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Re: No battery light on '84 900 Posted by Ari [Email] (#2847) [Profile/Gallery] (more from Ari) on Tue, 29 May 2001 16:09:06 In Reply to: No battery light on '84 900, Dietrich, Tue, 29 May 2001 13:59:30 Members do not see ads below this line. - Help Keep This Site Online - Signup |
The battery light has two connections - one goes to the battery positive post, and the other connects through a thin wire to a post on the Voltage Regulator.
Some background - an generator has permanent magnets - the magnetic field is there even with power off. An alternator has electromagnets to creat a field - no power, no magnetic field. You need some voltage to create this magnetic field in order for the alternator to produce voltage - a 'jump start', as it were. When you turn the car to ON but don't start the car, current flows from the battery, through the light (turning it ON), and into the voltage regulator. The regulator pushes this current through the field coils in the alternator, creating a magnetic field. When you start the car and the alternator starts spinning, it creates voltage, and the voltage regulator uses this voltage to drive the field coils. Since the alternator is producing voltage, you get 12 volts (or so) on both sides of the battery light (battery voltage on one side and alternator on the other). No current will now flow through the bulb, and it goes out.
So what? Since your battery light is out, that means that the current isn't flowing from the battery into the voltage regulator, a voltage that the alternator needs to get started. So make sure you've got battery voltage on one side of the battery light, and make sure the other side of the light is attached to the voltage regulator. There is supposed to a thin wire on the back of the voltage regulator - did it get hooked up, and did it get hooked up correctly? If you disconnect it from the alternator and touch it to ground (this is the THIN wire, not the battery wire!!!), the battery light should come on with the key at ON. If not, check the wiring. Next - is the alternator properly grounded?
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