Charging Warning Dash Light and Battery Not Charging (Page 1/2)
PaulJK AUG 10, 06:16 AM
Maybe someone can help me understand this. i guess it applies to any engine, stock or swapped.

There is a warning light on the fiero dash that comes ON when the alternator stops charging. If this light bulb is burnt out, the alternator will NOT charge and the battery goes dead. If the wiring in this circuit is broken, the alternator doesn't charge and the battery goes dead.

Is this a direct connection to the alternator or does it go to the ECM and the ECM tells the alternator to stop charging ?

Is there a "work-around" to hardwire the alternator into thinking this light is always working, such as grounding the "control" wire ?

I'm asking for a friend and myself. On several fieros I've had, including my 3800SC, I've had problems with this.

Maybe someone has a wiring diagram (?)

Thank you.

[This message has been edited by PaulJK (edited 08-10-2014).]

FieroJimmy AUG 10, 07:23 AM
This only applies to the non-ecm controlled CS series alternators, as I recall. The alternator is expecting to see a small amount of resistance back to switched B+ on one of the control circuits (I don't recall which at the moment). You can wire a resistor between an ignition switched source to bypass the charging light. Or there are SI to CS adapter harness with it built in. If you look into CS conversions for vehices without factory charge lights you can read all about it. The forums at ColoradoK5 have some good info.

[This message has been edited by FieroJimmy (edited 08-10-2014).]

olejoedad AUG 10, 09:40 AM
The alternator plug must have 12v constant (battery) on terminal A (red). This is supplied from the battery junction terminal below the c500.
Plug terminal B (brown) is 12v ignition and is supplied from that GAGE fuse power routed thru the charge indicator light.
Both voltages must be present for the alternator to charge.
Because 12v is on both sides of the bulb when the alternator is charging, the bulb does not light. If the alternator quits charging, the bulb lights due to power flowing from the GAGE fuse to the alternator.
theogre AUG 10, 10:51 AM
If SI then need the light circuit to turn on the alt.
If CS type... See my Cave, CS Alternator

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Dr. Ian Malcolm: Yeah, but your scientists were so preoccupied with whether or not they could, they didn't stop to think if they should.
(Jurassic Park)

The Ogre's Fiero Cave (It's also at the top and bottom of every forum page...)

sardonyx247 AUG 11, 06:04 AM
You just need to wire in a 50ohm resitor in parallel to the light so in case it goes out the alt still charges.

If the light comes on when the engine is running, either the alternator is failing/has failed or the battery voltage is dropping. Try revving the engine and:
◦If the lamp gets brighter, suspect a bad battery
◦If the lamp gets dimmer, suspect a bad alternator

This all being without a slipping belt.


And if you want an OVERLOAD of info on alts go here http://www.pirate4x4.com/te...avista/Wiring/Part2/


Edit to add: Orge you may want to read the link, it explains the missing info on your CS page


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"DRIVE IT LIKE A FIERO"
'84 Fiero, engine to be determined '87 Duke (Sold)
'87 Quad 4 H.O.
'87Blue GT 3.4L Swap Completed!!!!!!!! Boosted!!!!!!!
^^^^ Now in the Construction Zone^^^^
Las Vegas Fiero Club Parts/Sales/Service/Club
Fiero Road Club Of Northern Nevada

[This message has been edited by sardonyx247 (edited 08-11-2014).]

chuck3464 AUG 11, 08:02 PM
i have a 87 fiero 2.8 auto , someone tied into the red wire next to the battery and ran it up to the key switch and if i unhook it the light on the alt gage will come on , not had time to trouble shoot it yet , working on other things , hope this helps
phonedawgz AUG 12, 01:58 AM
On the 3800 - IF THE PCM IS WIRED TO CONTROL THE ALTERNATOR

The PCM controls the alternator.

The PCM also controls the CHARGE light

The PCM won't get upset if the CHARGE light isn't hooked up. It will still run the alternator and charge the battery
Fiero.1984 AUG 21, 08:50 PM
This is a common thing. I have another car MGB that does the exact same thing. The light adds a small resistor to the circuit and cause a current to flow to the alternator which creates a magnetic field for the alternator. Some alternator are self actuating and this resistance is not needed. Sometimes an alternator will have enough residual magnetic field that it will work without the light but the magnetic field can fade with time. The easiest way to fix it is to replace the light bulb. Putting a resistor in parallel will also fix it but it seems to be extra work.
FieroCat SEP 11, 10:19 AM
I don't quite understand how the alternator doesn't charge without the battery light on the dash. I removed my aux gauge pod a while back and have not had any real charging issues. Mine is a 1986 though?

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My Fiero: 1986 Pontiac Fiero GT, V6, 4-speed manual

Lou6t4gto SEP 11, 01:48 PM
On my conversion, the light is off, it charge., the light comes On, it still charges. the light is always going on and off. so I am of no help here.