Alternator question

I'm trying to find a "sneak" circuit that seems to cause my battery to discharge. The motor is not yet ready to run; I am just proving out the cars wiring.

With both battery cables DISCONNECTED,and the ignition key off, I measure 1.4 ohms of resistance between the two cables. With the key on, 4.7 ohms. Again with the key off, when I disconnect the D+ (61) terminal from the alternator, I measure infinity between the two cables.

Would someone please unplug the D+ wire from their alternator and measure the resistance from that terminal to the case of the alternator?

Does anyone have a schematic of the voltage regulator that is internal to the alternator?

The alternator in question is a two wire unit with a built-in regulator. The only terminals are B+ and D+(61).

What you're measuring is probably the resistance of the alternator "charge" bulb in the dash, which is on the other end of the D+ lead. One side of that bulb goes to the D+ connection on the alternator, and the other side of that bulb is connected to the battery + side via the ignition "on" circuit.

The D+ alternator lug is connected to a winding in the alternator body. When the alternator is working, it uses the D+ as a reference voltage coming from the battery + side through that bulb to regulate the amount of charge needed to bring the battery up to 13.6 volts.

Make sure your dash bulb is connected to the "on" side of the ignition switch, not directly to the battery.

You may still see some resistance through that bulb, but the way the alternator works it shouldn't discharge the battery.

gn

Gordon...thanks for the response. I know how it's supposed to work; I'm just trying, by elimination, to find what is probably a mis-landed wire. See the SOC LIBRARY section, Speedster Wiring, Dwg#1 for my diagram that includes the circuit in question.

The only correction I've made to the wiring shown there is to move the brake light ckt from fuse 4 (always hot) to fuse 9 (switched by ignition sw). Short of actually running the car, everything else on the four page diagram seemed to operate properly. Once I find this last remaining problem, I'll update the four drawings and send them to Theron to update those in the library.

Again, if anyone knows of a schematic of the 2-wire alternator with built-in regulator, I'd like to include that on my diagram.

I am pretty sure brake lights are always supposed to be able to work. I personally would move that one wire back, it may actually be in the MV codes.

My brake lights only work with the key on.

Danny...The reason I moved the brake lights to the switched fuse is that NJ wants to see a BRAKE WARNING light on the dashboard. This is to function off of the pressure switches on the master cylinder, and off of a switch that detects the e-brake. The e-brake handle opens a N.C. limit switch in the down (released) position. When pulled up, it turns the light on. Obviously not a good thing on an unswitched circuit when you park the car.

See bottom of the page of drawing #2.