Electrical – Replace Battery Cables and Relocate Battery

This guide covers how to replace the stock battery cables, as well as how to relocate the battery to the trunk.

Preparation

Understanding how the electrical system of a car works is ideal for this project.
Don’t worry it’s not that complicated and I’ll walk you through it.

Note: If you are already confident in how electrical systems work in cars, skip ahead to “The Plan”.

How Automotive Electrical Systems Work

Every car has a battery to store and provide electricity.

In order for any electrical component to run (lights, stereo, spark plugs, etc.) power needs to flow from the battery through the component and then back to the battery. It doesn’t really matter which way you visualize the power flowing, just as long as you stick with a consistent direction (i.e. positive to negative OR negative to positive).

That’s it. Pretty simple, right?

The Main Electrical Components of a Car

For simplification, there are four main electrical components of a car:

  • 12 Volt DC Battery
  • Starter
  • Spark Plugs
  • Alternator

In order for a car to start, the starter motor must crank start the engine. Doing this uses up some of the stored charge in the battery.

With the car running, spark plugs (and the rest of the ignition system) continue to use up more of the stored charge in the battery. Any other electrical accessories will also drain the battery too.

To prevent the car from using up all of the stored charge in the battery and dying, the alternator charges up the battery using the mechanical power of the engine itself.

Complete Electrical Circuits

So at this point you may be wondering:
“How does the power flow through the starter or spark plugs back to the battery?”

That’s simple, the metal body of the car itself — known as the “ground connection“.

While you could technically run both positive and negative wires to and from each component you want to power with the battery, doing so uses a lot of wire and would be pretty messy. To keep things tidy, auto makers made it so that nearly all components connect to the body in some way, and then one big fat wire connects the body back to the battery.

Now that we know the basics, let’s discuss the plan for how the actual components will be connected in the AW11.

The Plan

Rough Sketch and Details

Here’s a rough diagram I made to show the existing lines and how they will be replaced by new lines:

M2 Connector = The gray connector in the engine bay with 4 pins.
N1 Connector = The “Molex” connector in the trunk that connects to the engine harness.
Body (-) Ground = The part of the starter/alternator that connects to the engine.

The positive side of the battery must connect to the big terminal on the starter motor directly. This is because of the high amount of amps that gets drawn through the wire.

The positive side of the battery must also have another line going to the big terminal on the alternator. Rather than using a direct connection, a 100 Amp fuse is placed along the line. Using a fuse on this line ensures that you don’t start a fire and/or destroy electrical components if too much current goes through the wire.

On that same positive wire (after the fuse), one line connects to the solid white wire of the 3-wire connector on the alternator (the top one), and another two lines connect to the solid white and solid black lines of the M2 connector (the gray one with 4 wires in the engine bay by the left strut tower).

Note: The stock “fuse” is actually a thinner piece of wire called a “fusible link”. It essentially just melts before any electrical damage can be done, breaking the circuit.

The negative side of the battery will have two seperate lines, one to ground to the body and the other to ground to the transmission — in order for a complete electric circuit to be made by all components.

The small terminal on the starter will connect to the black wire with a white stripe on the M2 connector.

Mockup Diagram

Here’s a mockup of all the new lines going into the engine bay:

Note: While not shown in the diagram above, my battery is being relocated into the trunk. To do this I am using the pass through holes between the trunk and the engine bay to run the wires.

Connectors and Wires

Here’s a few images showing how the wires connect to the starter, the M2 connector, and the alternator plug:

Parts List

NoteO’Reilly’s is a great place for cheap but quality cables. They are sold by the foot and are actually made of copper, instead of CCA (copper clad aluminum).

Steps

1. Put the car up on jack stands (we will need to access the starter and the bottom of the alternator later on).

2. Disconnect the battery — start with the negative side, then disconnect the positive side.

3. Remove the battery from the engine bay.

4. Remove the negative and positive battery cables.

Note: The positive battery cables are tied into the main engine bay harness. If you’d prefer to not have to unwind and rewrap everything you can always just bypass the factor wires on the big terminals for the starter and alternator, and then splice new lines into the existing wires on the M2 connector, small terminal of the starter, and the solid white wire of the 3-wire alternator connector.

5. Cut 2 and 4 gauge wire a little bit longer than the distances between the following:

  • Negative battery terminal and the body.
  • Negative battery terminal and the transmission.
  • Positive battery terminal and the starter’s big terminal.
  • Positive battery terminal and the alternator’s big terminal.

6. Strip the ends of the wire from step 5. Use the Forney Crimping Tool to crimp on the appropriately sized cable lugs to the cables — applying heat shrink where the cable lugs and wires meet. Add the Heatshield Productsheat sleeve to the wire going to the starter.

Note: There is no need to solder anything, a good crimp will never come undone.

7. Cut the positive battery cable that will run to the alternator (where to cut depends on where you want to put the fuse), and crimp on cable lugs with heat shrink as before.

8. Cut the following wires on the M2 connector:

  • Solid Black
  • Solid White
  • Black with White Stripe
M2 Wires Color Coded
M2 Wires Color Coded

9. Cut a black 14 gauge wire a little bit longer than the distance between the starter’s small terminal and the M2 connector.

10. Crimp on a spade connector on one side — using heat shrink to attach heat sleeve. Then crimp the other end to the black wire with the white stripe on the M2 connector from step 8.

 

11. Cut two red 14 gauge wires a little bit longer than the distance between the ANL Fuse Holder and the M2 connector. 

12. Crimp one red wire to the solid white wire on the M2 connector, and then crimp the other red wire to the solid black wire on the M2 connector.

13. Cut the solid white wire on the top of the alternator’s 3-wire connector.

14. Cut a red 14 gauge wire a little bit longer than the distance between the ANL Fuse Holder and the alternator’s 3-wire connector.

15. Crimp the red wire to the solid white wire on the alternator’s 3-wire connector.

16. Bundle all of the red 14 gauge wires and crimp on a single cable lug to them.

17. Put in 100 Amp ANL fuse into Fuse Holder.

18. Connect all of the positive cable lugs to the appropriate locations:

  • Red 4 gauge from positive battery terminal to big starter terminal.
  • Red 4 gauge from positive battery terminal to ANL Fuse Holder.
  • Red 4 gauge from ANL Fuse Holder to big alternator terminal.
  • Red 14 gauge bundle (from M2 connector and alternator 3-wire connector) to ANL Fuse Holder.

19. Connect all of the negative cable lugs (and spade connector) to the appropriate locations:

  • Black 14 gauge from M2 connector to small starter terminal.
  • Black 2 gauge from negative battery terminal to engine bay body.
  • Black 2 gauge from negative battery terminal to transmission.

20. Double check all connections, clench your sphincter, and turn the key to test both the “accessory on” and “start” positions. If the everything works, congratulate yourself on a job you’ll probably never have to do again for as long as the car is in one piece.

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