MSP battery relocation project

dmention7

Member
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'03.5 Blue MSP #2543
A little background: in order to fit the IC core for the water-air IC setup I'm planning, I decided to relocate the battery to the trunk. After a little bit of planning and putzing around, I finished the project up last night. Here's a material list and a basic walkthrough...

Parts/Materials
-25' of 0 gauge welding cable (I got mine here)
-Group 24 marine battery box (about $12 at an auto parts store)
-150 amp circuit breaker (I used this one)
-Distribution block, preferably with both fused and unfused outputs (This is what I used)
-0 gauge ring terminals with both 5/16" and 3/8" holes.
-Battery terminals with ring terminal connections (Like this)
-zip-ties
-electrical solder

Tools Needed
-Various metric sockets (specifically 10,11,12,14,17mm)
-Drill/bits
-Propane torch
-Large linesman pliars (or something specifically for cutting heavy cable)
-Bench-mounted vice
-Utility knife


First thing I did was pull up the carpet in the trunk look for a suitable pass-through for the main battery cable. I decided after nosing around the car for 30 minutes or so, that routing the cable under the car would be less hassle than going under the carpet and drilling a hole in the firewall. Right at the back of the spare tire area, there's a giant rubber grommet--perfect! I drilled a 1/2" hole through that, then pulled about 4 feet of the 0 gauge up through from the bottom; enough to locate the battery anywhere in the trunk.

From the top, and from the bottom


I decided to run the cable up along the drivers' side of the car. I went up over the rear crossmember, above the lip of the gas tank, and then along the brake lines, securing with zip-ties as often as necessary to ensure the cable doesn't sag. There are probably better ways to secure the cable, but didn't feel like drilling holes into the floorpan if I didn't have to.

Pics, going from the rear of the car to the front


Finally, I pulled the cable up along the firewall, making sure it was going to be clear of the axles and suspension. Sorry, no good pics except for where the cable ended up in the engine bay


Now that the power cable was in place, I decided to locate the ground wire. If you pull away the trim in the trunk, the bracket that holds the seats to the frame offers a nice heavy secure bolt to ground to. I used a wire brush to clean up the metal around the bolt and on the bracket itself. A ring terminal with a 3/8" hole was perfect.


I guess this would be a good place to point out why I listed solder and a propane torch in the tools/materials. Main reason is that securely crimping those large terminals is a PITA without the proper tool (which I don't have). An alternate method I read about requires that the wire attachment point be closed at the end, like this as opposed to open like this. Once you've stripped the end of the wire, you put the ring terminal in a vise with the wire opening pointing straight up, and fill the wire opening with bits of solder (like literally fill it). Then you torch the terminal until all the solder melts and jam the end of the wire in there. If done properly, it makes a damn good mechanical and electrical connection. Anyways, back to the walkthrough....

I then went back to the engine bay, removed the strut bar, unhooked the battery, removed it, and removed the battery tray


The distribution block I bought has three fused outputs and one unfused output. Given that the stock battery connection has a cable running to the fuse box, and a larger cable that I assume runs back to the starter/alternator, I ultimately decided it was fine (and simpler) to hook both of those to the unfused output. For lack of a good idea on where to permanently mount the distro block, I just zip-tied it to the fusebox lid.


Now back to the trunk to mount the circuit breaker and locate the battery box. I decided mounting the circuit breaker to the battery box was as good of an idea as any. I just drilled a couple 3/8" holes and used some spare machine screws to mount it.


The circuit breaker has 5/16" studs, so that's where the ring terminals with smaller holes come in handy. The main power cable gets attached to one of the terminals on the breaker, and then I cut a short piece of cable to run from the battery terminal to the breaker. Note the battery terminals I linked to use a 3/8" ring terminal


All I had left now was to mount the battery box. The one I bought just uses a couple of brackets that screw into the frame, and then a strap that holds the box to the brackets. Not an ideal solution, but it holds everything down tightly. I was deciding between two locations. Behind the passenger sidewheelwell, or up against the rear passenger side seat. Against the passenger seat probably gives a better weight distribution, but it would completely block off any storage with the seat folded down. So I put it in the nook behind the wheel well.


As a final test, I hooked up the negative terminal and turned the key. She fired right up! I was a little concerned that a 150 amp breaker wouldn't handle the current from the starter, but I saw a walkthrough on a subie, where only a 100 amp breaker was used, so I should be okay. The real test will be on a cold morning in the winter when the starter sees it's maximum load.

Here's my filthy dirty engine bay, sans battery! Oh, and a box the approximate size and location of the l-a IC core I'll be ordering soon



I've got a couple things I want to clean up, but they are lower priority now that everything is functional. Main thing is that I want to replace the main power and ground cables in the engine bay with something a bit beefier. I haven't taken the time to trace them down yet, but does anyone know off-hand where the power and ground cables from the factory battery terminals run? Straight to the alternator? I also think I want to eventually replace the battery box with something that uses a standard tie-down.
 
you dont need that dist. block.. you should have just ran the 0 gauge to the main 100 amp fuse in the fuse box, and also hooked the alternator charge wire there also... also get a 100 amp fuse or breaker for the battery side considering thats whats in the fuse box.. you want the same or less
 
I know I don't *need* the distro block, I just got it because I wasn't 100% sure how I wanted to hook everything up, so I wanted to maximize my options. But since I am planning to go in there and clean things up a bit at some point, I'll keep your suggestion in mind.

So just for clarification, of the two power wires that normally came off the battery, one goes to the fuse box... and the other goes straight to the alternator? I was thinking for some reason that also heads down to the starter motor.
 
i havnt really looked at it but i believe its the alternator wire... but ya just run the ring terminals right to the fuse side.. i would change that 150 for a 100 tho, because with it higher than the other its really not doing anything
 
Nice install, is there a kit available for the MSP? I relocated the battery to the trunk in my old 94 Cobra and it made a noticeable difference in handling.
 
No kits that I'm aware of, but it was a pretty easy job with a little bit of improvisation on hand ;)

I suppose the circuit breaker isn't strictly required, but with all that wire running between the battery and the nearest fuse, it's nice to know that a cut to the wire insulation won't result in the battery discharging itself to the frame of the car. Plus, it's a nice quick battery cutoff when you're working on the car. Though I have heard that it's not good to cycle them too much because they can lose their ability to trip at the stated amperage.
 
i dont know if thats entirely true - their trip capacity is due to thermal expansion differences between two metals. id say youd have to cycle it a few hundred times before that would even be on the radar as a potential problem.
 
Pretty much a carbon copy of what I did - but with the battery on the driver's side in the boot and the 0 gauge wire running down the drivers footstep.

I want to add a power distribution block too. I want to have one side with constant power and the other switched on accessories. It will involve a bit of soldering but I think it won't be too hard.
 

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