I drove a lovely little girl in a Home Coming parade last Tuesday evening. Car was running great. Still had oil in the engine and I'm 50 miles from home, at night, on the Natchez Trace Parkway. Somewhere, before I got home with the engine running well, the alternator light failed. If the light fails while the engine is running you have no way of knowing. About a mile from home the headlights dimmed...nearly went out. I got to my neighborhood and the car began to buck and snort, obviously the battery was about to give up. I turned off the lights and was able to drive into my garage.

Next day I installed a new alternator, started the engine and no juice. Everything is wired correctly, must be a bad alternator. Exchange it and installed the new new alternator; no juice. By now  I'm really frustrated. I had that alternator in and out 4 times checking the wiring ( what is the definition of insanity?)

I woke up this morning at 6:00, that's 4 a.m. California time, and knew what the problem had been all the time. The idiot light was out. I pulled the light and it was not burned out, but had been displaced in the socket enough that a good connection was not made. Now the idiot light is on; start the engine and I have 14.5 volts.

This may not apply to all alternators. My car has the 911 shroud ans run a Delco CS130 alternator. The mounting brackets are machined off to fit inside the 911 fan. 

I was really dreading the failure of the alternator because I suspected that the installation would be a bitch, but it wasn't. I could have been finished in an hour.

Beware of the Alternator light!



Original Post

“This may not apply to all alternators.”

Yes, it does apply to all alternators.  If the dash “charge” light is burned out or not making adequate contact to be functioning properly, the alternator (any alternator) will not charge.

Technically, the dash light wire (labeled “D+” on top of the alternator) provides an initial electrical path for the alternator field coil to begin charging once the alternator starts spinning.  If the light is defective, no field charge.  The alternator internal magnets are not adequate to maintain charge on their own.  They need the field winding operating to start or maintain the charging sequence.

Glad you found the culprit.  Most people wouldn’t look there, especially if the light is out!

Those little 4W bulbs in those little brass sleeves are notorious for corroding over time and failing to work (the solder button on the bottom of the bulbs, and where the sleeve inserts into the gauge, too).  If you swap an alternator and still no charge, first place to look is the dash bulb.

Last edited by Gordon Nichols

I used a 50-ohm 10-watt power resistor in parallel with a 12V rated red LED lamp assembly to replace the alternator lamp when I upgraded the dash lights to LED. It functions much like the original lamp. A word of caution... the resistor gets rather warm when the key is on and the engine is not running, or if the alternator is not making power. Position it so it hangs in free air, not tied to a harness. https://www.ebay.com/itm/PLB12...p2057872.m2749.l2649

Last edited by Eric (McGruff)

Since I have the Speedhut gauges, they have all LED lights inside them. I chose to use the LED meant for something else for my alternator light. It did NOT have the resistor wired with it to give enough resistance(load to the alternator) to work. So, I used a relay to trigger it with a 500 ohm coil. Now it works properly!

If you use a relay, it won't matter if the light ever burns out.

Stan Galat posted:

(as long as the relay coil doesn't burn out)

Yes, but that happens less often than a bulb burning out.

I've never actually had an idiot light burn out in ANYTHING. This problem came out of a loose connection between the light and holder.  While being intimately involved with replacing the alternator; every time I turned on the ignition an idiot light (wonder they call them that) came on, but it was the oil light! I wasn't paying attention to the color; just the light.

I've been repairing mechanical things all my life; well for 55 years anyway. If it's on a car, motorcycle or personal airplane, I've touched it. I'd bet that average self taught, but highly skilled, mechanic is unaware that the idiot light out would not allow the alternator to work. I sure wish I had known that.

This thread has only had 118 views. Our other friends really need to know about this.

Geez, I hate stuff like this.  I had a turn signal bulb go out on my truck.  I replaced it with a new bulb.  Still no turn signal.  Truck has one of the all in one boxes, turn, flasher etc., 85 bucks.  Replaced the box, still no turn signal.  Continuity check, new bulb was bad.  85 buck lesson, new doesn't mean always works.  People wonder why I can be grouchy.

If I had an alternator that wasn't charging, I would replace it.  If the new one didn't charge, after some harsh language, I'd probably try to rewire the entire circuit.  I'm not sure I'd figure it out without this thread.  You all are aces.

I'm OCD about a lot of stuff, including all my rides being roadworthy.  This one is going in my fixes log.  

When I had a 2000 F150 it had a problem with failing coil packs.  It had 8 ignition coils, one on top of each spark plug and they were subjected to cylinder head heat all the time, so they failed, randomly.

Trying to get ahead of it just before we were scheduled to make our pilgrimage to South Carolina from Rhode Island, I bit the bullet and replaced ALL of them, to the tune of about $650.  It started and ran like a top.  

We got packed (we would fill the back of the truck with "stuff" from one house to the other) and took off.  Just about the time we got to I-95 in Rhode Island, the engine started to skip constantly.  Nothing affected the skip - it was there all the time.   "Screw it!"  I thought, and we kept going, expecting to fix it when we got there, 1,000 miles later.

When we arrived, I went to the Ford dealer and the service tech told me I had a bad coil pack.  "Impossible!", I said.  "They're all brand new!"

He told me that they get roughly 10% - 15% of their electronic parts that are DOA when they install them.  They (we) just have to deal with it.

In light of this (you see what I did there?) and of all other recent issues-- this country may want to rethink it's dependence on China as an integral link in it's supply chain (I'm looking at you, Apple).

The quality goes in before the name goes on, except on Tuesdays, when Ralph has to pick up his kids at daycare and leaves early because that’s when his ex gets her hair done and the local won’t let us bring in a temp to cover without paying full benies and no one’s gonna approve that.


Stan Galat posted:

In light of this (you see what I did there?) and of all other recent issues-- this country may want to rethink it's dependence on China as an integral link in it's supply chain (I'm looking at you, Apple).

I have been saying this for years.  I don't mind paying more for my stuff; I would probably just have less of it.   

I do think that is the right point of view but in a free market unless you lock out those that want to go where stuff is cheaper by cheaper wages ie: third world from bringing there goods into your country then you have an uncontrollable market economy.  
The only controlled and planned economy did not work hence the wall fell and those living in East G, found out they were 40 years behind in one instance.

Gordon Nichols - F150 Coil Packs:  It's so annoying.  I find it hard to believe the maker  can't figure out a way to test them before shipping.  I know I'm shouting at the wind (I cleaned it up).

Stan Galat - Off shore manufacturing:  I remember one SEMA, I wondered into the expo across the way. it was scary to see how many parts are made in China and Asia in general.   

2004 F150 : I just replaced an aluminum fuel pump control module (Chi ni) that sits against the steel frame above the spare tire. They are prone to failing due to the aluminum - steel corrosion issue so for $30 I decided to replace it before it failed.  Simple 1/2 hour job until I found the spare was frozen on the winch cable and one of the two module bolts snapped off in the frame. So 2 1/2  hours later I had it switched out, put al the tools away and started the truck …. it will barely run. Put they old one back in, snapped the retainer clip on the harness end so that required a zip tie to hold the plug harness into the module but it ran.  A trip NAPA to part with $30 for a module harness that I have to slice into the factory harness tomorrow . So where am I with this ?  I still have the old fuel pump module in place,  ( I did clean up the chalked aluminum base and glued a rubber pad to it. I have to do the harness then get a refund from the eBeg  seller.

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