Battery only showing 10 volts

[Mythic]

If the new battery registers 10 volts without the vehicle running then you might want to take a DVOM and check for resistance, shorts and fouled grounds. A new battery should read 12-13 volts with the KOEO. It should read 13+v with KOER. It sounds like you have a fairly heavy parasitic drain or maybe even a very light short to ground. Check the positive cable going to the starter. Many times they become loose and short out on the manifold or frame. A simple way to check is to turn the DVOM to resistance and hold one test lead on the positive terminal and the other on the rear engine ground strap. If you get anything other than OFL you have a short to ground somewhere. You can check the alternator by simply removing the negative battery cable while the engine is running. If it dies then your alt is the problem. If it doesn't then you probably have a fouled connection somewhere.

Hey Tempted, could you clarify all of the abreviations for me? I am not really sure what you are telling me. Thanks for your help, I really appreciate it.

 

[Tempted]

Hey Tempted, could you clarify all of the abreviations for me? I am not really sure what you are telling me. Thanks for your help, I really appreciate it.

Sorry about that. DVOM is an abbreviation for digital volt ohm meter(multimeter), KOEO is Key On Engine Off, KOER is Key On Engine Running, OFL is simply infinite resistance(no measurable continuity).

okay, I just put the voltmeter on the battery while running, registered 13.8. Alternator was registering 14.2 while idling. I don't know the idle speed, there is no tach in my truck.

Once again, I want to say thanks for all of this help.

Should I just take the alternator off and go have it tested at an autoparts store?

Alright those readings show the alt is at least producing voltage at idle. Now you want to check throughout the RPM range. Clip the meter leads to the battery and rotate the throttle plate. If the volt reading changes significantly then you might have an issue. If it stays between 13 and 15 volts you are fine. Now, if you determine the voltage is holding well, turn on as many accessories as you can. Heat, bright lights, radio, interior, etc. Check the voltage. If it is below 12, you have an amperage issue meaning the alt might hold the volts but it can't produce enough amps. Similar to overloading a self contained generator. After the draw exceeds the output, the generator shuts down.

Now, one thing to watch for, if any one of your accessories single handedly drops the voltage to below 12 you might have a short in that circuit. What I mean is if you turn only the lights on and the volts go down excessively but if you turn only the heater on and they don't, there might be a short in the light circuit somewhere.

Hope that helps.

 

[GMCTRUCKS]

From what I was learned one should always slow charge a battery when it goes dead meaning a slow charge at 2 amps. What I did is I bought this volt meter that connects to the cig lighter I just wanted to have it like example to read my volts when at idle because I have under drive pullleys. I say you have a bad alternator and check all your wiring make sure all the wires are connected in the right places.

 

[Tempted]

What I did is I bought this volt meter that connects to the cig lighter I just wanted to have it like example to read my volts when at idle because I have under drive pullleys.

Your truck doesn't have a volt gauge?

 

[Mythic]

Tempted, thanks. That totally clears everything up. I am going to take the alternator off and go have it tested.

Do these trucks have a voltage regulator? Because I think it's odd that the voltmeter on the battery shows the battery is good and the voltmeter on the alternator shows it is good, but the volt gauge in the dash shows less than 10 volts.

Thanks again everybody for the help.

 

[Tempted]

Does the gauge on the truck fluctuate when you turn accessories on? If you are getting a totally different reading from the multimeter to the cluster gauge then I wouldn't remove the alternator just yet. The needle might be sticky/stuck or the circuit might have grounded out.

 

[Mythic]

Tempted, I just got back from having the alternator tested. It passed. I picked up a replacement voltage regulator, just on a hunch, but I have no idea where it goes. Is it actually built into the alternator? Is it external?

Tempted, yes, the gauge fluctuates when I turn accessories on. It goes from reading 10 volts to less than 9 volts. Where would I look to check out if the circuit is grounded out? Which circuit are you refering to?

Please help!!!!

Thanks guys.

 

[MOBS]

It'll go on or in the back of alternator. If it's an external voltage regulator, there should be I think 3 screws, or tabs holding it in the back.

 

[Mythic]

Hey Mobs, do I need to take the alternator apart to access it? I am not seeing anything externally.