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Discussion Starter #1
I’m considering relocating my battery to the trunk to make room for a cold air kit. I’m also going to put a master disconnect in the trunk. I see some disconnects have an alternator option and some don’t. If I buy one without the alternator terminal, can I not just run my alternator battery wire alongside the positive cable in order for the alternator to charge my battery? I assume the ones without an alternator terminal are typically used on racecars and they’re not concerned with charging the battery. Thanks, Matt
 

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You can do this a few ways with putting the battery in the trunk along with a master disconnect switch in the trunk.

Most master disconnect switches have two posts to where when the switch is closed, the one post is connected to the other.

The other style with 4 post master disconnects are basically two 2 terminal switches in one housing with one knob that either makes connections or breaks connections.

If you wanted to stop the flow of power off of the battery from going to the alternator, starter, and other electronics in the car, you would take a standard 2 post switch and connect one post to the positive post of the battery and then the other post to everything else requiring power. Now if the car is sitting there and the switch is open, then no power is passing past the switch since it is in the OFF position.

An issue can arise with turning the switch ON and then starting the car and then turning the switch to the OFF position and still have the motor running. This is due to the alternator feeding the ignition system and this keeps the motor running.

This is the reason for a using a 4 post disconnect switch. Now when the car is running and the switch turned off, the output from the alternator is now also disconnected to where it cannot feed the ignition system to allow the motor to continue to run.

Now, depending on the alternator and wiring, sometimes adding a basic diode on a particular wire on the alternator, if the two post switch is turned off, then the alternator is kept from feeding the ignition system and thus the motor should stop.

You are asking about simply relocating the battery to the trunk but we may need to ask, are you thinking about using and installing a Ford style starter solenoid in the car for the starter ?. If you are and this solenoid is in the trunk, then the wiring will get a tad more involved. Basically if you have a battery up front and just want to move it to the rear, all you have to do is extend the positive cable back to the rear as well as the ground and then put in a basic two post disconnect switch anywhere along this length of new cable from the front to the back.

When thinking about relocating the battery in the rear, keep in mind that your cabling size also needs to be increased. We are dealing with a low voltage of 12 volts and loosing a few volts due to undersized or poorly terminated wire can be a problem unlike home wiring that starts at 120 volts and a few volts lost there is not as much of an issue.

When shopping for a disconnect switch, keep in mind the amp rating on them. Cheap switches will not pass the amperage like a better one and since all of the power will be passing though this switch, if it slowly degrades over time you may be out in the middle of nowhere if a cheap one does fail.

You might also do some searches on this site as well as others.

Personally I would add the proper size fuse at the battery positive post so that if a short does occur, a simple fuse will blow and not create near the issues from running without one in that what a burning wire could do to things.

Here is how a lot of GM cars are wired with the battery under the hood:



Here is a diagram with simply relocating the battery to the rear:



Here is a drawing of a battery in the rear with proper protection on the wiring:



Jim
 

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Discussion Starter #4 (Edited)
Great info guys! I appreciate it a lot. Isn’t that junction block or similar already mounted on most 3rd Gen’s already up on the core support on the front side by the battery? I like the of not having the positive wire to the starter “hot” at all times. So maybe a combination of a disconnect and solenoid would work? My main confusion is why Jeg’s offers a Moroso brand disconnect w/alternator and one wo/alternator. I assumed that it depends on rather you even had an alternator as I know most race cars don’t. Since I do and would like to keep my battery charged I would simply buy the one with an alternator terminal and run the 14 ga wire currently running from the battery to the alternator, through the disconnect first and then back to the alternator. If not, the battery would get no charge, correct? Or I would hook it on the same terminal as the starter wire at the disconnect and not use the one stated for cars with alternators.
ETA: I’m also considering using welding lead for the cables. Any thoughts on that?
 

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Discussion Starter #5
I just looked over my car again to see exactly how it is wired currently. The smaller red (12 ga?) wire coming off the battery goes on to a junction block mounted right next to the battery. From the second post on the junction block it the wire then run underneath the top of the core support and appears to connect to the buss bar on the horn relay. The other terminal on the horn relay has a fusible link coming off it and disappears back into the same wiring harness that the junction block wire is in. Not real sure where it goes from there, but there is another what appears to be red wire coming of the voltage regulator that disappears into the same harness. Back over by the junction block there is a group of three wires that run to the alternator. I am assuming, and please correct me if I’m wrong as I’m not a wiring expert, that the fusible link coming off the horn relay buss bar then continues on I suppose to the fuse block. So, not exactly as your drawing simulates it is similar. It all appears to be factory wiring, but I can’t gaurantee that. With that being said, is the best set up still gonna be the third drawing depicted in Jim’s post?

Also I had read on this site somewhere that the big wire going to the starter is not fused because the amperage going through the wire needs to have full battery power going to the starter and due to the potential high amperage possibility while starting could possibly trip the fuse. Maybe an ANL fuse takes care of that problem as I’m not aware what that type fuse is.

I’m still not sure what is the best way to wire my battery if I move it to the trunk. I do want to at least use a disconnect. The solenoid would be an option I’d like to use as well. I’ve looked at the M.A.D. site and their products and diagrams they show on there. Anymore help to make me understand exactly what I need to buy and how to wire it would be greatly appreciated. Thanks, Matt.
 

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Discussion Starter #6
Oh, one more thing. If I use the solenoid do I move the ignition wire currently going to the starter solenoid or do I piggyback another wire onto that terminal to go to the new solenoid for a signal. What a pain in the butt! All I want to do is get the battery out of the way in order to utilize that space for a cold air induction tube.
 

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What a pain in the butt! All I want to do is get the battery out of the way in order to utilize that space for a cold air induction tube.
OEM's like BMW and Volvo simply use a 16' battery cable and put the battery in a well in the trunk. No switches, solenoids, extra wires, just a longer battery cable that runs right through the cabin.
 

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Discussion Starter #8
I always like your answers Mike. Always straight to the point. I don’t have problem doing that at all. My main reason for asking the question originally was to find out why Jeg’s sells two different disconnects, one with an alternator terminal and one with. I just wanted to know the difference in the two. And I want to be able to charge the battery as I drive. I want thd disconnect for my preference only and if I go to thd track I believe they require one. Just logically thinking I believe I can just lift the battery out of the tray and set it in the trunk in its new battery hold down. Of course, I’ll need to run a longer starter cable. I will also have to run a longer wire from thd positive post of the battery to tie into the wire going to thd factory junction block mounted next to the battery in its original location. The question I was really seeking is the difference in a disconnector with a separate alternator terminal and what it would be used for. Obviously I could just lengthen that wire to reach the trunk and put a terminal on it and hook it to the positive battery post. Not the most professional way to do it, but I’m sure it would work. My main concern is why they offer a different disconnector with a different terminal for an alternator.
 

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Obviously I could just lengthen that wire to reach the trunk and put a terminal on it and hook it to the positive battery post. Not the most professional way to do it, but I’m sure it would work.
That's how the professional engineers at BMW, Volvo, Saturn and other OEM's did it. They are all run through the cabin, well secured and with no chafing points. The ground connections are to a bolt on the rear frame.
 

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You can do a "very" basic battery relocation by removing the existing battery and putting it in the trunk and then up front you then remove the existing positive battery cable that was off of the battery when in front down to the starter and leave it off of the car.

Now there is a wire that was a fusible link between the up front battery post and the junction block on the backside of the radiator support. This wire depending on how it was attached to the original battery positive post when the battery was up front is you need to take this section of fusible link off of the junction block and attach one end of it to the starter's battery cable post and then since it will not be long enough, extend the other end with at LEAST a 10 gauge wire to reach to the junction block on the backside of the radiator support.

Now you need to look at things and figure out your best plan of attack but your battery negative post when up front had a large cable off of it to the engine block or the alternator bracket or somewhere on the motor. This cable now need to be either reused and connected to another point or removed and not be on the vehicle. This cable may also have had a smaller wire off of it which should be a fusible link and the end of this smaller wire attached to either a bolt on the backside of the radiator support or a lip on the passenger fender.

Staying on point with this ground cable, you could then terminate the end of this big ground cable to a nut and bolt connection on the firewall while still leaving the other end attached where it was on the block, alternator bracket, or where ever. By making this connection you have now ties the engine, starter, alternator and engine sensors grounds to the body of the car.

Now looking at the car, you have a connection to get power from the starters positive post connection to the rest of the car like it was before and still protected like it was with the fusible link.

You now also have the engine, starter, alternator, engine sensors, and everything else grounded to the car body tied together.

What we lack now is connections to the battery.

This is where I can get into conflict with others but still be supported by anyone else that knows what happens when a wire or cable is unprotected and a short does occur.

Stay with me here but now you ahve your battery in the trunk with a positive post and a negative post that needs to be connected.

Lets start on the negative battery post. You now need to make up a cable to go from the negative battery post to a spot in the rear of the car and this cable needs to be at least the size of what was originally under the hood when the battery was up front. This connection to the car's metal in the back must be solid AND electrically sound and the cable when terminated should be nut and bolted to the metal and not be attached with metal self tap screws AND all paint and whatever must be removed so electrically this power flows easily. Hopefully on the front ground connection you have also done the same with a solid electrical connection and not had the cables terminal sitting on top of paint and junk.

Now we are getting close to being done. Here is where you need to get a new cable long enough to reach between the battery positive post and the starters battery stud and this cable needs to be large enough to limit voltage drops so that the motor still cranks over like it did before when the battery was up front.

Since we do not know what starter you have and what cranking pressures you are trying to over come with the engines pistons and cam timing, is lean towards bigger cabling.

Once you get the proper size cable and properly terminate it and connect it into the car, the car should fire up and run as it did before.

The rub here in my book doing it like above is there is NO protection on this big cable. Granted a LOT of vehicle companies do not do it now, more and more ARE doing things to protect this cable should an accident occur. Also more and more standards are being upgraded in the boating industry which also share a lot of 12V circuits we have in an automobile. Drag racing standard are also being upgrade to include vehicles that are electrically powered and not with combustion engines.

If you have ever experienced a short on a wire or cable and seen it melt it's insulation off you will start wondering, is there a way to prevent this and there is. Look at your house. What happens when a short occurs on a wire or cable or a light switch shorts out ?. A breaker or fuse opens up to stop the flow of electricity unless it's been put in the wrong way. Just like on your car already, you have fusible links to protect wiring as well as fuses in the fuse block to protect wiring. What happens if you take these things out and a short were to occur ?. PLENTY.

While I would love to say that I can route a battery cable from the battery all the way up front and have it protected from things I KNOW could cause issues like the wire going across a sharp metal edge or have it placed away from excessive heat and properly secured BUT I have NO idea what can happen in an accident. This cable could then become pinched and shorted to ground and without the proper parts your 1000 cranking amp battery will be dumping this current into the short and a small 4 gauge, 2 gauge, 1/0 wire and so on not designed for this amount of current will break down and more damage will occur than just at the point of the short.

I'll get on my chair or high horse here to say, a master on off switch requires someone to turn it on AND off. Fuses, circuit breakers and fusible links are designed open circuits and stop the flow of power ALL BY THEMSELVES. If you get in a bad enough accident, what happens if you cannot get to the master on/off switch to cut power ?. What happens if you are at a track following the rules with the relocated battery and a master on/off switch and have an accident and it takes a while before the track safety person gets there ?. What happens at a track and the car is so badly damaged that they cannot even find the switch to turn it off ?. With the proper wire protection such as fuses. circuit breakers and fusible links AT the source of power the electrical system is more properly protected.

Here is a VERY basic wiring diagram and the variable is how you might do the ground connections:



Here is also some pictures of a newer vehicle (Jaguar) with a trunk mounted battery and fusing on that cable that runs all the way up front to the engine starter and the rest of the electrical system:



Here is a car from Drag week that the cable shorted out and the interior filled with smoke while on a drive between tracks:



And an unprotected cable on a commercial rig:



Do what you want but I don't want to have this happen to any of my vehicles with a battery in the trunk.

Oh, and a mustang that he forgot to run a wire thought a grommet:



And another drawing I had from a while back:



Food for thought but don't forget to solidly mount the battery where ever it will be and properly vent it.

And I know you asked this before but on the master switches:

As far as the different disconnect's Jeg's offers (and I don't know which ones you have been looking at) is they do different things AND have different ratings on them. For example, they offer a disconnect model 74100 and it is for w/o alternator and is a two post disconnect switch. The ratings or specifications on it are 20A continuous and 125A surge. The 74102 is for with an alternator and it is a 4 post disconnect switch and the ratings or specifications for it are 300A continuous and 2000A surge. Just find out what you need there and what they offer and go with a higher than needed spec for added cushion or for supporting some future upgrades.


Jim
 

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Jim, do you have any more info on that Jaguar part?

I'm curious on the price and if I could order one.
 

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Discussion Starter #13 (Edited)
Looks like I have a lot to digest. I dont want it too complicated, but I want it somewhat safe. Is an ANL fuse similar to the mighty mite fuses you see nowadays? I was hoping to be able to move it to the trunk fairly cheap, but by the time you add up the fuse and junction block and various other pieces it adds up quick!
 

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If the price of fuseboxes seems steep, check out your local boneyard. There are many models of cars with batteries in the rear that have a fusebox located right at the battery. Pick-n-Pull sells them for about $20, and the associated long battery cable is about $6. Here's one from a BMW E39:

 

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If the price of fuseboxes seems steep, check out your local boneyard. There are many models of cars with batteries in the rear that have a fusebox located right at the battery. Pick-n-Pull sells them for about $20, and the associated long battery cable is about $6. Here's one from a BMW E39:

Very nice. A person could even get two of these for that price and you would have all the spare fuses on hand when on a road trip.
 

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Jim, do you have any more info on that Jaguar part?

I'm curious on the price and if I could order one.
The Jaguar picture was something I found on the internet but companies like Bussman like NCDEERE stated have different things that might fit your needs.

Another good option like Mike shows is using things from salvage yards.

And don't limit yourself to automotive parts as you might find something that works from the boating or aviation industry.

I found this style of battery fuse on some boating sites:



Single Stud Fuse:


Double Stud Fuse:


I also would design the connections and cables to where if the fuse were to blow, you could move the one cable off of the fused side of the fuse block over to the battery side once the issue of why the fuse blew to at least get you home. I would also carry a spare fuse as some of these large specialized fuses are not readily available in the middle of no where.

Jim
 

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Discussion Starter #17 (Edited)
How big a fuse do you think would be necessary for the standard automobile? I'm sure it varies depending on what exactly your trying to start. I know my son's newish Chevrolet has like a 175 amp mighty fuse next to the battery. Not sure if that's big enough or not. My motor is like a 10:1 383. Nothing exotic.

E.T.A. I believe it's a Mega fuse not mighty.
 

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Jim, do you have any more info on that Jaguar part?

I'm curious on the price and if I could order one.
The Jaguar picture was something I found on the internet but companies like Bussman like NCDEERE stated have different things that might fit your needs.

Another good option like Mike shows is using things from salvage yards.

And don't limit yourself to automotive parts as you might find something that works from the boating or aviation industry.

I found this style of battery fuse on some boating sites:



Single Stud Fuse:


Double Stud Fuse:


I also would design the connections and cables to where if the fuse were to blow, you could move the one cable off of the fused side of the fuse block over to the battery side once the issue of why the fuse blew to at least get you home. I would also carry a spare fuse as some of these large specialized fuses are not readily available in the middle of no where.

Jim
That is one of the cleanest options i've seen. What about an automotive breaker Im pretty sure I have seen someone on here use one.
 

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Battery Relocation?

My solution was to resize the battery and leave it on the core support. With the wiring and mounting expense to move the battery to the rear, a lithium battery was only slightly more than a good AGM battery. And I didn't have to deal with rewiring. When you throw in the fact that the lithium battery should last longer, cost is a wash.

Keith C.
 

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