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Battery Relocation Question, Small Wire


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I have a question regarding the relocation of my battery to the truck. I am using an e30 cable with mounting block. In the engine compartment I know I have to attach the main cable to the starter and ground the block to the body. What is confusing me is the small cable. The current (factory) positive cable goes to the starter with a small cable running into a wire harness, which I do not want to unwrap. On the e30 cable where do I attach the small cable from the battery? Does it go to the fuse block, if so where, if not what do I do with it? I have a 75. I have read the FAQ, looked a my wiring diagram and searched, but I cannot find the answer I am looking for or am looking right past it. Thanks

1975; 2002

1995; 318ti

2004; 330i ZHP

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stock battery terminal on your '02, it must be attached to the engine compartment end of the new E30 cable. It powers things (and I don't remember exactly what) that are live even when the ignition is off. You should be able to attach the wire's ring terminal to the E30 cable; if it's too small, buy a larger terminal and solder it to the wire.

Don't leave it off, though; it's important.


'69 Nevada sunroof-Wolfgang-bought new
'73 Sahara sunroof-Ludwig-since '78
'91 Brillantrot 318is sunroof-Georg Friederich 
Fiat Topolini (Benito & Luigi), Renault 4CVs (Anatole, Lucky Pierre, Brigette) & Kermit, the Bugeye Sprite

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there to provide a separate power source for the various "keep-alive" circuits in the car (stereo, clock, on-board computer, Motronic memory, etc) if the main cable needs to be disconnected at the firewall junction block (if, for example the starter needs to be removed) but there's no need to remove the battery.

It's more or less optional whether to use it in a trunk mount battery relocation on an '02 - when I did the relocation on my '71, I put a battery disconnect switch in the main cable as an anti-theft device (pretty hard to steal the car if no battery power will go to the starter or ignition), kept the small cable (with a 30 amp circuit breaker spliced in) and used it to power the interior lights and the keep-alive circuit in the stereo.

Barry Allen
'69 Sunroof - sold
'82 E21 (daily driver), '82 633CSi (wife's driver) - both sold
66 Chevy Nova wagon (yard & parts hauler)

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  • 6 years later...

Bumping this old thread because i am starting my battery relocation to the back seat.. I bought an E30 cable off of a forum member but it has this plastic piece spliced into the small wire. Is this normal? I tried looking for pictures of other E30 cables but didn't see anything similar.

I was thinking that i would wrap it in electrical tape, then put some heat shrink over it.

It also has this split in the main cable. Was going to tape and heat shrink that as well.

Sound like a plan?



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Also, does anyone know the size of the stock engine ground wire on a 72 non-tii? I've searched but no luck.

I'm looking at this one from Summit. It's 10 GA stainlees steel 11 inches long.


I'm using this on now.  Haven't burned it up yet!  It's plenty heavy.  Although I seem to have one heavier than 10gauge.

Edited by jimk

A radiator shop is a good place to take a leak.


I have no idea what I'm doing but I know I'm really good at it.

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I'm using this on now.  Haven't burned it up yet!  It's plenty heavy.  Although I seem to have one heavier than 10gauge.

Thanks Jim. I picked up one from Autozone today, but it's really thin. Think I might grab a heavier gauge on from Summit.

On a side note, the relocation was going pretty well until it came time to take the cable to the engine bay. I have zero room to drill through my firewall, so I am routing the cable next to the trunk latch and into the engine bay using the existing opening by the fuse box. What a pain in the arse! There is hardly any room to navigate in there and my hands are trashed lol.

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