Battery light comes on when glow plugs engage

Figor

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My truck has been slow to start. Batteries seem weak. The batteries are a year old. I took them to be replaced under warranty and was told they are still good. The battery light comes on when the wait to start light is on. Didn't do this when batteries were new. It goes out after truck starts, if it starts before the batteries go dead. Alternator is charging fine. Any suggestions?
 

DaveBen

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Check your alternator. Sounds if it isn't charging the batteries. You should see 13.4 volts when running, or more.
 

YJMike92

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The battery light should be on with the key on and the engine not running. Are you sure the wait to start light is involved?
Are the battery cables tight and corrosion free?
 

Figor

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The alt is charging. And cables are clean and tight. I seemed to think the battery light comes on when key is cycled but goes back off?

It stays on for the duration of the wait to start light and then goes out with the wait to start light.

Something's definitely dragging the batteries down. Maybe it's the starter. Or the guy that tested them is feeding me a line.
 

Cubey

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Check the cable insulation futher down.

Batteries can test "good" but be too weak for IDIs. I had that issue. They tested good at one store. I had them tested again at a different store and one came up "replace soon". I had no receipt for them so even though they were within the free replacement period, they couldn't honor it. They were oreilly batteries in the F250 when I bought it. I bought a new pair of Walmart maxx 65N batteries (not 65S, they have lower CCA) and that solved my weak low batteries.
 

YJMike92

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The alt is charging. And cables are clean and tight. I seemed to think the battery light comes on when key is cycled but goes back off?

It stays on for the duration of the wait to start light and then goes out with the wait to start light.

Something's definitely dragging the batteries down. Maybe it's the starter. Or the guy that tested them is feeding me a line.


The battery light should stay on as long as the key is on engine off. The starter could be the culprit. Does it spin over good with a jump?
 

Figor

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I haven't tried jumping it. I've been testing voltage at the passenger side because drivers side has the air intake over the positive post. I get 13.62 on the passenger side. Decided to check the drivers side. I'm only getting 12.45 here. I'm kinda scratching my head now. How can it only charge one side?
 

YJMike92

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You will have to isolate the batteries and test them separately. If they are hooked together the test will not be accurate.
 

DrCharles

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The test he's doing (for voltage while the alt is running) is not affected by the batteries being paralleled. There may be a slight difference if one is drawing more current than the other. Slight. Not 1.17 volts!

Figor, you have a bad connection somewhere at the batteries. Try measuring every junction: each post to its terminal, terminal to wire, wire to ground bolt, that bolt to frame, etc. You will find it quickly. May even be able to feel warmth at the bad spot.
 

KYSlowhand

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I haven't tried jumping it. I've been testing voltage at the passenger side because drivers side has the air intake over the positive post. I get 13.62 on the passenger side. Decided to check the drivers side. I'm only getting 12.45 here. I'm kinda scratching my head now. How can it only charge one side?
Check ground cables - OHMs high resistance indicates bad cable
 

YJMike92

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The test he's doing (for voltage while the alt is running) is not affected by the batteries being paralleled. There may be a slight difference if one is drawing more current than the other. Slight. Not 1.17 volts!

Figor, you have a bad connection somewhere at the batteries. Try measuring every junction: each post to its terminal, terminal to wire, wire to ground bolt, that bolt to frame, etc. You will find it quickly. May even be able to feel warmth at the bad spot.

I guess I misread the post. I was thinking the batteries were tested while still hooked together which they may have been.
The best way to test an operating circuit is with a voltage drop. Very easy (google it for details) Anything more than .5 volt is an issue.
 

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