The slightest difference in LED or supply voltage may cause the LED to light very dim, very bright, or even destroy. A series resistor will ensure that slight differences in voltage have only a minor effect on the LED’s current, provided that the voltage drop across the resistor is large enough.

Note: Ballast resistors are usually located bolted to the firewall if your distributor and/or coil is at the rear of the engine. If your distributor is located near the front or side of the engine in the case of an inline-4 cylinder, then it’s probably right near the ignition coil or distributor.

A quick and easy way to diagnose ballast resistor failure is to bypass it by running a temporary jumper wire from the battery to the coil. If it starts and remains running, you’ve found the problem. The ignition points are not designed to take full battery voltage for long.

if the vehicle is negative ground ….the negative side of the coil (-) is to the distributor. if the vehicle is positive ground then the (+) is connected to the distributor. CB means contact breaker. SW means ign. switch.

When a relay is off, the COMMON is connected to the NC (Normally Closed). The NO (Normally Open) connection of the relay is not connected until the relay turns on. When the relay turns on, the COMMON move from NC to NO. Mechanical relays create a Clicking sound that indicates movement o the COMMON terminal.

Automotive relays are typically 150-200mA (“72 ohm coil”). coil”). As I hint above, relay specs are typically given in coil resistance. Tim.

The relay draws 40 mA at 5V applied directly across it. It is the current required by the relay to operate.

The current draw of the coil is not normally shown but is typically 150-200 mA with a corresponding coil resistance of around 80-60 W. Tip: Knowing the coil resistance is useful when testing the relay for a fault with a multi-meter.