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240 chasing a charging issue


New member
May 21, 2019
( i finally convinced my wife to make it her daily driver instead of buying some used junk so i gotta get this thing charging!!)

my 1991 240 wagon, was sitting 3 years and i put a new battery in her and she faithfully fired up. i slapped a temp tag on her and drove her 20 miles until i had to clean the mouse nest out of the air filter and drive the other 25 miles to our new home. new air filter, rebuilt window motor, can of seafoam and a handful of various bulbs and i drove her to get her inspection. when i went to drive my newly passed 240 home she tried to crank but didn't have the juice... the inspector gave me a jump and i got the old girl home. i figured it was probably the alternator that had gone bad so i looked around and got me a rebuilt one from a auto parts store. put it on that night jumped her off and let her idle a while while i cleaned the interior. the next day i get a call from my distressed wife that she is stranded at the grocery store.

when i get home i put the multi meter on and the alternator is only putting out 12v but when i take the leads off of the battery it reads 14.3v. i test it several times in various locations however the results are the same (with a variance of .3 or so) i take the battery out and take it to go get tested at an auto parts store. they say its good but dead and will charge it for me and test it when its full. i go home and take the alternator off, clean and inspect all connections everything is a-ok. i pop a different battery i have in and the same thing is going on. i head back up to the store grab my newly charged battery and replace it into the 240. the fella there checks it out and says my voltage regulator is failing.

from what i understand the VR is built in to the back of the alternator, i just bought a re manufactured one, before i go accusing some poor shop keep of selling me a bum alternator does anyone have any advice or has any one experienced anything similar.

also i saw the mouse today, he is still in the engine compartment.

thanks to anyone who read my short story :-P
First off - when you first turn the key on (engine off), is the alternator warning light on? Does it go off when the engine is running?

I had weird things going on with my 240's charging system for a long while - it ended up being a *TINY* flaw in the printed circuit on the back of the instrument cluster.

The alternator gets 'excited' (in an electrical sense, lol) by the current from that alternator warning bulb. It flows from another source on the board, through the bulb, along a printed circuit to a plug, and then through the wiring loom to the alternator. For fun's sake - the circuitry on the instrument panel can still feed "12V" to that wire even of the printed circuit has failed, or the bulb is burned out, but it's back fed through several circuits and the amperage isn't quite enough to reliably light off the alternator. But it will test as '12V' if you use a multimeter on it to test it - as long as it's unplugged from the alternator. Plug it in, and the load from the alternator will make the voltage drop down to nothing.

Another couple of shade tree tests:
1) If the alternator light isn't working, try taking the exciter wire (the small one, lol, not the large one) off the alternator and grounding it. If the warning light circuit is working properly, the alternator light will come on. If it's just getting back fed, several other warning lights will come on instead.
2) With the engine running (obviously, be careful) try using a jumper wire to put 12V onto the exciter terminal - only needs to be done for a second, and see if the alternator will start charging.

Here's another thread discussing 240 charging issues: http://forums.tbforums.com/showthread.php?t=279601
thanks for the quick reply!!



this is key on not running and running, im going to go jump the big wire to the little wire on the
back of the alternator now, and then ill try the excitement wire next. (sounds fun! ;-) )
well i guess i dont know how to post pictures, however, when the switch is on service, check engine, alternator, oil pressure, parking break, break failure, bulb failure and upshift are all lit, when i start the car only up shift remains
alright so i placed the excited wire on a ground on the back of the alternator and while i was doing some of these things i noticed only the check engine light, oil pressure light and upshift were staying lit. i hooked everything back up normally and see that all the other lights are not quite as bright as the CE OP and US lights. looks like a issue with grounding, but where do i start looking?
i jumped the post of the little excitable wire to the post to the less excited big wire and i think my voltage went up .3ish it was at 12.9 and i cut the car off and fired her back up, she was only putting out 12.6 then. also it may be worth noting at some point this morning i was geting voltage in the 13's but only for a bit before i put her up on the ramps.
aight yall im off to work but i have all day off tomorrow and a 6 pack in the fridge. so if yall come up with anything im super grateful. ive been using this site for years to keep my wagons on the road but this is the first time ive actually made a thread and its kinda awesome. so thank yall so much.
Here's my advice:
Get a multimeter that can read AC and DC voltage.

Preliminary tests: check alternator belt, and belt tensioning mechanism. Alternators with slipping or loose belts won't charge.

Test 1: Voltage Regulator / Diode Pack Test
With car running, place multimeter set to AC VOLTAGE across battery terminals. Reading should be very small. If more than +-0.5V RMS AC voltage, you have faulty diodes, and either the voltage regulator or internal rectifier of the alternator needs to be replaced.

Test 2: Positive Battery Cable Resistance Test
With car running (it's ideal to place your test probes before starting the car to avoid hand in the belts etc) and multimeter set to DC VOLTAGE, place one probe on the B+ terminal on the alternator, and place the other multimeter probe on the positive battery terminal. You may need wire extensions to reach both, my multimeter's wires weren't long enough. Any voltage reading greater than 0.3V should cause concern. Anything less than 0.1V is ideal. If 0.3V or greater is measured, repeat test between battery positive and starter positive, and again between starter positive and alternator B+ to narrow down the faulty cable.

Test 3: Alternator Rectifier Resistance Test
With car running, and multimeter set to DC VOLTAGE, place test probes on the D+ and B+ terminals on the back of the alternator. Any reading greater than 0.1V is cause for concern. A measurement less than 0.1V DC is ideal. If the reading is greater than 0.1V, the alternator has a faulty rectifier (which cannot be easily replaced by the average DIY'er), and the alternator should either be taken to an alternator repair shop or replaced entirely.

Test 4: Alternator Ground Resistance Test
With car running, and multimeter set to DC VOLTAGE, place one test probe on the negative battery terminal, on place the other on the aluminum body of the alternator. Be sure to use the sharp point of the electrode to dig into the aluminum body of the alternator because the surface will be oxidized and not very conductive, and may give a false reading. Any measurement greater than 0.3V is cause for concern. Measurements less than 0.1V are ideal. If more than 0.3V is observed, repeat the test, but from the negative battery terminal to a bare piece of metal on the car (engine ground cable is a good one). If more than 0.3V is observed here, your negative battery cable is bad. Repeat the test also for the alternator aluminum body to engine metal. If more than 0.1-0.2V is observed, replace the alternator ground wire (short and small wire from body to engine).

If all the tests are passed, but issues still follow, the issue lies somewhere more obscure. Most alternator/charging failures can be diagnosed with the above tests.
Those tests mentioned are VOLTAGE DROP TESTS. I do them commonly. It's a great way to test the cables and connections.

The ground wire and the exciter wire going under the engine on these cars commonly fail. The brushes too.
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Forgot to mention the brushes. If the system is running, and the previous tests have passed, and alternator still isn't producing voltage, brushes could be suspect. Hard to test for those with a multimeter. If the unit is spinning, and all grounding and battery cables are correct, and both D+ and B+ are producing (the same) inadequate voltage, and there's no AC attenuation, it's likely brushes or very damaged rectifier.

ZVOLV, yes they are voltage drop tests. That's pretty much one's only capability when one owns a multimeter, but not an oscilloscope or alt bench tester.
Lots of times the alt is pushing correct voltage out, but losses downstream make the battery only see some of the voltage. So since he's seeing occaisional 13V readings, the alternator is doing something, we just don't know if something else is eating the volts or if the alternator is slacking to begin with.
wow! thanks for all the great info, and its just what i need... im so bummed out and beat down that im thinking terrible thoughts about used hondas and scrap yards.. lemme explain.

i went to the advanced where i bought the rebuilt alt, took it off and had them bench test it. those fools tried and tried for a half hour to test the thing but they couldnt get it do spin up and eventutally told me that the alternator had a faulty internal ground... ( wtf? ) so they issued me a replacement however they didnt have one and the next store that has one closes in 30 and i have my alternator in my hands... so we find another at a location 40 miles away and wrench in hand off i go.

we get there and those guys are super helpful grab me the replacement alt put the old pully, fan and capacitor on it, throw it on the bench tester and see that it passes all tests... TWICE!

brimming with excitement i rush to lay on my back and shove this new equipment in my 28 year old not so faithful 240.

all hooked up and i grab the multi meter... 12.5...

head hung in shame the shop keep checks up on me and asks " did we get it man?" "yessir" i lied. i got the old girl back home and ploped down at the pc to check turbo bricks, thank yall a bunch im gunna get this thing charging.

i gotta work early in the morning but after work i will be testing for voltage drops along those most common routes. it has to be in the wiring right? the alt checked out, i had the battery tested the other day, it checks out.

also i have a question, will any wire work for extending my multi meter, i have bell wire and braided speaker wire. maybe 16 Ga? or do i need to purchase something with alligator clips? sorry for the essay
My guess is that the big fat ground wire from the alternator to the engine block is bad. This would match your good voltage when battery is disconnected (alternator not under much load), but bad voltage when battery is connected (alternator trying to re-charge battery).

If you look at the alternator, there should be a short wire from the alternator body to a nearby engine mount bolt, it's blue on mine. Check that both ends are firmly in place and try to flex it a bit to feel that it's intact. Or do Ian's #4 check.

For measuring voltage, almost any meter extension wire is fine. The meter draws almost no current so even the tiniest wire will be fine for a meter extension.

Edit: I reread the earlier info, and I guess it could also be a bad/poor +12v wire from the alternator to the starter (and then to the battery). This is the big red wire that runs from the alternator, around the bottom front of the engine, to the starter. It tends to get beat up over time.
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that ground wire i actually broke the conection off of when i was taking the alt off for the 4th time lol, so i had to get a new end and put it on. ill take the whole thing off tonight and inspect it (if it stops raining by then) somhing ive noticed but hadnt thought much of is that the alternator seems to be eating the belt. theres belt dust build up near it and the belt is noticeably thinner than the others. also should i have 2 belts around it?
well yall i finally solved it. and im an idiot.it was a bad battery all along. it was bought new and tested several times at auto parts stores but when i took the battery out of my scion and put it in the volvo it is charging that battery at 13.6

thank yall for trying to help this fool.
well yall i finally solved it. and im an idiot.it was a bad battery all along. it was bought new and tested several times at auto parts stores but when i took the battery out of my scion and put it in the volvo it is charging that battery at 13.6
thank yall for trying to help this fool.

It wasn't a waste if you learned something about your car. Plus it's a good thread on dealing with alternator issues.