Re: BATT Light on Instrument Cluster stays on with car off

Posted by HH56 On 2016/7/13 22:04:21

Excellent observation. The battery voltage is being fed backward thru the bulb causing it to light.

With the cutout stuck closed, voltage that is normally not there except when the generator is charging is present on the GEN or ARM terminal of the regulator. One side of the bulb is connected to that point. Voltage feeds back thru the bulb to the junction at ign switch. With the ign switch off it finds ground by going in series thru another component connected to the same terminal and you have instant light.

In this case, if there were enough voltage left in the battery turning the ign sw on should extinguish the light because equal voltage would again be present on both sides of the bulb. It would act the same as when the car is working normally except the light is opposite to what is expected. Without an ammeter you would never know there is a problem. If it were an LED bulb you would not have the light on because those can't function with reversed polarity so you would just have the dead battery.