batt drain help. (alt)

[VetteVet]

Originally Posted by TwoFiftyShifter

I had this a couple months ago

Changed the voltage regulator. $22. All fixed.

The cool Voltage regulator test is to pull the positive battery cable WHILE the truck is idling. If the truck stays running, the voltage regulator is fine

A battery drain is nothing more than a current running through a load whether its through a light left on or a sticking relay in the horn relay or voltage regulator. In your case it was the voltage regulator.

Pulling the battery cable is not a valid test of anything. It will only show that the alternator is putting out enough voltage (current) to keep the engine running. What it will do is throw the alternator into an unregulated state, because the voltage regulator can no longer sense the state of charge of the battery. Usually the alternator will default to full output based on the engine
RPMs. Any sensitive electronics like a distributor (HEI) module could be damaged.

The best test for a battery drain is to place a multi meter between the disconnected negative battery cable and the negative battery terminal with the multimeter on the 10 amps scale and with the engine off, and everything turned off on the vehicle. This test should be done with a fully charged good battery to avoid any internal shorts in the battery itself.

If the meter reads more than 3 or 4 milliamps .003 amps, that is unacceptable in most cases. If there are hacked up harnesses or added circuits by the OP then all bets are off.

Most all these drains are key off, and in the voltage hot all the time, loads. I/E. the alternator, the regulator if external, the horn relay (if the horn is disconnected, it would be blowing otherwise and obvious).

The procedure is to start disconnecting along the positive path of the trucks circuit. One at a time and leave them disconnected in case there is more than one draw.

Starting with the alternator, then the external regulator then the horn relay etc. until the multimeter amp draw drops to near zero. You can also use a test light, watching for it to dim or go out.

Memory items like radio presets will draw a small amount so the reading may not go to zero. It sometimes occurs when the owner has wired in a stereo system and has connected it to a hot positive source without a switched off capability.