In 1955, the electrical system of the Thunderbird was 6 volt positive ground. If your Thunderbird is a 1955, with a 6 volt, positive ground system, the battery resting voltage is 6.3 volts and the charging voltage should be about 7.1 volts. The exact charging voltage may be as low as 6.6 volts or as high as 7.3 volts.
Take a multi-meter and set it to measure DC voltage, then measure the voltage across the positive and negative battery terminals with the engine off. On a 6 volt system, a fully charged battery should read a resting voltage of 6.3 volts. After you start the car you should see a charging voltage of about a volt higher than resting voltage. If the reading doesn’t increase by about a volt or if it stays at the resting voltage, it means that the alternator isn’t recharging the battery. This could be because the battery is defective, alternator is defective, the regulator is defective, or the wiring between them has failed.
With the engine running, if the generator light stays on at full brilliance, you have no voltage at the voltage regulator terminal that goes to the armature. The armature is acting like a dead short and that causes the bulb to glow. This is why the generator light is on before the engine is running.
If the generator light glows dimly or flickers, the voltage at the armature is low. Sometimes this is caused by low engine RPM. If the light goes out when you accelerate it could be normal or your voltage regulator might need adjustment.
Another cause of a generator light glowing dimly or flickering could be a poor ground somewhere. This will often reverse the current through the dash light in
search of more ground. Another cause is the generator. The brush springs are not strong enough or the brushes are sticking in the holders.
A basic charging system health test: Use a multi-meter to measure the resting and charging voltages as described above. Then, with the engine running, gradually increase the electrical load by turning on the headlights and the blower fan. Then increase the engine RPM to about 2,500 as you watch the reading on the multi-meter. If the voltage stays about a volt higher than resting voltage, then the car’s charging system is functioning. But if the voltage drops or increases dramatically at any point, there’s a problem with the alternator or the voltage regulator.
doug7740
1955 Thunderbird Blue
