I've tried everything conceivable to get a new (4th) tested, alternator to charge a new, tested, battery. Checked all resistances, grounds, dash light works etc etc. So - my question at this point is - since the '86 charging system is NOT hooked into the computer but is mostly an independent circuit - (batt/starter/alt - D+ exciter wire to dash light )- could the throttle position sensor - if it were bad (car runs fine just doesn't charge the batt.) somehow inform the regulator to NOT produce voltage? I'd like a second opinion on this before I go to the junk yard. I saw a situation like this solved on a YouTube video - which led me to clean the entire TPS - nothing changed. Thanks.

I only get 1.5 V's from D+ with car running; tried jolting the D+ wire with a separate wire straight from the + post on the battery - no go.

 

a standard bosch alternator has ground, B+ heavy red wire to the starter and on to the battery, and a skinny wire from the dashboard alternator light goes to D+

D+ is an important part of the circuit, it provides the bootstrap current so the alternator can generate power.

I test it with a digital volt meter. for instance. car off. measure battery voltage, should be like +12.6 if its a fully charged battery at rest at 68F. start car, measure voltage again, should be 1-1.5 volts hire than the off reading, like 13.6-14.1 volts. If so, your alternator is working and charging the battery, done.

if you still only see 12.x V or whatever you saw before, put the red lead on the battery + and the black lead on the body of the alternator or its ground screw. do you read 13.8 or 14.1 or whatever volts? then your ground is bad.

switch the car back off.

turn the ignition to II (run) without starting the car. the dashboard red 'alternator' or 'batt' light should be lit. take your volt meter, and measure the voltage from engine ground (fuel rail ground screws?) and the skinny wire D+ terminal on the alternator, you should see about 12V with the key on but the car not running.

if the light doesn't light, or you don't see 12V at the D+, then you need to fix that (dashboard lightbulb, ignition switch and wiring to dash light to D+)

 

Thanks for the detailed reply. However, as I mentioned in my post, I only get 1.5 volts at the alternator D+ post with key in position II or even with engine running, alternator spinning. Either that low charge - or something else is preventing the alternator from putting out 13.5 to 14.5 as it needs to to charge the battery. There is not a ground problem as I've done the test you kindly describe - testing the alt casing against the battery ground.
This is why I've come to the point of asking IF the throttle position sensor could be malfunctioning and sending a signal to the regulator in the alternator - that there is no need for the alternator to put out a charge - if the TPS is telling the alternator it's in idle for instance. ( I came across a YouTube video where this was the problem on a 240. In that case, the TPS simply needed to be taken apart and cleaned. I cleaned mine and there has been no differance.)

 

Ive never have had a problem with my Volvos. But I have a Ford expedition that I had to rewire that was doing same thing you describing. I never figured out why it wasnt getting enough signal to excite the alternator. I ended up rewiring the alternator and has worked like a charm ever since. To be honest it could be alot things, these old volvo are known to have wire gremilins in them. I did have to rewire my fuel pump, just pulled my back seat and had a burn spot on the bottom of the seat. I was lucky that the car didnt burn.

I was thinking you could use the detailed info to rewire your alternator. I shouldnt be to bad to rewire. At least it would get you back on the road.

 

if the batt/alt light is lighting when you turn the key on, then your alternator is getting trickle current to start. 1.5 volts sounds a little low but not nuts (I thought it was supposed to be more in the 5-9V range, but I've not measured it in a long time).

and no, there are NO connections to the alternator other than B+ from the battery by way of the starter, D+ from the batt/alt light in the dash, whihc in turn is powered from the igntion key and that from the battery, and ground to the engine block. the idle switch ONLY connects to the fuel injection so it can manage the idle air control valve when you're off the throttle.

 

Are you sure the ignition switch is good. Did you hot wire the alternator to by pass the ign. This seems to be to simple of a problem to be spending this much effort on.

 

First of all, you should have 12v on D+ coming from the Ign. Sw.
Remove the D+ wire from the alternator and measure the voltage at the wire, if it is still 1.5v on that wire you have an issue at the ign switch.
To confirm alternator output put a jumper wire from B+ to D+ and start the car and check the voltage at the battery for at least 13.8v.
The D+ voltage is a reference voltage for the regulator and also feeds the windings in the rotor. (the part of the alternator that spins). 1.5v on D+ isn't going cut it.

 

no, D+ should *NOT* be 12V when the ignition is on but the engine is not running, it should be something significantly LESS than 12V, as its a resistance bridge.

12V+ (from battery
....ALT light bulb (a resistor)
.......D+ terminal
.........alternator bootstrap coils (more resistance)
............ground.

the voltage of that circuit should be something like 12V / (Rlamp / (Rlamp + Ralt))

last time I looked at one, I think I saw 5 or 7V or something.

if the ALT light goes on with the ignition key and off when the engine starts, the bootstrap circuit and alternator are probably working OK.

 

some alternators will 'self excite' if you rev the engine to 2-3000rpms. did you try that?

 

I stand corrected, voltage at D+ with engine off is 6-9vdc according my manual (also when out to my 89' 740 and measured with my meter), battery voltage at D+ with engine off would indicate a bad alt.

 

Thanks for the info that the voltage on D+ should be 6-9V but I think you meant to say with key in position 2 or with car running and not 'with engine off'. Mine has consistently been 1.5 which is very low. This leads me to wonder if the cable from the starter to the alternator is shredded and not carrying enough voltage to the alternator for the D+ to be so low. I've checked every single possible other thing and still no charge.
The reason I mentioned the throttle position sensor is because I saw a video on YouTube where an alternator wasn't charging - all evenues were explored - and the guy finally decided it was the TPS which he dismantled and cleaned which did then did allow the alternator to charge. Is that crazy?

 

the throttle position sensor has *NOTHING* to do with the alternator on these Volvos. maybe on some other more modern computerized cars.

are you sure the D+ wire is connected to the correct terminal on the alternator? many alternators have an extra terminal, which is used for a noise suppression external capacitor (optional).

 

Good picture pierce now if the OP would disconnect the small red wire and tape it off and then run a jumper from the big red wire to the small red wire terminal and start the car. Also make sure the ground wire is grounded to the block. Now with the car running what is the voltage at the battery.

 

Pierce - Thanks for considering my monotonous problem. Yes I'm sure I have the right connections - the current new alternator doesn't have the connection for the capacitor - only B+ , D+ and ground to casing bolt so it's hard to go wrong.
Thinking the D+ should read 5-9 V's - as your manual and your Volvo read, and not 1.5 V's as I get - I bought a new fat cable for the connection from the starter to the alternator B+ post, and disconnected the old cable in case it was rotten (copper doesn't rot) - no change.
Is it a clue that on this alternator and on one of the other new ones I tried, on installing the alternator and starting the car, those two alternators STARTED charging but then stopped and didn't do it again. Why????? Why Lord Why? Why me????

 

Jagtoes - Thanks for replying. I tried that - disconnecting the D+ wire from alt. and running a separate wire from the B+ post of the battery to D+ post of the alt. - no action. Also tried alligator clipping D+ post to B+ post. No action.
Is it a clue that two of these alternators STARTED charging but then stopped and didn't do it again? What would have signaled their regulators to NOT charge?
PS. What's an OP?

 

OK I assumed you removed the D+ wire and left it off and then jumped the D+ to B+. After starting the car and running it up to 1200-1500 rpm and let it settle to idle what was the voltage at the battery. If more then 13.5 then the alternator is good if not then it is bad. If you buy a replacement alternator at an auto parts place just have them put it on their tester and also read the output voltage at their store. It should be 13.5 + and if it works there then it will work in your car.
OP = Original Poster

 

a working alternator should be more like 14.2V .... 13.8V is the bare minimum to fully charge a lead acid battery. if the battery is deeply discharged, then the voltage will be somewhat lower until the battery is fully charged.

 

Just using round numbers. Tring to verify if the unit is charging when tested at the auto store on their tester. If it shows charging there then unless he has a major wiring issue it should work in the car. I agree on the old style alternators 13.8-14.5 is the normal charging range. I would suggest he charge the battery and then put the alternator in the circuit.

 

This seems to be far weirder than anyone is getting. I had this 4th new alternator tested before I left the store. I had the other alternators tested after i bought them and couldn't get a charge. I had the new battery tested. with the engine running and alternator spinning, I only get the exact same voltage as the battery currently has as it's draining from the car running - no charge at all. Something is informing the regulator to not charge.

 

i got a lifetime alternator at autozone which did not charge when installed in a vw golf. took it back to autozone tested good on their bench. took it across the street to an advance auto shop and it failed miserably on their machine.... got another one from autozone no questions asked...
so... you may want to get yours tested again somewhere else.