re '86 DL 240 wagon here. The alternator either died or started dying almost two months ago and I sought advice here. A few brave souls responded with a lot of useful information but get this; I've been through two remanufactured and one new alternator and still haven't fixed the problem. I've learned a lot about alternators and my wiring system in that time. I've checked all grounds. Re-routed the D+ wire from alt to firewall junction box. The alt warning light does go on in key position 2 and goes off when the engine starts running and the alternator starts spinning - (light goes off even when engine starts and alt isNOT charging. Is this a clue? ) but still no charge.
On rebuild #2 I got a slow climb to 14 volts but then it stopped charging. When I tested the diodes on that alternator - while it was sill hot from spinning, I got the reading of bad diodes. So I got a new alternator but got nothing. All of these alternators were Auto Zone and I had them checked after they did not work on their test equipment which said the alternators did work. I went to a competing parts store and had them test the last alt and it scored positive - but would not charge my battery. I did a parasitic draw test on the fuses and discovered the radio - which has never worked and only made squaks - was drawing energy from the battery so I disconnected it completely from the car.
So - now I'm tracing the D+ Circuit from alt to junction box at firewal (A in diagram) , to

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to battery charge warning light, to fuse 13 and out fuse 12 to key to key to whatever that box with four dots between the key and the battery + - to make sure this circuit is running ok. I'd like to know authoritatively what the Volt reading is on the D+ post on alt so that I can see the same voltage all through the circuit. Someone said it should be between 7 and 9 volts. But mine so far has read exactly the charge of the battery on both alt posts (B+ and D+) tho once it read .54 Volts. With key in position 2, I get no continuity on fuse 4 for the in tank fuel pump. Is this normal? I'll test the in tank pump to see if it is working but after that I don't know what to do. I've been banned from Auto Zone - they gave me a full refund and more or less said don't come back! The alternator circuit is pretty simple. Why is this happening?

Yes this is the famous '86 edition with the biodegradable wiring. Yes it causes all kinds of problems. I already know that. What I need to know is how to make the wiring circuit outside the harness. The wire from the D+ post of the alt is good once inside the harness - after that wiring is mostly internal (not exposed to melting elements) - wire from D+ to warning light - to fuse - then not sure - back to battery + post? If I rebuild the circuit it should work?

 

1986 is in the range of years that Volvo used biodegradable wiring insulation. Do you know if the main wiring harness has been replaced? If the wiring harness is original your likely to have all kinds of electrical issues until it is replaced.

 

Yeah, bad wiring can make for all kinds of crazy symptoms... Hard to say.

 

the D+ wire goes from the ignition key to the ALT lamp in the dashboard to the D+ terminal on the alternator. period.

the B+ lead of the alternator is connected to the big stud on the starter motor, and that in turn is connected to the battery+ via the big heavy cable.

when you turn the key on there should be a voltage (less than 12V, probably somewhere from 5-9V?) on the D+ terminal of the alternator relative to ground.

when the engine is running, the B+ terminal of the alternator should be around 14V relative to alternator ground. B+ and battery + should be identical. alternator ground should be 0V relative to battery -

 

Pierce - Since the wire from the D+ post on alt basically feeds back to the + post on the battery - shouldn't it be possible to connect the D+ straight to the battery, bypassing the warning light and key - and get 14 volts? This to prove the alternator is charging regardless of the circuit. I did this on the last alternator and got nothing.

 

yes, you can jumper D+ to B+ but do realize that will flatten your battery when the engine isn't running, so remove the jumper as soon as you're done testing.

 

OK. So this should have worked and didn't on the new alternator.

 

Make sure that the ground wire for the alternator has zero ohms.Set meter to ohms. touch one lead to alternator body. one lead to ground on body. Meter should read zero. If not after disconnecting battery remove ground from alternator. Remove ground connection from block. Measure wire as to ohms. Clean both ends up, clean block mounting area. fasten to block. check ohms. fasten to alternator . check again.

That's what got me.

 

better than reading ohms is to start the car, and measure the VOLTAGE between the alternator body and the engine block ground, and the battery - terminal. anywhere you see voltage ground to ground when the car is running means there's a bad ground in between.

 

Thank you.

 

Hey Zombie - I'm embarrassed to report that my alternator problem of a year ago was probably that I had the tightener mechanism upside down, so that it would only tighten so far and then not. This coupled with a glazed belt was just not turning the alt fast enough. But oddly, I went to a junk yard and got a used alternator and at that point discovered the upside down tightener and got a new belt and it's worked fine ever since. But now I'm having all kinds of electrical problems because of the biodegradable wiring harness. The latest was a screaming sound when the car was running. I fathomed it was the hot wire to the starter NOT turning off so that it was running while the engine was running. It was the sound of the starter winding down on shutting off the car that gave it away. Solution; I made a loop of wire in that hot wire to the starter and put a switch on it - so now I have to turn on the switch when I turn the key and shut it off again. It doesn't seem to stay hot every time but I figure the starter is now half burned out so I'm playing it cautious. On top of that - my headlights won't go on - but the high beam will come on, on pulling on the turn signal arm - so - if I need to travel at night which isn't often right now, that's how I get lights. And the windshield wipers stopped working. Phew. I need to place a new wire from command to activation on each of those items. But - the engine runs great and the tranny is fine . . . the car has a few years left - and it better as I have to get through a N New Mexico winter in order to rebuild a Toyota truck I have. And . . .