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Alternator Light Flickering

11K views 38 replies 5 participants last post by  ledzilla 
#1 ·
A while back the alternator light started flickering in my 78 LTD, and began to do it increasingly. Checked the charge voltage at idle across the battery while the engine was running, and it can back under 12V (it may have been as low as 11.4V by time I obtained parts). Replaced the alternator and voltage regulator, problem went away. Well, it started doing it again. Checked the charge voltage at idle once again, but the multimeter is reporting a voltage of 14.3V. The higher the RPMs, the less the light illuminates, if at all. I haven't had a second person yet to help check with the RPMs kicked up enough to turn the light off, so I don't know how that will differ. Any thoughts?
 
#3 ·
The battery is new, and the old alternator was replaced within a week after the issue started. And that was several months ago. Could the battery be damaged that quickly and take several months to manifest evidence of the damage?
 
#5 ·
Try gently wiggling the wires particularly the thicker ones on both the alternator and voltage regulator and see if the charge light goes off. These multi-strand copper wires can get brittle with age particularly if:

a) they run near hot engine parts like the exhaust headers (do they?); or
b) something has been wrong with the charging system and too high a current has been running in the wires, or
c) someone has been messing with the wiring (bending it too tightly or creating short somewhere)

... and individual strands break increasing the wire's resistance and preventing the alternator delivering a full charge to the battery. If so wriggling the wire will sometimes make the broken strands connect briefly and the charge light to extinguish. Check the full length of these wires between the alternator and the regulator and the battery to see if any of these wires (particularly the thicker multi-strand wires) are discoloured by heat exposure or feel stiff.

Also check the wires at the alternator plug are properly connected and there is no evidence of fraying or damage at the connectors.

If it has one (I suspect it has) also very carefully check the fusible link wire at the battery as this is usually part of the charge circuit and again they tend to break down with age (or if there has been a short somewhere) and prevent the charging circuit working correctly; if the fusible link wire looks even slightly swollen or discoloured replace it. Similarly check the connections at each end of the fusible link. You can also try the wiggle test on the fusible link but generally it won't work as the insulation plastic generally partially melts and reforms around the wires in the fusible link.
 
#7 ·
Ok, so the light stopped flickering once I got to work and put the car in park. Still had the multimeter in the car. Checked the voltage: 14.38V. I haven't had a chance to see if wiggling the wiring on the voltage regulator helps. But there's no plug connected to the alternator. There are three wires connected to posts on the back, one of which is secured in place with a nut. Not really willing to wiggle them while the engine is running, given their location.
 
#9 ·
Ok, so now it's not flickering so much, if at all, and I haven't had a chance to do anything about it (too cold outside). It would flicker a lot when driving down low speed residentials, but it only seems to be flickering when idling out of gear. I dunno. I need to pay better attention maybe.

Because it seems to flicker plenty when first started. But it's hardly flickering at all when driving down the street or when stopped at red lights.

Getting a little confused now, since it would previously only stop/reduce flickering when travelling at least 45mph.
 
#10 ·
If you had a car with a amp gauge fitted , you would see the alternator charging at a higher rate due to the drain / draw on battery after start up .This then USUALLY drops as engine revs increased on driving unless a fault in charging circuit or battery ( or both ).
 
#12 ·
Loading on alternator and battery varies tremendously on driving , time of day and year and conditions . Stop start short journeys , night driving with h/lights on , heater and air con , wipers , rear demister etc . especially on older cars .That's why I like cars with amp , oil gauges to name a few , instead of warning lights .You can see what's happening with your vehicle .Also ensuring alternator correct output ratings
 
#13 ·
Ok, so I took a shot and replaced the voltage regulator since it was still under warranty. No more alternator light. But for only a few minutes. The light came back on. While the light was off, the battery read 12.35 volts. When it came back on, 14.6 volts.

So I'm left with the conclusion that either I have been getting crappy voltage regulators, or something is causing them to fail.
 
#15 ·
Honestly, no. I kept forgetting. But after it only taking a couple minutes for the light to go from off to on, with no more flickering, I'm not sure it'll help now. I'll give it a try though tomorrow when I'll have daylight to work with.
 
#16 ·
Ok, I'm starting to wonder about something now. I replaced all of the bulbs in the instrument cluster with LEDs, including all of the warning indicators. Is it possible that the low resistance on the LED bulb can cause it to give false error indication? Maybe I should swap it out with a standard bulb just to be sure. I still have all of the bulbs I removed.
 
#18 ·
Ok, tried the light, it still lit up. Went and checked the wires on the regulator, stayed on. Went and checked the wires on the alternator. As I was checking the two hard to reach wires, the close one fell off. Reconnected it as securely as I could, no more light. Double checked the voltage, and it was 14.4 volts. I guess the literature I saw yesterday about how it should be between 14 and 15 volts is correct. Didn't need to swap out the regulator after all.

But, I'm going to need to keep an eye on that connector. It didn't feel very secure on the terminal. If this all happens again, though, at least I have a first place to check for now.

There are two of those connectors that are meant to just be slid onto a threaded terminal. I'm thinking maybe I should replace those with ring terminals so they can be secured with a nut. Just not sure how that would work with the connector cover
 
#21 ·
Any idea on the thread size for the terminals? I don't think I kept the nuts when I got the replacement alternator (I think I put them on the old one before returning it for the core), and I'd prefer to not need to remove the alternator and bring it to the hardware store.
 
#23 ·
If that's for the battery terminal, I'm not certain. I think the trouble terminal is the stator terminal, which is smaller. And I'm guessing as to whether it's the stator or field terminal, since the color wires in the car don't match the wiring diagrams.

The diagrams all show black/orange, white/black, and orange/lt blue. My car has white, black, and red. The only one I know for certain is the red wire connects to the battery terminal on the alternator.
 
#24 ·
Oh, crud. Never mind the wiring colors. I kept looking at the wiring for a side-terminal type. The diagram for the rear-terminal type shows the colors I have. And maybe it is the battery terminal. Ugh, I have to go investigate it to make sure.
 
#26 ·
Yeah, the orangish-red colored wire seems to be the thickest. The loose connector is a black wire, but there are two wires connected to the connector, both black. As for the alternator, I don't know what brand, but I bought it from NAPA.
 
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