It’s not idling too low is it ?
Pretty quiet in here... what are you working on? (11 Viewers)
- Thread starter Stumpalama
- Start date
This site may earn a commission from merchant affiliate
links, including eBay, Amazon, Skimlinks, and others.
It’s possible. When I flick on the AC it really struggles at idle. Doesn’t stall out but it definitely struggles and shimmies. The 14.4 volt was at idle however, and the battery with ignition off was about 12.5. But the lights go out when I’m getting the rpm up.... could be.
Stumpalama
Forum Junkie
Stumpalama
Forum Junkie
- Thread starter
- #4,424
Lights are dimming and brightening when idling and revving?
I suspect a faulty alternator since that is the last thing you changed.
12.5v is OK when off.. is your battery water level good?
I suspect a faulty alternator since that is the last thing you changed.
12.5v is OK when off.. is your battery water level good?
This is my best Ed impersonation.
“You need to check the grounds”
The negative battery cable attachment to the frame would be a great place to start.
“You need to check the grounds”
The negative battery cable attachment to the frame would be a great place to start.
Stumpalama
Forum Junkie
- Thread starter
- #4,426
Steve-O for the win.
And add a ground from the alt to the engine...
At idle the battery rests 14.4 .... no reving, and lights are on. 12.5 with truck off. Just went for a drive and the lights go on and off, they stay off when I’m on the gas even at low RPM. As soon as I’m coasting they pop on. Every once in a while they blink around and go off for a minute at a stoplight.... it is like it’s juuust close to staying off at idle. I’m wondering if the charge relay could be going, or if that would have a different symptom. Grounds seem fine. No squealing or anything from the belt.... I will note I did not change the belt on my trip when I changed the alternator, but the belt looks in good shape, and not making noise or anything..... dunno.
Also, the battery posts are nice and clean. I will double check the battery ground.
what brand alternator?
Also I just rechecked. 12.8 truck off ... 14.4 truck at idle and when I rev it or turn on ac there is no change so I’m assuming voltage regulator is fine. This beats the hell out of me.
ultima per my receipt. I was in a massive rush so I didn’t pay attention. They had one so I was overjoyed. I plan on getting OE back in. I still can’t figure this though. It’s not a short, because I can make it go away with throttle, but throttle doesn’t change voltage to battery much if any... it’s crazy.
Stumpalama
Forum Junkie
- Thread starter
- #4,432
Bad alt...
OK, This is weird!
My comments are based on the wiring of a 3rd gen 4R - I have the schematic. I don't think much has changed for the charge/brake circuits from 1st to 3rd. A schematic would confirm this if anyone has one.
The only thing in common between the charge light and brake light is the power source. The brake circuit is a simple power (+) to bulb and a with to ground (-) for the brake fluid reservoir and one for the parking brake. Either switch can turn on the bulb. Battery/Alternator voltage has no impact on this circuit other than a dim bulb if the voltage is low or a burned out bulb if the voltage is too high.
The charge bulb has the same power (+) source and the charge controller (inside the alternator) switches the circuit to ground (-) to turn on the bulb.
If both bulbs light continuously and simultaneously (never one on by itself) then I would guess that the wires that go to the regulator and brake switches are touching somewhere. When on thing (regulator, brake reservoir or parking brake) gets switched on, both bulbs have a ground path.
Question: When you put on the parking brake does the charge light also light? If no, then the previous guess is incorrect.
The other question is, why do the lights come on? Since it is idle related, I would suspect the alternator's regulator, and the brake light is just going along for the ride.
Is the alternator the correct one for the vehicle? Is the pulley the right size?
You might want to invest in a cigarette lighter plug volt meter so you can keep an eye on the voltage while driving Something like this: Amazon product ASIN B00UCEAKYU
Comments? Thoughts? Obscene remarks or rude gestures??????
My comments are based on the wiring of a 3rd gen 4R - I have the schematic. I don't think much has changed for the charge/brake circuits from 1st to 3rd. A schematic would confirm this if anyone has one.
The only thing in common between the charge light and brake light is the power source. The brake circuit is a simple power (+) to bulb and a with to ground (-) for the brake fluid reservoir and one for the parking brake. Either switch can turn on the bulb. Battery/Alternator voltage has no impact on this circuit other than a dim bulb if the voltage is low or a burned out bulb if the voltage is too high.
The charge bulb has the same power (+) source and the charge controller (inside the alternator) switches the circuit to ground (-) to turn on the bulb.
If both bulbs light continuously and simultaneously (never one on by itself) then I would guess that the wires that go to the regulator and brake switches are touching somewhere. When on thing (regulator, brake reservoir or parking brake) gets switched on, both bulbs have a ground path.
Question: When you put on the parking brake does the charge light also light? If no, then the previous guess is incorrect.
The other question is, why do the lights come on? Since it is idle related, I would suspect the alternator's regulator, and the brake light is just going along for the ride.
Is the alternator the correct one for the vehicle? Is the pulley the right size?
You might want to invest in a cigarette lighter plug volt meter so you can keep an eye on the voltage while driving Something like this: Amazon product ASIN B00UCEAKYU
Comments? Thoughts? Obscene remarks or rude gestures??????
The plot thickens.... I just went out again. I pulled the charge fuse (7.5 amp) .... lights go off, but voltage at battery is still 14.4 .... What’s going here? What does the charge fuse do.... how is the alternator sending extra amperage to battery terminals if the charge fuse is pulled?
Stumpalama
Forum Junkie
- Thread starter
- #4,435
How does the size of the original alt pulley compare to the replacement?
@TimberTrek Check out post 4415 above (p221). Access for oil changes is something else to consider for your skids, Stump went with RCI.
Thanks Ed!
No. When the charge/brake lights are off and I just pull the brake, only the brake light comes on...
I suspect the regulator as well but I don’t really know why. Only that regulators can cause issues with these lights but the readings don’t add up. I though maybe it was overcharging, but the throttle-to-lights-off wouldn’t back that up I don’t think......
Never happened except when I first had the issue...then not until today. I do believe it’s the regulator. Reading at fuse is 13.5 volt on 1 side and under 1 volt on the other. I think the regulator is sending the wrong information to the fuse block. Per FSM that should read 12v at fuse block (I think)
I’ll check tomorrow
