battery light (idiot light) started staying on ??

[royzell]

Hey all,

'88 7.3 automatic, fairly recent batteries and rebuilt alternator (from a parts truck of mine).
The volt gauge shows right in the middle, but today my battery light came on and stays on. The 1st time it went away when I revved it, but now stays on regardless.

Any ideas as to the problem ? electrical gremlins are a weak point for me.

 

[DragRag]

Likely the alternator is taking a dump, and fast. That happened to me, and I thought I could skate by for a couple days. Got stranded because my headlights over took what the charging system was putting out, which wasn't much. Mine started flickering at higher revs, then eventually stayed on. Change it before you get stuck somewhere.

 

[royzell]

'that could be the case. I forgot to mention that when I start the truck, the voltage gauge stays to the left (negative) until the revs are up.

I have another spare I can swap tomorrow.

 

[DragRag]

Getter done, as Larry would say.

 

[WrickM]

my 1987 6.0 has the battery light flickering all the time and has for months. The voltmeter seems to indicate the alternator is operating well enough but that stinking like just flickers endlessly. I've thought about just pulling the bulb.

 

[sassyrel]

nope, like the other one--alt dying--just real slow---

 

[CDX825]

Swap in a 3G and be done with it!

http://www.oldengine.org/unfaq/3ag/3ag.htm
http://www.fordfuelinjection.com/public/alternator/3G-ALT_wiring.gif

 

[argve]

how is the vacuum pump working. Do you get an hard brake pedal every now and again. The vacuum sensor will trigger the brake light on these trucks. The sensor is located on the passengers side fender well. So I would check the vacuum on the truck before going off and replacing the alt, you should have 16 inches of vacuum at a min.

 

[Agnem]

Not sure what the 87-91 trucks look like, but if they are doing it the same as they did on the 94', then the alternator has an on-board regulator, and has only 2 wires. The heavy output wire, and a wire that is fed with Key-On power (green with a red stripe IIRC). That Key-On power comes through your instrument cluster, and is fed through the battery indicator light, in parrallel with a 50 ohm resistor. I guess the way it works somehow, is that the voltage passing through is not enough to lite the bulb, but supplies power to the regulator. If there is a failure in the regulator or alternator, this signal somehow is grounded, and the bulb will lite. Not sure what happens if the bulb burns out... maybe that is the function of the resistor.

As an aside, check out this intriguing rebuilders trade article on the new 4G alternators.

 

[WrickM]

Mel,
That makessense. when i was looking for a new tach i got a gauge cluster from my local u-pullit and the battery light on that cluster had a resistor built right into it. However the light on my truck's cluster did not. In fact there was another resistor on the circuit board that my truck also did not have. Who knows if my truck has the original bulb in it or not. they guy who had it before me kinda half assed some stuff.

 

[Dsl_Dog_Treat]

Voltage regulator died???

 

[jhnlennon]

I second trying the voltage regulator, my light was flickering in my 87 when the voltage regulator was bad. They are cheap and should be replaced anyway if you are replacing your alternator. This is for the externally regulated alternators.

 

[Alex S]

I had charging problems at times it wasn't charging and then at times it was over charging (like 18V) I did some test and put a new ground wire between the body and the regulator and all was fine

 

[royzell]

'swapped in a spare alternator today. The battery light went out, but the volt gauge on the dash still stays to the left until the truck has run for a while.

I need to buy a test gauge, and look at the 130 amp conversion .
I have a spare voltage regulator, I'll try that on the weekend. i was wondering about it also. Brakes and vacumn appear fine.

 

[sassyrel]

'swapped in a spare alternator today. The battery light went out, but the volt gauge on the dash still stays to the left until the truck has run for a while.

I need to buy a test gauge, and look at the 130 amp conversion .
I have a spare voltage regulator, I'll try that on the weekend. i was wondering about it also. Brakes and vacumn appear fine.

it will stay to the left--gp's cycling--