Article by Mike Croke.
Due to the fact that most of those who are performing a battery relocation are likely to be drag racers, the following article shows how to do an NHRA legal install. Road racing sanctioning bodies are likely to have slightly different requirements, so consult the rule book of your particular sanctioning body to be sure of your legality.
From the NHRA rulebook:
All batteries must be securely mounted and may not be relocated into the driver or passenger compartments. Rear firewall of .024-inch (.6 mm) steel or .032-inch (.8 mm) aluminum (including package tray) required when battery is re-located in trunk. In lieu of rear firewall, battery may be located in a sealed .024-inch (.6 mm) or .032-inch (.8 mm) aluminum, or FIA accepted poly box. If sealed box is used in lieu of rear firewall, box may not be used to secure battery, and must be vented outside of body. Strapping tape prohibited. A maximum of two automobile batteries, or 150 pounds (68 kg) combined maximum weight (unless otherwise specified in Class Requirements) is permitted. Metal battery hold-down straps mandatory. Hold-down bolts must be minimum 3/8-inch (9.53 mm) if battery is relocated from stock and other than stock hold-downs are used ("J" hooks prohibited or must have open end welded shut.).
8.4 MASTER CUTOFF
Mandatory when battery is relocated, or as outlined in Class Requirements. An electrical power cutoff switch (one only) must be installed on the rearmost part of each vehicle and be easily accessible from outside the car body. This cutoff switch must be connected to the positive side of the electrical system and must stop all electrical functions including magneto ignition. The external control switch for this cutoff switch will be clearly indicated by a red flash inside a white-edged blue triangle with a base of at least 12 cm (see drawing 25). The positions must be clearly indicated with the word "OFF". If switch is "push/pull" type, push must be the action for shutting off the electrical system, pull to turn it on. Any rods or cables used to activate the switch must be minimum 1/8-inch (3.2 mm) diameter. Plastic or keyed switches prohibited. Switches and/or controls must be located behind rear wheels on rear engine dragsters. "
To meet the requirements, the disconnect switch must stop all electrical activity and kill the engine. Since there are two sources of electrical power in the car (battery and alternator), the switch must disconnect both. This will require running the alternator's output back to the disconnect switch to the same side as the battery's positive terminal.
Moroso polyethylene sealed battery box (~$90 from Summit Racing)
- Flaming River Remote Battery Disconnect (~$82 from Summit Racing)
- 30 feet of 00 gauge of welding cable (purchased from local US Air Weld for about $1.30/foot)
- 20 feet of 4 gauge battery cable (~$.30/foot from NAPA)
- 4 copper lugs to fit onto the 00 gauge welding cable (NAPA)
- 2 copper lugs to fit onto the 4 gauge battery cable (NAPA)
- 6 insulated cable clamps to secure cables to underside of car (NAPA)
- Heat shrink for 00 & 4 gauge cables
- Marine style battery terminals (crimp onto battery post and have studs with wing nuts to remove battery cables)
- Begin by disconnecting and removing the stock battery and tray from under hood. Looks better already, doesn't it?
- Test fit the battery in the new Moroso box. There must be enough room on the sides for the hold down bolts also.
- Raise car and support on jack stands.
- Remove all carpet/sound deadener from hatch area on passenger side behind rear axle.
- Drop gas tank approximately 1 foot on passenger side so that you can't drill a hole in the top of it while mounting the battery box. This is also needed to gain access to the nuts that will secure the entire battery box to the floor.
- Position the Moroso battery box as desired and drill two holes through the box and floor. Caution: Do not drill through the gas tank! Also, note that depending on where the box is located, the mounting holes might be positioned over frame rails or other inaccessible areas. Verify where the drill will come out the floor under the car. Remember that there are large fender washers that must fit over the hold down bolts so the hole can't be too close to anything. Leave enough room for the battery to fit between the hold down bolts.
- With the holes drilled, insert the hold down bolts through the holes and through the battery box. Install the fender washers and nuts under the floor to secure the bolts.Make sure that the bolts don't sit so high that they interfere with the battery box lid.
- Install the battery in the box and secure with the cross plate and hold down bolts.
- This takes some thinking about where the switch should go. It has exposed terminals and the actuating linkage must work freely. I mounted my switch to the side of the battery box. See the pictures at the lead of this article. My push rod for the switch goes through a small hole between the license plate and taillight. I used a wing nut and bolt so I can remove the push rod when not at the track.
- Secure the switch to the supplied bracket.
- Begin by removing the original stock battery cable from the positive battery terminal to the starter solenoid. Discard this cable.
- Strip about 1/2" from one end of the 00 gauge welding cable.
- Take one of the large copper lugs and place in a vise with the cable end up. Using a propane torch, heat the copper lug and fill with electrical solder until the lug is almost full. Keeping heat on the lug, insert the stripped end of the welding cable into the copper lug. Continue applying heat until the solder wicks up into the cable. [Although the lugs can be crimped, this method guarantees a superior electrical connection that can't pull loose.] Allow to cool. Cover with heat shrink but don't cover hole in lug.
- On the driver's side of the hatch floor, there is a grommet just over the frame rail. It may be necessary to move the plastic interior piece to see it. It will be between the shock towers and close to the driver's side shock (but on the floorpan). Feed the non-lug end of the welding cable down through this grommet and out the opposite hole in the bottom of the frame rail.
- Route the cable forward under the car. Keep the cable away from exhaust, suspension, etc. Use the insulated clamps to secure the cable to the floorpan. Keep enough cable inside the hatch area to cleanly route the cable to the disconnect switch.
- Route end with lug to disconnect switch. Doesn't matter which side at this time.
- At the front of the car, bring the cable to the starter solenoid and cut to length. Install a copper lug similar to the first one, cover with heat shrink, and attach the lug to the starter solenoid.
Alternator Output Wires
Fox cars with stock alternator - find the large plug with the 2 heavy gauge black/orange wires. Cut the black/orange wires about 6" from the plug. Insulate the wires that go to the harness on the car (the blue heat shrink just right of the oil filler neck in the pic). Connect the black/orange wires coming from the plug to one end of the 20' 4 gauge battery cable. To do this, I soldered a lug onto the 4 gauge battery cable, crimped a large ring terminal to the black/orange wires, and used a bolt and nut to secure them to each other. The entire connection is then covered with heat shrink (as shown in the picture coming from the original plug on the alternator).
On cars with the 3G alternator - there is only one large black/orange wire. Remove this wire from the alternator and insulate. Solder a lug onto one end of the 4 gauge battery cable and attach the lug to the output post on the alternator.
Final Cable Routing
- Route the 4 gauge battery cable to the back of the car and route into the hatch area. Secure under the car with insulated clamps.
- Solder a lug onto the end of the 4 gauge battery cable and attach to the disconnect switch on the same post as the 00 gauge welding cable.
- Attach the stock original positive battery cable to the empty post on the disconnect switch. Route the other end into the battery box. DO NOT CONNECT TO BATTERY YET!
- Using leftover 00 gauge welding cable, make a ground cable to reach from negative battery terminal to good frame ground. Do not use the floorpan. Use a bumper bolt, quad shock bolt, etc. Be sure to scrape off any paint, undercoating, etc. before attaching. Route away from suspension and exhaust.
- Attach a 4 gauge ground cable from the engine block to the front frame rail. This will be the principal ground path for the engine so ensure that the connections are clean.
- Make sure disconnect switch is in off position. Attach ground cable to battery negative post. Attach stock original positive battery cable from disconnect switch to positive battery terminal.
- Start the car. Check the voltage at the battery. It should be more than 12.8VDC indicating the battery is charging. Rev the engine to verify the voltage climbs over 13VDC.
- With the engine running, turn off the disconnect switch. The car will die. Success!