I’ll make it quick. I’ve been running the Cadillac alternator. I have big 3 mod. I also have the harness adapter from alternator to oem harness. I’ve been running this alternator for few months. So the truck was sitting for a while. A week ago I started to drive the truck and the battery light came on. It stayed on for some time. Then went away. Kinda flickered. Kinda did it’s own thing. The scangauge read 12v and even 11.9 at point. I found the stud terminal on the alternator was lose. So I took apart and tightened it. Though that fixed the issue. I was driving it around and same issue happened. Battery light came on. Went away and it basically did it’s own thing. So that did not fix the issue. I started messing with the adapter and my harness. When I unplugged it it didn’t do anything. So for example. When the scangauge read 14v I unplugged the harness from the alternator. It did not change anything. Neither did the battery light came on. So WTF? Why and neither did the voltage reading change. However I did find 2 wires slightly missing insulation near the oem connector. So I was moving them around to see if anything changes and it did not. So my buddy warrantied the alternator for a new one. I replaced it. Now it reads 13.8 - 13.9 - 13.7. Couple times it dropped to 12ish for a second. Wtf is going on. How can I try to troubleshoot this ? I never had anything like this. And it’s like out of the blue. I did order a new harness adapter. But haven’t replaced it. And ideas how to look at this ? Maybe a bad battery?
Little help with my voltage situation please.
- Thread starter kolelt
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TheDurk
Elite Member
FYI--the light will NEVER come on with the alt. unplugged. It needs ground from the alt to come on.
I would verify your truckside connections. First, change your ALT-S fuse just for fun. It might be semi-fried, although unlikely.
Then, ground the yellow-green wire (original harness) with ignition on. BATT light should come on and off with ground.
The white (full-time) and red-blue (key on) wires should show full battery voltage.
I would verify your truckside connections. First, change your ALT-S fuse just for fun. It might be semi-fried, although unlikely.
Then, ground the yellow-green wire (original harness) with ignition on. BATT light should come on and off with ground.
The white (full-time) and red-blue (key on) wires should show full battery voltage.
I was go into tag you in this lol. Because you know your stuff. With that said. By ignition on. Do you mean start the truck ? Or ACC on? Should the battery light come on when you turn the key to before starting the truck. As in all dummy lights ? Then it goes away after starting. Correct ?
And when you say the battery light should come on and off. Like all at once. It will come on. Then go away?
TheDurk
Elite Member
key on is just that--not ACC, the one after, but without starting engine. If I wanted the engine running, I'd say that. Battery light should come on before start, then it goes out once alt excites and starts charging. It's different than some lights as it will stay on until start, some go out after a few seconds (ABS?, SRS?).
Ok. I will do this tomorrow and get back to you. Thank you
I will that I also stopped at autozone to get another test done. Everything read good. Even with everything on. However my girlfriend was inside and said the battery light came on for split second then went away along with the volts dropping. But the test on battery, alternator were good.
TheDurk
Elite Member
I think you said you have the Big 3 to go with your 10SI. Still, I think you should pull your battery terminals, clean and reinstall. You can find things this way you can't any other way. I once found a new terminal that had been overtightened by some clown and the bolt was stripped just at the point where it needed to tighten. It looked perfect in place, but once you tried to reinstall it, it was clear it would not get tight. Pull your fender and engine grounds, clean and reinstall for same reason. Don't say, "Ah, they're new, no reason." Something is wrong somewhere, so make no assumptions.
@the durk
What is ALT-S function? Because I just checked that fuse. 7.5 amp and it was blown. I just replaced it. I did not get to do the other tests yet. As I feel like this might have been my issue !? The blown fuse could have been caused by the older alternator. When it had the lose stud that the positive wire attaches it. The lose stud could have shorted out something this poping the fuse and I did not know this.
I’ll try and do the tests you recommend just to make sure. Hopefully this bad weather doesn’t take over !
What is ALT-S function? Because I just checked that fuse. 7.5 amp and it was blown. I just replaced it. I did not get to do the other tests yet. As I feel like this might have been my issue !? The blown fuse could have been caused by the older alternator. When it had the lose stud that the positive wire attaches it. The lose stud could have shorted out something this poping the fuse and I did not know this.
I’ll try and do the tests you recommend just to make sure. Hopefully this bad weather doesn’t take over !
So I just did the tests you mentioned before.
I grounded the yellow-green wire with ignition ON and the battery light was. “On” if I removed the clamp from ground. The battery light was “off”
Red-blue wire showing 12.13v with ignition on ON
White wire is showing 12.72 with ignition off.
9.8 resistance on Red-blue wire.
There was 0 resistance on the other 2 wires.
I grounded the yellow-green wire with ignition ON and the battery light was. “On” if I removed the clamp from ground. The battery light was “off”
Red-blue wire showing 12.13v with ignition on ON
White wire is showing 12.72 with ignition off.
9.8 resistance on Red-blue wire.
There was 0 resistance on the other 2 wires.
At idle with everything off including AC. The scangauge is reading 13.7 min and 13.8 max. KLEIN MM400 at battery is showing 14.8v steady.
At idle with every single accessory ON including AC, high beams, blinkers, rear defroster, led lights and such. When AC is not kicked on the scangauge is reading 12.4 min and 12.5 max. Scangauge showing 13.6 min and 13.8max when AC kicks on. The multimeter at battery is 12.76 min and 14.23max ( with AC off the multimeter is showing 12.82v at batt. 12.74min and 12.81 max )( with AC on the multimeter reads 14.19 max )
At idle and just AC on. Scangauge showing 13.7 min and 13.8 max. The multimeter is showing 14.2min and 14.19max ( fluctuating around 14.17-14.19)
At idle with every single accessory ON including AC, high beams, blinkers, rear defroster, led lights and such. When AC is not kicked on the scangauge is reading 12.4 min and 12.5 max. Scangauge showing 13.6 min and 13.8max when AC kicks on. The multimeter at battery is 12.76 min and 14.23max ( with AC off the multimeter is showing 12.82v at batt. 12.74min and 12.81 max )( with AC on the multimeter reads 14.19 max )
At idle and just AC on. Scangauge showing 13.7 min and 13.8 max. The multimeter is showing 14.2min and 14.19max ( fluctuating around 14.17-14.19)
TheDurk
Elite Member
I assume BATT light stays off? So, at the moment all looks normal. As far as the ALT-S fuse, if that is blown, the alt. will ramp up its charging to max regardless of load or battery stat-of-charge. Not a good thing....
Yes. The battery light stayed off during all the load tests. Do you think it’s ok for red-blue wire to have resistance of 9.8?
I was driving with the alt-s fuse blown for couple days. Decent amount. You think anything got messed up ?
Although I would of though the Cadillac alternator 140amp would idle at way more than 13.7-13.8v.
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phattyduck
Elite Member
Charging voltage is dependent on temperature. 13.7-13.8V is NORMAL in warm weather, and especially so after the engine bay is heated up. It should only be over 14V when cold (cold weather, I mean, not just engine hasn't been started in a while). The voltage regulator has temperature compensation to keep from overcharging the battery.
-Charlie
