Does anybody know why my voltage light keeps coming on? The needle shoots way past the 18 mark also. It doesnt do it all the time. My mechanic checked it out with his tester and seems to be fine. Of course the light wouldnt come on when i went to his house. But we had the lights on, the A/C, the stereo, and the car running of course, and the darned light wouldnt come on for him. The light is on again today. The car starts fine, and the voltage light is very dim. The cables are on tight. Any help would be appreciated. Thank in advance.... Lorin
87 gt

Did you have the alternator tested? I believe stores can test it in the car.

J.

I thought that when he was testing the battery with his voltage reader that it was also testing the altenator? Sorry i dont know much about cars but the basics. But I thought if the charge was correct then the altenator is doing its job?

Do the lights get brighter when the voltage spikes up? If so your voltage spikes are real. Only thing that could cause that is a bad regulator/alternator. (regulator is inside the alternater) It can be replaced by taking the alternator apart but many just replace the alternator and have it for sure.

While the car is running the alternator should be putting out about 14.7 volts to re-charge the battery. If the votage is below 14 - then the alternator isn't re-charging the battery how it should. If its above 15 then the alternator is overcharging the battery. The first question I have is "is the gauge actually reading an overcharge" If the lights get brigher during that period then yes it is.

The light coming on would indicate that the alternator isnt charging the battery. The oppisite of the first condition. Since these both come and go that really points to a bad alternator.

[This message has been edited by phonedawgz (edited 07-09-2010).]

No the lights Do Not get brighter when the needle spikes, and the volt light comes on.

quote Originally posted by signtist2004: ... my voltage light keeps coming on? The needle shoots way past the 18 mark also. It doesnt do it all the time.

99% probability that the problem is a bad voltage regulator, most likely failing when it gets hot. Time for a replacement alternator. Overcharging may have already damaged the battery, too, if you've driven very long that way. Unlike the earlier SI-series alternators, the CS alternators (used in the '88 Fieros, not sure about '87s) do not use use the alternator lamp circuit to provide field current, but only to signal either low or too-high system voltage.

quote Originally posted by Marvin McInnis: Unlike the earlier SI-series alternators, the CS alternators (used in the '88 Fieros, not sure about '87s) do not use use the alternator lamp circuit to provide field current, but only to signal either low or too-high system voltage.

I did not know that - high voltage part - cool! Will wonders never cease

[This message has been edited by phonedawgz (edited 07-09-2010).]

I didn't either, until I had it happen to me in my Formula several years ago. System voltage (~18 volts) was limited only by the battery's capacity to sink the excess current being produced by the alternator, and the warning lamp was on.

[This message has been edited by Marvin McInnis (edited 07-09-2010).]

Any Fiero uses CS alt is "I" setup. (See cave, CS alt.) 88 V6, 87-88 L4, and some 86 L4 after half year change I'm told.
Both I and L line can be used for "excitement" Field current. I line is backup for L line and light bulb in dash.

Usually a Bad reg in alt.
Check for bad wires or connector to alt. If Sense pin, wire or splice to Sense, flips out even for a sec, Regulator doesn't work right. Sense is Big wire to side plug and splice to main alt output.

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does anyone have a photo of where the altenator is? along with the wires that go to it so i can see if anything is loose or corroded?

Dont rush off and buy a new alternator. The problem is most likely just a lose or dirty connector on the alternator. If you get under the car and look up at the alternator you will see a connector with only one wire - light gage wire- pluged into the alternator. Make sure it is on good and clean. If that connector gets lose your volts will go to like 18. Some folks change the alt thinking it was bad, when in fact it was simply the act of of unpluging that wire and reconnecting to the new alt that fixed the problem. The didn't realize it but they cleaned the connector a lil the process.

Sadly more often than not, Fiero owners run off and waste money on things they didn't need such as ignition coils, moduls, alternators and even starters when the problem is connector related. These cars are old and connectors tend to corrode and become iffy. We've all read about people here buying a new ign coil or other ign item evey 6 to 8 months or whatever and not realizing it really a connector related problem. If you -everyone- start to have an intermitant problem replace all of related connectors: Sensor, Ignition, etc.

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quote Originally posted by Marvin McInnis: Unlike the earlier SI-series alternators, the CS alternators (used in the '88 Fieros, not sure about '87s) do not use use the alternator lamp circuit to provide field current, but only to signal either low or too-high system voltage.

That's interesting. Because my Fiero has a CS alternator, and recently the Volts light burned out. I didn't realize it until the battery was almost dead, because the alternator wasn't charging. I plugged in a new bulb, and everything was fine.

I verified this with a Voltmeter. With the bad bulb, it read about 10V with the engine running. After replacing the bulb, it went back to about 14V with the engine running.

quote Originally posted by Blacktree: That's interesting. Because my Fiero has a CS alternator, and recently the Volts light burned out. I didn't realize it until the battery was almost dead, because the alternator wasn't charging. I plugged in a new bulb, and everything was fine.

That is interesting. Is your Fiero an '88, or is it an earlier model that has been converted to use the CS alternator? Below is an excerpt from the '88 GM/Helm FSM, showing the CS alternator wiring. Note that the "voltage sense" input ('S' terminal) is spliced directly to the alternator output, and the "field" input ('F' terminal) is fed directly from the fuse panel. (This assumes, of course, the the cars actually left the factory wired according to the schematic.)



Looking at the schematic does suggest another possible cause for an overvoltage condition. If splice S501 is bad (e.g. corroded or frayed) or, as Francis T has suggested, there is a poor connection at the 'S' terminal, it could cause loss of voltage sense to the alternator and subsequent high voltage and overcharging.

[This message has been edited by Marvin McInnis (edited 07-10-2010).]

Yeah, it's an earlier wiring harness that was converted. The recommended procedure for making the conversion involves leaving the brown/white wire disconnected, for some reason.

That said, my engine has an alternator for an '88 V6. If I can connect that brown/white wire to an ignition power source and avoid the burned-out bulb issue, that would be great.

[This message has been edited by Blacktree (edited 07-10-2010).]