Most cars are nose-heavy, and so relocating that big, heavy block of lead and sulfuric acid to the rear will help the handling and— if it’s rear-wheel-drive— launching at the drag strip. You can buy ready-made battery-relocation kits, or you can buy some shiny new welding cable and put terminals on it… or you can do it junkyard style. Thanks to much experience learned in the 24 Hours of LeMons race series, we’ve got some useful tips for the junkyard shopper hoping to score a nice long battery cable that will reach from the starter motor all the way to the positive terminal of the battery in your trunk.
Plenty of high-end, high-performance cars came with trunk-mounted batteries from the factory, but you won’t find many such machines in your local self-service U-Wrench-It yard, the kind where all battery cables are the same low price, regardless of length. These days, most of the trunk-battery-equipped cars you’ll find in this kind of yard are going to be European cars of the 1990s and 2000s. The Jaguar S-Type (and its Lincoln LS sibling), big Audis and Benzes, Volvo S60s and S80s, and so forth— plenty to choose from when you’re looking at cars that had fall-off-a-cliff depreciation after they hit about age ten. However, the BMW E30 and E36 3-Series cars offer the best combination of fat cable, quality materials and components, and ease of removal.
The E30 is getting a little bit hard to find in junkyards nowadays, and not every example came with a trunk-mounted battery. If you spot an E30 (the boxy 3-Series built throughout most of the 1980s) and it’s a 325i or 325iS, it probably came from the factory with a battery in the trunk.
The E30’s 1990s successor, the E36, is now laughably easy to find in a big self-service wrecking yard, and every one I have seen has a trunk-mount battery. The first thing you do when you find an E36 on a cable hunt is take a look in the trunk. If the cable terminals are gone (many lazy junkyard employees slice off the terminals when harvesting batteries), move on to the next car— one of the main reasons to get a BMW cable is the excellent quality of the permanently-affixed battery terminals.
When you see this in the trunk, you’ve found your battery-cable donor car. I’m not sure what wire gauge these cables are, but they’re thick, maybe 0-gauge or better. Note the smaller accessory cable fused into the terminal; this gives you more options when wiring a race car.
To remove the cable, you’ll need to pop out the back seat and remove the bolts that hold in the front passenger seat. One of the reasons it’s much easier to remove the battery cable from the 3-Series versus, say, a Volvo S80, is that it’s much more difficult to get to the fasteners in a power seat (unless you bring a 12-volt battery pack to the junkyard). Yes, this is a photograph of a Subaru Outback seat, but the principle is the same.
Once you have the seats out, yank the carpeting out of the way, then pry off any plastic shields over the battery cable. You’ll need to take a knife and slice the grommets that seal the openings through which the cable passes into the trunk and engine compartment. Cut the cable as far into the engine compartment as you’re willing to go, then go around to the trunk and pull it all the way out. Most self-service yards with standardized pricing charge between $5 and $10 for a battery cable, even one that happens to be 15 feet long and twice as thick as an ordinary cable.
Here’s a BMW cable on a rear-mounted battery I put in a 1967 Austin-Healey Sprite a few years back. Naturally, a BMW E36 cable is going into my 1941 Plymouth road racer project, too.