Expert: Vern Bullock - 9/19/2008

Question
The GEN light on my 1970 Buick Wildcat suddenly started coming on after the car is turned off and the key removed from the ignition.  The battery is being drained as a result.  If I hook a charger up to the battery, the GEN light immediately comes on.  The battery charges, but drains again once the charger is removed.  Was thinking maybe the regulator has gone bad?  Anything else to check?

Answer
Hi Craig:
Your generator light should only come on for two reasons...

1. When the ignition switch is placed in the ON position

2. When the generator is not charging the battery

Now, if we examine these two issues, we should be able to narrow it down to the problem.

When the charging system is inactive, the regulator GROUNDS that wire, turning the light ON. When the charging system is active and the system has voltage, the regulator wire becomes charged with 12 volts, and feeds the bulb. When the bulb gets 12 volts on each side, the bulb will NOT illuminate, indicating a charge condition is present.

So, it could a bad alternator or alternator wire. This wire also runs to the ignition switch. The other wire runs to the Generator.

Also, you could have a bad ignition switch that is not shutting off. In other words, the ignition is stuff in the ON position and any lights or other electrical components that are activated by the ON position of the ignition switch is still running, and there by draining your battery.

Are there any other lights or indicators that wold indicate the ignition switch is still on? If not, then check the alternator wire and replace it.