starter runs approximately the same route as the E30, behind the engine to the starter.

 

The small wire in the E30 cable is installed to the junction block but not used at the moment.  It was power to the ECU as it was on the E30 but with the new VCU it is not needed.  (That wire has a fusable link a foot or so from the battery terminal, if shorted will burn out.  Replace with an in line circuit breaker if the link gets burned out)

Edited October 4, 2023 by jimk

[Dudeland]

I see that my article was quoted.  A brief update is that I am in the process of running the cables etc.  I just finished running the fuel lines (thank goodness that is done.  It was miserable). 

 

Design notes so far

1) I am running the master positive cable for the starter through the driver's side to a cutoff switch.  

2) I am running the output from the alternator to the cut-off switch. 

3) I am running 0 gauge cables. 

4) I have a mega fuse to install next to the battery (currently 250A)

5) I will be routing the cables (positive and negative) to the front to make sure that I have a good central ground point for my sensors and MS3 gold box

6) I have purchased the cutoff that has the wire wound resistor and terminals at the back to accommodate the correct switching procedures on shutdown.

7) Still researching if the wire wound resistor is required if the alternator is connected directly to the battery via the post on the cutoff switch.  From what I can read the wire-wound resistor is required in case of flyback voltage when you shut off the car via the cutoff switch, as the alternator will be connected to the battery, it should absorb any flyback voltage.. but still reading

😎 Going with an optima battery with proper hold down in the trunk.   I think Yellow is going to be the call. 

9) Routing the cables down the passenger side transmission tunnel to keep them away from potential shorts from side impact.   

10) Using weld-on zip tie tabs with rubber hose protection to ensure that there is no rub through the already thick insulation on the 0 gauge wire. 

11) Yes I understand I am adding about 5-6 lbs to the car using heavy gauge cable, but chasing issues with an ECU as a result of bad grounds is a greater issue.  

12) I will run a positive from the starter to the battery area to accommodate the chassis power requirements. 

13) I will be installing an enclosed aftermarket fusebox under the back seat to clean up the relays installed there. 

14) I will be installing a chassis ground to the battery area and to the engine from a central ground point under the dash.  This will be used for chassis ground, as well as ECU and engine ground. (i.e. star configuration ground system) 

15) All large connectors are crimped with the use of a small amount of conductive grease (no... not dielectric grease). (Boy now I have done it!).

 

Regards

 

 

[2002iii]

I put the e30 junction base behind the brake booster right above the brake light switch. This way the factory positive cable from the starter will reach it.

 

I ran the cable up the drivers side inside, it fit nicely in the factory wiring channel. I used a factory hole I found in the firewall above the clutch pedal.

[Pablo M]

6 hours ago, 2002iii said:

I put the e30 junction base behind the brake booster right above the brake light switch. This way the factory positive cable from the starter will reach it.

 

I ran the cable up the drivers side inside, it fit nicely in the factory wiring channel. I used a factory hole I found in the firewall above the clutch pedal.

I was wondering if there was any built in way to hood the cable in place along the bottom edge of the passenger side. Sounds like the drivers side is the way to go. Thanks. 

[jimk]

2 hours ago, Pablo M said:

I was wondering if there was any built in way to hood the cable in place along the bottom edge of the passenger side. Sounds like the drivers side is the way to go. Thanks. 

Ran it in the same routing my old fuel line was except leaving the trunk, the cable went over the wheel well through the hole that is stuffed with foam rubber.

Edited October 5, 2023 by jimk

[Dudeland]

On 10/4/2023 at 9:18 AM, jimk said:

Stay out of of the ventilation system intake because it is exposed to the outside elements.  Mine is on the engine firewall approximately where it was on the E30.  Routed the cable on the passenger's side and up the firewall and is mostly concealed by the carpet.

 

I cut a hole to the right of the glovebox using a template I made to use the E30 firewall grommet and routed the cable into the void in the upper fender structure and out the oval hole to the junction block.  The short cable from the junction block to the starter runs approximately the same route as the E30, behind the engine to the starter.

 

The small wire in the E30 cable is installed to the junction block but not used at the moment.  It was power to the ECU as it was on the E30 but with the new VCU it is not needed.  (That wire has a fusable link a foot or so from the battery terminal, if shorted will burn out.  Replace with an in line circuit breaker if the link gets burned out)

How is that Halltech treating you?  Still going strong?

[jimk]

55 minutes ago, Dudeland said:

How is that Halltech treating you?  Still going strong?

Upgraded to an R3 so no more wires thru the firewall, no more tuning USB cable (wireless), no more remote relays (all in the box), fan controller in the box, wideband controller in the box.  I have a 1500 and a 2500 available on the shelf.

Edited October 5, 2023 by jimk

[Dudeland]

Ignore

 

 

Edited October 6, 2023 by Dudeland
Repeat

[TobyB]

As to the ground- 

find something a bit better than sheet metal to bolt to,

OR use a nice big copper washer.

Reason being, steel has a fair bit of resistance to it, and when you 

look at how little contact area a single bolt and lock washer has, 

you're creating quite a bit of electrical resistance right at that junction.

Add a little corrosion, and you're down to less than a square mm.

 

But:

Spread it out a bit, and you're good to go.  

OEM BMW seems to be at least a square centimeter lug

welded to the panel for any sheet metal ground

that takes significant current...

 

t

 

[Son of Marty]

Like Toby said large copper washers are the bomb, I use the trunk bulkhead behind the rear seat drill through and clean a spot down to bare metal as large as your washers on each side then sandwich on each side of bulkhead bolt down firmly then paint over the washers then you can bolt your grounds to that using a 2nd nut remember it will need to carry 150 amps or more on a cold start. 

Edited October 5, 2023 by Son of Marty

[Lucky 7]

I mounted the junction block to the firewall and mounted a busbar next door for all my hot leads. 
 

 

I routed battery ground to a rear seatbelt mounting point since I was initially planning on a seat delete. My plan now is leaning toward a partially deleted back seat, so I may add belts back in. In that case, I’ll take Son of Marty’s suggestion above and just go to sheet metal. 
 

I ran a flexible ground strap from the oil pan to the frame extension behind the drivers headlight. You can see it here between the alternator and headlight. Strip paint, dielectric grease, bolt it down tight. 
 

 

So far so good. I’ve chased a lot of electrical gremlins, but none of them were because of bad grounds or the battery relocation. It’s been running reliably for awhile now, which is nice. 

[Dudeland]

I just finished welding on some tabs on the underside of the floor to tie my fuel lines to.  It was surprising how hard it was to get a ground clamp to work on the car.  I tried the right rear brace in the trunk as well as the right rear tower and still, I found that I was getting some booger welds as a result of a poor welding ground.  

 

I thought it was BS that you needed to have a central ground for the ECU and sensors, but welding the floor made me a believer. It is hard to think that all that metal with all those joints and still it will act like a big resistor. 

 

Regards