How to Hook Up a Ballast Resistor

A ballast resistor is an electrical device designed to lower ignition voltage after a vehicle engine is started to help prevent wear on ignition system components. Power to the engine starter motor bypasses the ballast resistor during starting to increase ignition voltage to the coil. After starting, the ballast resistor reduces the current to the coil to prevent it from overheating. You can hook up a ballast resistor with a few tools and basic do-it-yourself skills.

Adjustable wrench
Drill
Drill bit, 1/8-inch steel
Phillips screwdriver
Flat-head screwdriver
Vehicle service manual
Wire cutters
Wire strippers
Stranded 16-gauge insulated wire
Crimp connectors, 16 gauge
Crimping pliers
Electrical tape

Instructions

- 1
  Disconnect the negative (-) battery cable from the battery. Loosen the cable clamp nut by turning it counterclockwise with an adjustable wrench. Twist the cable clamp in either direction while pulling it upward.
- 2
  Drill a mounting hole for the ballast resistor using a drill fitted with a 1/8-inch steel drill bit. Choose a position for the hole on the vehicle’s firewall or other location where the resistor will be free from other components.
- 3
  Mount the ballast resistor using a metal screw. Tighten the screw clockwise with the appropriate screwdriver.
- 4
  Locate the engine ignition coil. The coil has three terminals: one positive (+), one negative (-) and one large terminal that delivers high voltage to the system. Refer to your vehicle service manual if necessary.
- 5
  Cut the wire from the positive terminal of the coil as close to the ballast resistor as possible using wire cutters.
- 6
  Strip 1/4 inch of insulation from both ends of the severed wire using wire strippers.
- 7
  Cut two lengths of 16-gauge stranded wire sufficient to reach the ballast resistor from the severed coil wires.
- 8
  Strip 1/4 inch of insulation from one end of each wire and 1/2 inch from the other end of the two wires.
- 9
  Connect the two lengths of 16-gauge insulated stranded wire with the 1/2-inch stripped ends to either terminal on the ballast resistor. Twist the ends of the wire into a loop, keeping the open end of the loops to the right. Tighten the terminal nuts with the adjustable wrench.
- 10
  Insert the 1/4-inch stripped end of the positive wire from the coil into either end of a 16-gauge crimp connector, and compress the connection using crimping pliers. Connect either wire from the ballast resistor to the other end of the crimp and compress the end with the pliers.
- 11
  Connect the other end of the severed coil wire to the remaining wire from the ballast resistor following the procedure outlined in step 10.
- 12
  Wrap the crimp connections with electrical tape.
- 13
  Reconnect the negative cable to the battery. Tighten the cable clamp nut clockwise.

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