Tech Tip: Coil Resistor

For those of you out there who own a 1956 or 1957 Thunderbird, this tech tip is for you. The coil resistor is a small, and often overlooked, component of your car's ignition system. The coil resistor receives the voltage from your battery and converts it to a level acceptable to your coil. The 1955 Thunderbird's were equipped with a six volt electrical system and this lower voltage was allowed to flow directly to the coil. A coil resistor was thus not needed on the 1955 Thunderbird.

If your coil resistor is not functioning, you will know it! Your car will not start or it will stop running. As this part is often left on the car until it fails, you may have a coil resistor that is pushing forty. Though this may seem to be a young age to some of you, a little "preventative maintenance" should be in order. A replacement coil resistor can be purchased for about $5.00 from most of the Thunderbird parts suppliers. If you own a concours quality car and intend to show your car in either the Primary Original or Senior Primary Original category, you will need to find an original style coil resistor. An original coil resistor can still be purchased through your favorite Thunderbird parts supplier, but the cost will be substantially higher.

The coil resistor is a rectangular part measuring approximately one inch in width by about three inches in length. The center of the coil resistor is made up of a porcelain type material and is surrounded by a metal shield. The coil resistor is mounted next to your coil. It mounts to the bottom of your coil bracket which is attached to the top of your intake manifold and stands straight up. There are two wires which attach to the coil resistor terminals. The top terminal of the coil resistor is connected to the wire coming from the ignition switch. The wire will be coming out of the main wiring harness. The bottom terminal of the coil resistor is connected to the wire which goes to the battery side of the coil. If you put a new coil resistor on your car, be prepared for the first time you operate your car with the new resistor. Your coil resistor will smoke and become very hot. This is normal for the first few times you drive your car with a new coil resistor. After the porcelain coating has burned off, your resistor will stop smoking.

Source: CTCC Tech-Tip Manual 1993-1997