84 Fiero Lights Causing Low Voltage (Page 1/3)
maxalator MAR 29, 09:55 PM
I've been having this really bad issue where the voltage drops whenever the Lights or blinkers are turned on causing the voltage to drop all the way down and the car to start running poor. I've replaced the alternator and checked the fuses but can't seem to find the issue. Its not caused when pressing on the brakes only when the lights are turned on or when the blinkers/hazards is hit. Any help would be very much appreciated as my brother is needing the car here soon.
olejoedad MAR 29, 10:43 PM
Start checking power connectors and grounds.
Make sure all the contact points are clean.
WalkerTexan MAR 29, 10:48 PM
Does the voltage drop when you turn on the lights and the engine isn't running? If so, then that rules out the regulation of the alternator and only leaves either a weak battery or bad connections. If the engine starter is working OK then that rules out a weak battery and leaves highly resistive connections. I would inspect both battery cables, the positive connections to the block under the connectors near the battery and the grounds.
Patrick MAR 30, 12:37 AM

The most difficult ground to check, but one that often goes bad due to corrosion, is the ground for the rear wiring harness. It's located on the upper frame rail of the passenger side rear wheel well. The plastic wheel well liner needs to be removed, or at least loosened, to access this ground.
theogre MAR 30, 09:20 AM
See my Cave, Wire Service
But...
⚠️ Warning: 84 Wiring has many things are 84 only and many later diagrams are invalid for you.

Clean and grease ground ends bolted/screwed to block etc w/ permatex brake grease. (partly because likely need it for brake work too.)
Prevents water etc problems and won't wash out easy. Thin coat is all you need.

Hidden G400 only affects taillights and maybe Cruise parts. Don't bother w/ digging out the inner fender until you find real cause.

Besides checking/fixing grounds, battery cables, etc...
See my Cave, Alternator Sense
Iffy sense wiring will cause many problems.
Many bypass C500 for alt output too because this connector can burn up when have crap contact.

84 has 2 or more Fusible Links to the Starter Solenoid like have problems too. Check/clean all wires to the starter.
Do Not cut fuse links. If "bad" you must replace them properly. see cave.

Note: Low Volt from Alt often causes Battery problems.
Check battery volts and charge until see 12.6-13v and leave battery unconnected from anything overnight. Should stay about same volts next day.
Volt drops then battery is likely bad. Check at walmart AZ etc w/ computer battery tester but even dumb load tester likely fails too.

If you need battery cables, Only use ACDelco battery cables. Aftermarket cables w/ Lead battery ends won't last long w/ side term batteries.
take off bolts and cover on battery ends, Coat them and battery "posts" w/ brake grease, then install.

------------------
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

[This message has been edited by theogre (edited 03-30-2022).]

maxalator MAR 30, 04:06 PM
I'd like to note that the problem I'm having is only when the car is running and since I have an 84 I can see on the voltage gauge that when I press the blinkers it won't change nearly at all and then it suddenly drops and the car starts dying. This problem also occurs when I turn on the headlights whether they are already up or not. The battery cables aren't the greatest but they aren't rotting or have exposed wire. I hadn't had any of these issues until just recently when I started using it more after winter ended. Is there any specific area where the headlights and the blinkers coincide?
WalkerTexan MAR 30, 04:37 PM
The headlights and the ECM both have fusible links that are connected at the junction block near the battery, under the large connectors. If the connections there are corroded you could have problems like this.

From your clarification I assume the lights and turn signals aren't dimming or turning off but rather only the engine is dying so you may have a bad fusible link F to the ECM (or whatever link letter is used on the 84) as well or in addition.

The fuse block has the source for the gauges fuse and ECM fuse tied together so a drop to the ECM would also show a drop on the voltmeter. It might make sense to check for corrosion in the fuse block, too. I suspect the junction block first since it is subject to weather more than the fuse block.
maxalator MAR 30, 04:39 PM
I made a video of almost exactly whats happening except its much worse when actually driving.
WalkerTexan MAR 30, 04:42 PM
Also, the brake light fuse is hot at all times whereas the ECM and voltmeter aren't so that current path is completely different. That would help explain why the brake lights don't cause the issue.
olejoedad MAR 30, 06:08 PM
The 84 doesn't use a Battery Junction Terminal.

Battery power is pulled off of the starter lug.