1991 740 Alternator is not charging the battery

Wsivik+740 · Post by **Wsivik+740** » 15 Jan 2014, 23:32

The problem started a few weeks ago when I was on my lunch break at work. I was driving back to work when I noticed my dash lights and electronic accessories were glitching out and all the lights were dim. About 10 min later the car acted like it was going to die like it was out of fuel. I managed to make it back to work in the parking lot and I let it idle for about 10 min before turning it off.
Once I turned it off I tried starting it again, but the battery was completely dead. After work I asked a co-worker for a jump start. When I got the jump start, it started fine and ran great for about 10 minutes then all my electronic accessories starting to get dim and glitch out, then my car completely died.
My first thought was that it was the battery, since the one I had was pretty old. When I put the new battery in my car ran fine for about a day and half and the same problem happened. So then I figured it had to the alternator. I took my alternator out and took it to an auto parts store to have them test it. The store tested it three times and said it worked great. After reinstalling my original alternator I cleaned all the electric cable leads and made sure they had a good connection. Still about a day and a half later my car died with a fresh charged battery.
A few days ago I found a used alternator and installed it. I drove my car over to the auto parts store and had them run a diagnostics test. Their device said my alternator had a faulty alternator regulator, so I decided to just buy a brand new alternator. I installed it there at the store and had them check it again. The tester said that the regulator was bad in it. I personally find it hard to believe that I have 3 bad regulators when the original tested fine, and I threw a brand new alternator in it.
This is where I am stuck. I did notice that the alternator power cable comes from the starter. Could it be possible that I have a faulty starter that is not allowing the power to flow from my alternator to my battery? Any suggestions or comments will be much appreciated thanks!

Post by **jimmy57** » 16 Jan 2014, 06:20

When you turn on ignition but do not start engine does the battery lamp light?
The alternator will not charge until you rev engine over 3000 rpm if the light circuit isn't working. The current through the bulb goes through the brushes and finally to ground in the alternator. This current effectively "primes" the alternator to begin charging. Without that current the alternator has to spin to a very high rpm before it outputs any current needed to magnetize and then produce current.

Wsivik+740 · Post by **Wsivik+740** » 16 Jan 2014, 17:37

Today I pulled my starter and took it to an auto shop to have them bench test it. The starter tested fine. After I reinstalled my starter I checked to see if my battery light came on and it did not come on. So if the light does not come on then what does that mean?

Wsivik+740 · Post by **Wsivik+740** » 16 Jan 2014, 17:38

I am not all that great when it comes to electrical.

Post by **jimmy57** » 16 Jan 2014, 20:32

The small red white should plug onto a terminal on back on alt marked "D+ 61"

If it is and light is not on then unplug it and hold the terminal against some metal of engine while key is on and someone watches the instrument panel. If lights are lit with the wire grounded then the problem is with alt.
If the lights still are not on then the problem is likely the wire broken as it passes under front of engine or a bad connection of that same red white stripe wire where it plugs onto back of instrument panel.
That wire passes through an 8 wire gray rectangular connector next to brake booster on driver's side of firewall as I remember. Look to see that those wires there are plugged in securely.

Wsivik+740 · Post by **Wsivik+740** » 17 Jan 2014, 10:17

I have a plain small plain red wire coming off my alternator and tried to track it down in my dash yesterday but didn't have any luck I will try again today. Thanks for your input!!!

Wsivik+740 · Post by **Wsivik+740** » 23 Jan 2014, 18:04

After a very long headache I finally was able to fix the problem. A few months ago my speedometer went out in my instrument panel. I took the whole cluster apart and attempted to replace the fried resistors. I was unsuccessful, so I waited for a used one to show up which was yesterday and bingo problem solved. Somehow the connection in my old cluster was not passing through to make my charge light come on. I had I feeling that was it all along but just did not believe it. Anyways thanks for the advice and hope this will help people in the future.

Bullfrog · Post by **Bullfrog** » 11 Nov 2023, 10:46

I have this same issue. Speedometer and fuel gauge went out a few months ago now it won't charge. Did you replace the entire instrument panel?

Post by **volvolugnut** » 11 Nov 2023, 17:32

Bullfrog, note the last post in this thread was 9 years ago. Try starting a new thread.
volvolugnut