I've been going over my electrical system and discovered a couple of oddities. First off, at idle the voltage measured at the battery is 15.4-15.6. Doesn't change at higher rpms or by turning on accesories. Too high I think, so I replace the voltage regulator thinking its laying down on the job. I get the same measurements with the new VR as well. Okay. Now I'm thinking maybe I have a drain and the alt is just trying to charge the battery up (new battery btw) which explains the high voltage. I disconnect the battery negative cable and connect a multimeter beween the - post and the ground...starting at 0 the - reading builds slowly untill it reads @ -12 volts. Then I do the same test with just the voltage indicator light and it flares briefly and then goes out. Does it every time. Questions: Do I need to worry about frying something with the high voltage...and whats the deal if its not the VR's fault? Secondly, how do you interpret the results of the drain test? It seems that the multimeter indicates a drain and the simple light indicator does not. Why would it light up for a second then go out? Thanks for the help.

 

The meter needs very little current to make it read a voltage. The less current it takes, the better the quality of the meter. You are measuring very little current drain with the meter.

The test light takes a lot more current to burn, and thus is probably more suited for the test.

The charging system has a feedback wire that tells the regulator what the voltage is in the system. This wire is goes to terminal "A" on the voltage regulator. The wiring diagram shows this wire being spliced into a wire that leads to the starter relay post that goes to the battery. I would check this wire from terminal "A" all the way to the battery, and also check and clean the battery terminals.

I don't know if you have one of the types of batteries that you can check the water level, but if you can, and the water level is low, top it off and keep a check on it. If it keeps losing alot of water, this is a sure sign it's being overcharged.

Does it crank ok? If not, you may have a problem with the battery being a little low, and the charging system is trying to keep up. Having a high voltage is normal after cranking, but the voltage should trim itself back a little as the battery receives more charge.

 

Thanks for the feedback Franklin. I guess I shouldn't worry about a drain since it passes the test light. Although, why does it light for a second before it goes out? I suppose its fine since the light goes out but I thought this odd. I think the battery is a little low (which is why I suspected a drain) resulting in the higher voltage readings. I'll throw the battery on the trickle charger just in case and keep an eye on the voltage readings and water level. Good info, appreciate it.

 

I threw the battery on the trickle charger and it read fully charged. Now I'm puzzled. No drain, new battery fully charged, yet voltage with the truck running averages 15.5, too high. Readings remain the same with two different meters and between my new VR and my old one. Wiring harness between the VR/alt/solenoid also new and checks out. What gives?

 

What voltage do you get with the truck off at the battery?

 

This is a REALLY good read on batteries.

 

Franklin, it will read high, @13.5 before dissipating down to 12.5. Steve, I'll go read that link now, thanks.