Glow Plug Information

This information was sourced from - "Winter Starting Tips" article and even though it related to VW diesels the information is fairly similar to all .

Two types of glow plug circuits were used on early and late model vehicles.

1. The slow glow system was installed on early production vehicles;
2. The fast glow on late production vehicles.

Always refer to the relay number for proper identification.

An incorrect match of fast glow relay and slow glow plug will result in premature failure of glow plug and/or relay.

To quick check the system, check the amount of current that is flowing to all glow plugs. A good specification to remember is fast glow plugs pull 12 amps each and slow glow plugs pull 9 amps each.

Listed below are some guidelines to refer to when checking fast glow plug systems.

• 48 amps - all glow plugs are operating correctly.
• 36 amps - one glow plug is defective.
• 24 amps - two glow plugs are defective.
• 12 amps - three glow plugs are defective.
• 0 amp - all glow plugs are defective.

For slow glow systems use the following amp rating to test:

• 36 amps - all glow plugs are operating correctly.
• 27 amps - one glow plug is defective.
• 18 amps - two glow plugs are defective.
• 9 amps - three glow plugs are defective.
• 0 amp - all glow plugs are defective.

The above specifications are applicable to four-cylinder applications. If you have more than four glow plugs, just add 12 amps for each fast glow plug and 9 amps for each additional slow glow plug.

NOTE: Depending on outside temperature, you may experience a surge of current up to 140 amps.