My new alternator is not charging the battery. It's a little complicated as I am a novice and might have caused the problem myself! Here it goes with the facts:
I have replaced my alternator (Autozone) 2 times, as I thought the 1st one was faulty. I have replaced the alternator bushings, Belts, Crankshaft Pulley Vibration Dampener, ground wire to block and an adjustment bracket bolt. I am confident all the wires to the new alternator are installed at the proper positions and securely tightened. I believe all was working correctly until I did a dumb thing. I was attempting to remove (Faulty light indicator bulb) from under the dash. The ignition switch was switched on to provide a little light behind the dash. I was using a small metal probe to do the task, and it seems that I touched something that caused sparks (short circuit). Well I removed the bulb, but quickly noticed that all my gauges in the instrument cluster are no longer working. The only gauge that even moves (erratically) is the speedometer. All the idiot lights are still working and the directional signals and horn still work properly. It still starts and operates, but only off the charged battery. While the engine is on, the alternator light is on and is dim and flickering unless I engage the overdrive button and it becomes bright. Note: My overdrive was and still does not work - Needs part that installs under the dash. Lastly, I pulled all the fuses out in the fuse box and under the hood, checked for continuity. All of the same fuses and respective copper holders were cleaned and reinstalled with no improvement. I know that perhaps some of this information may not be related to the main charging problem, but I just wanted to be thorough.

I'm very frustrated and feeling stupid about probing under the dash as explained above. I would be very grateful if anybody could help me diagnose and/or provide me with some suggestions. Thank you, Alex

 

there is a fuse integrated into the circuit board of your instrument cluster, this protects the lights, gauges etc.

Normally when this happens people simply solder on a short piece of wire and bridge the fuse as its not replaceable.


As for the alternator not charging, is it actually not charging or is it simply displaying weird on the cluster. If you have a multi-meter, check the battery voltage with the engine off and with the engine on, does the voltage go up or down?

Oddly enough, If you have some cluster issues, even a bad charging circuit light bulb, your alternator may not charge the battery. It all has to do with the "Exciter Circuit" as an alternator needs power applied to it in order to charge.

http://www.volvowiringdiagrams.com/v...240%201992.pdf

 

Thanks so much for your recommendations. I will check these items soon , and let you know how it goes. Alex

 

use a battery charger to fully charge your battery. disconnect the charger, and wait a few hours to the next morning. measure the battery voltage, it should be around 12.6 volts, give or take.

all measurements in DC volts, relative to chassis ground or the battery - terminal.

on the back of the alternator, there are two wires, a fat red one (B+) thats connected directly to the battery, and a thinner red one (D+) thats connected to the batt/alt light in the dashboard. with the key off, D+ should be 0 volts. turn the key on (without starting the car), the batt/alt light should come on. Measure the D+ terminal, it should be around 6-9 volts or so....

if the light doesn't come on and there's 11-12 volts at the D+ terminal, the alternator is likely bad. if the light doesn't come on, and there's 0 volts at the D+ terminal, then the problem is with the ignition switch or dashboard.

if the light does come on, start the engine, and the alt/batt light should go out, and you should read 13.8-14.2 volts at the battery +. if so, everything is working fine. if you read 12.6V or less, then the alternator is probably bad.

 

Hi Nichals - Could you tell me where this integrated fuse behind the instrument cluster is located and what it looks like. Is it obvious? Thanks again!

 

There is a strap screwed down to the board right below the speedometer. It looks like a wire but it's really a fuse. About one inch long if I recall

 

The fuse on the instrument cluster looks like a flexible plastic printed circuit board. If it is blown, all of the idiot lights plus the fuel and temperature gauges in the cluster won't work.

 

Just want to thank those who helped me diagnose my instrument cluster problem. I managed to get the cluster out (very tight fit) and found the little plastic flexible like fuse. It had obviously been burn't out. I did bypass it with a thin gauge wire, and what a treat! This solved all the gauge problems, as well as the charging problems I had. It's been a long time coming, as I needed to take a break away from this car after all the prior work and frustrations I had gone through the previous 3-4 months! Again, thanks for all the help with this!!

 

Glad to hear it! just be cautious as if something like that happens again you will no doubt need a new cluster.

If you want to be super cool you could get a backup preemptively, or. at least pull the fuse off a junkyard one.

 

Pierce, if dash lights come on when key is turned, but D+ terminal has a full 12.5 volts(equal to battery) what does that indicate?

 

that suggests that the diode board inside the alternator may be fried.

 

That's what I was afraid of. I just installed a new v regulator and brushes and nothing happened as far as charging. Ironically, I had a shop check the diodes 3 days ago when I had it apart and they said they we're fine. Does terminal D+ have it's own diode?

 

yeah, D+ is an input to the alternator that supplies the 'bootstrap current', while B+ is the output of the alternator that supplies the current to charge the battery.

typical bosch alternator schematic,

 

Wait a minute, now I'm confused(what else is new). I'm getting 12.5 volts from the small, red lead going to D+ terminal, while it's disconnected, which the diagram backs up. From the battery, thru the dash light and to the terminal, there's nothing that would drop that voltage. So where do you test to get 6 to 9 volts? Just to make sure I wasn't seeing things, I checked it again and got 12.5 volts. Then I connected it and back probed it and got 1.6 volts. I know those numbers are way off but how can it do that?

 

no, if the D+ lead is disconnected, you'll see full battery voltage on it. when its connected to the D+ terminal, you should see something like 6-9V on it (with ignition on, engine not running).

1.6 sounds really low. if you start the engine and let it warm up a couple minutes, whats the system voltage at the battery ?

 

I'll have to check tomorrow. But I'm pretty sure it won't increase and start charging. My dash lights have stayed on during this whole ordeal. BTW, this is why electronics confuse me: how is this possible(from volvoclub.org.uk) -

"You can test for power to and thru the bulbs to the alternator D+ terminal by taking the red wire off the D+ terminal and holding it to any engine metal (not the alternator itself) while a helper turns the Key ON and observes the warning lights."

Take a 12 v wire and ground it? Wouldn't that blow every fuse you have?
Also, if there's 12 volt coming to terminal D+ then why would you need to do this -
"Alternator Stops Charging: How to Get Home? My battery charging light just came on and I am far from home. Belt is fine. What to do? [Steve] No reason to be stranded because of this problem. You can get it home like this: Simply run a hot wire from the battery positive and connect it to the terminal on the back of the alternator....the one with the small red wire connected to it. This wire provides excitation voltage for the alternator. If you can get the engine started and then apply 12 volts to the excitation terminal, the alternator will charge. You don't even have to connect the wire. Simply touching the jumper wire to the terminal will cause the alternator to start charging, and remain so as long as the engine is running. If you did connect it, you will need to disconnect it when you stop the engine else it will drain your battery."

 

the D+ wire is not a straight 12V wire. its the dashboard battery light.

battery + --> ignition switch --> battery light --> D+

D+ inside the alternator goes to the field coil and that in turn goes to ground. there's a set of diodes to ensure that the battery connected to B+ can't feed out through D+, and so that the alternator itself can power the field coil once its alternating. the bigger mess of diodes are what turns the 3 phase AC alternator into a source of DC that the regulator regulates.

I think those indicator bulbs are 1.2 watts.. So, at 12V they are using 1/10th amp (volt*amps=watts), and 12V/.1A is 120 ohms resistance (volts/amps = ohms).

so when you take that D+ red wire and connect it to ground, you're just lighting up that light bulb, and only drawing 0.1 amp.

anyways, so when you unplug D+, and measure the voltage, you'll see virtually the full voltage of the battery. when its connected to the alternator, and the alternator is not spinning, the battery lamp is connected through the field coil to ground, and it lights up. when the alternator is running and generating power, then the bulb goes out, because connecting a bulb between +12V and +12V won't light up.

1.6 V with D+ connected seems a bit lower than I would expect, but thats still good enough.

so.... sounds like even tho you replaced the brushes, the alternator is still bad. unless..... if it has a weak ground, it won't charge the battery.

to test the alternator ground, start the engine, let it run a minute, then measure the voltage between the alternator ground (metal case) and the car ground (say, a valve cover bolt, or the battery - terminal). if you see more than a tiny voltage, the alternator isn't grounded well.

I had to replace the ground wire on my daughter's 240, it rotted through, looked just fine. was a short blue wire that was connected to a nut on the back of the alternator, and to the engine block. I replaced it with a piece of ground braid.

 

Thank you very much for the explanation. It kinda makes sense now. Here's an update: I forgot to install all the screws on the rectifier. So reassembled everything and ran the tests. Battery voltage is 12.5. Same at terminal B. Terminal D has 12 v going in and when connected it's 9.3 v. And B to battery and alt ground to battery and battery to chassis ground are all under .01 volts. The car started up and at idle the battery was still showing 12.5. I revved it up and it got to 13.7 and held that. But here's where I'm going crazy again. Yesterday all my dash lights came on and stayed on with no charging. Now, only the check eng, oil and srs lights come on and they all go out after starting. So i did the grounding test with the wire to terminal D and they all came on. I have no idea what's going on. If there was a fuse blown in the instrument cluster they wouldn't have come on. Anything that pops up for you?

 

Out of curiosity I took the Bosch 100 amp Alt out of my 940 and put it in the 740. Viola! It idled at 14 v and held that as I revved and the dash lights went out. One peculiar thing is that same alt in the 940 only goes to 13.6 and holds that. All accessories off yet the 740 produce 1/2 volt more?
Anyways, went to Pick n Pull and got a Bosch 80 amp off of a '91 240, popped it in and it is charging at 13.6 but the dash lights come on as expected when you turn to on but don't go out once it's running(SRS light flashes on n off periodically). The alt body has a good ground to the chassis so what could be happening internally to charge yet not turn off the lights? I could go bald trying to figure this out, which aint far away.

 

the important dash light to watch for alternator issues is the battery/alternator light.... again, it should come ON when you turn on the ignition, and go OFF when the engine is running. sometimes it will stay on after starting the engine but go out when you blip the throttle, thats OK too, as long as it stays off.

the other lights come on when you turn the ignition on as a ligth test, to verify all the bulbs are good, they too should go out when the engine is running, except as needed to indicate things like OD disabled, or oil pressure low, or whatever.