Bypassing A Ballast Resistor

Many cars from the 1970s onwards would have been factory fitted with a ballast resistor. Simply put, a ballast system splits the usual 3 ohms resistance between the coil itself (1.5 ohms) and an external resistor (1.5 ohms). During starting, this resistor is bypassed, meaning the vehicle gets more spark energy because there is only half as much resistance in the ignition circuit. You can find more information about ballast resistors by viewing our article, or our video at the bottom of this page. This post is about removing or bypassing a ballast, which sometimes needs to be done if you are changing your ignition setup.

Why Bypass or Remove the Ballast Resistor?

Many people like to opt for a ‘high energy’ system, which utilizes a low resistance coil (< 1 ohm). This system is incompatible with a ballast resistor so in this instance, it needs to be removed or bypassed. Others may wish to remove a ballast for simplicity’s sake. You may also wish to remove it if you suspect the resistor has begun to break down or fail, but bypassing is a good option for when it’s built into the loom and tricky to remove.

Here are the basic steps for removing or bypassing a ballast:

1. Identify if the vehicle has a ballast resistor

This can either be done by a visual check or using a multimeter; ballast resistors can take two main forms, you are looking for a ceramic block, often mounted to the coil but sometimes elsewhere like the inner front wing, or a resistive wire coming from the loom. It will be wired between the ignition switch and coil +. If you can’t tell simply by looking at it, then please refer to our ballast test below:

2. Decide whether removal or bypassing is the best option

Whether you remove or bypass the ballast is entirely up to you. Removal is best if the resistor is easy to get at, but if it’s going to cause issues removing it then a simple bypass wire will do the job.

3. Removal or bypass

There are a few methods for doing this, so you will need to decide which is the best for you.

Removal

This is simply taking the ballast out and running an ordinary feed wire via the ignition switch to coil +. This is the simplest solution but it’s not always practical. If you can, join up the 2 wires that were going through it, or you can run a new wire entirely.

Bypass

• Switched 12V feed to + side of coil

This can be done by running a wire from somewhere like your fuse box and attaching it to the + of the coil.

• Wire between + and – of ballast resistor

If it’s a ceramic type, see attached pic for easy way to do this. It leaves all factory wires in place so it’s easy to convert back and makes it obvious to future mechanics that the resistor is bypassed. The bypass wire needs to be 1.0mm² 8 ohm.

What to do now that you’ve taken the ballast out of the system

Now that you have taken the 1.5 ohm ballast out, you will need to change the coil to suit whatever system you have installed. This may mean going back to a standard 3 ohm coil, or you may have the high energy system and require a high energy coil. The Viper coil is an ideal upgrade, whichever system you have, so head over to simonbbc.com to browse our selection.