Warning Lights Stay on, car works fine

[martyg]

I have a 1985 300SD. The warning light for the Battery stays on all the time. The battery is new. The alternator is charging to 13.5- 13.8 volts. The Antilock and low fuel warning lights come on intermittently, off if I am accelerating, on if I am coasting. The Brake light and brake warning lights are dim, they go off after I start driving, however, they come back on dimly if I coast. The car seems to run fine. This problem started during a rain storm. And has continued for a couple of days. Any Ideas?

[nhodges]

Bad Ground.

[86560SEL]

Also too, be sure your battery cables are clean and have good connections.

[martyg]

Thanks for the reply.
I've cleaned the battery terminals, and the ground at the battery and body of the car. The warning lights are still on. Is there a ground for the warning lights? Where?

[stevebfl]

The circuit for the alternator light is rather simple although the internal circuitry of the dash is full of diodes that can complicate matters.

Generally speaking power from term 15 ignition goes through the light bulb to the 61 term of the alternator. This power goes through the regulator, through one brush through the armature through the other brush to ground lighting the light with key on engine off. When the alternator turns and power is generated the trio diode pack feeds power from the output to the same 61 term input. The regulator then regulates the current flow through the armature but the light now has battery voltage on both sides of the bulb filament and thus the light goes out.

If the light is on there is a voltage across the bulb. To just glow at night this only needs to be a volt or two. The voltage regulator can cause this also. Resistance in either side of the circuit will lower one side of the circuit.

[martyg]

Since the alternator light, the antilock and the low fuel lights are all on does it narrow it down?

[whunter]

The alternator or voltage regulator is bad.
Have a great day.