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Alternator/charging light on 1984 Volvo 240 glowing VERY faintly

F

Frank_Rizzo

New member
Joined
Jul 24, 2018
I first noticed this this evening, as I was driving at dusk. The alternator warning light does not glow at all, however, on startup, like it should (and had been doing consistently until today).

This did happen once about a year ago and it indicated a failing alternator diode. I was wondering if you had any further thoughts on the matter. Thank you.
 
Perhaps the charging warning light itself might be defective as well?

Since it doesn't light up at all (while the oil pressure light does) when I put the key into "on."
 
Roll fuse 13.

No, nevermind, you said the lamp test doesn't work, so the alternator D+ wire isn't seeing a path to ground. Check the ground wire at the alternator before attending to the brush pack.
 
Thanks for all your responses. After checking the wires and ground, the indicator light itself wasn't defective, the alternator itself was shot. I'm getting a new one. Thanks once again.
 
ZVOLV said:
Post back with the results.
Click to expand...
I did a few posts ago.

Not the belt, not the exciter wire, not the ground, but it was the alternator (some third world piece of crap) itself. I got a "free" replacement from O'Reilly's but I'm planning on getting a Bosch alternator 70amp in the next few months as backup for the next failure.
 
Mine had the same issue. It can occur when the diode pack for the D+ and B+ have different resistances. Thus a voltage drop occurs between B+ and D+ and you see the light glow. I drove mine like that for quite a while before I replaced with a denso 100a. If you're getting proper DC at the battery terminals and no AC, it's doing its job. It's just the self-diagnostic portion of the alternator that's faulty. Over time though, the diode resistance causes heat and might eventually kill it.

The diagnostic D+ terminal is supposed to always show proper charging voltage and it gets compared to what your battery is receiving. When they differ (usually because the battery is receiving less), the light glows. But, the light will also glow if the battery is receiving proper voltage but the D+ is getting less.
 
I also have encountered a genuine Volvo bosch alternator that had different voltages on the D+ compared to B+ terminals. The voltage was lower output on D+ so the light was on very dim on the dash but the charging voltage was actually ok. I have to get a diode pack for the D+ output one of these days.
 
dl242gt said:
I also have encountered a genuine Volvo bosch alternator that had different voltages on the D+ compared to B+ terminals. The voltage was lower output on D+ so the light was on very dim on the dash but the charging voltage was actually ok. I have to get a diode pack for the D+ output one of these days.
Click to expand...

I just threw a philski denso in because I got tired of looking at the dim light.
 
I run the Denso too for many years on my two cars in the sig. That story was about the brand new Volvo alternator I bought at the swap meet at Volvo headquarters. Probably about 1995. It is one of the reasons I changed over to the denso ones.
 
I'll add that you should check that gnarly grounding strap that runs under the motor for the alt... they corrode and in my case, before my car lit itself on fire, I had noticed odd things happening with dash lights. Only the batt light though, I would suggest just looking at the brushes. But check it all while you're there. Car fires are no fun.
 
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