That's a good simple approach. thanks. However my car is parked outdoors and it's around freezing so hopefully the proportional difference will be apparent. So far I have tested the new alternator to the new, fully charged battery and it was too low. I suspect a dead wire lead from the D+ point on alt. something you pointed out - replacing that wire on your 240's that went under the engine - with the biodegradable wire ( I'm '86 240 DL) - so I'm going to follow the map you laid out and trace the wire from pin to pin.

 

yeah, basically, whatever the batteries rest voltage is, the charging voltage with the engine running should be about 1.2-1.5 volts higher.

 

Pierce - I'm baffled - again - I get equal voltage out of the battery + post and the D post on the alternator - when the engine is running - but if I hold the voltage meter on the battery + post for a while, engine running, the voltage is slowly going down - so I don't think it's charging. The battery icon lights up with key in position 2 and goes off when the engine starts running - this supposedly means it's charging. Also, if I put the volt meter on the alternator ground wire I get a minus reading. What could that mean? So - I'm going to try and track the D+ circuit.
You wrote; starting at the ignition switch pin 15, a red/black wire goes to pin 3 of connector '233' (the 3 pin connector on the back of the speedometer), that goes to the battery/alt bulb, then a red wire goes from pin 11 of connector '31' (the full circle connector on the back of the instrument panel) to pin 3 of a 2x4 pin block connector near the center of the firewall, and a red wire from that pin to the alternator D+ (exciter) terminal.
Is that '2x4 pin block connector' on the engine side of the firewall? It's black and about 2 1/2" by 3"? Has about four wires going in and coming out? I'm thinking of replacing that whole wire to D+?

 

ok, with the engine running, volt meter (-) probe on battery - terminal (try and poke the actual terminal, NOT the clamp), and volt meter (+) probe on alternator ground... if you see ANYthing other than 0.0V, you've got a bad alternator ground. fix that before proceeding with anything else.

 

oh re that connector... if its got a red wire on pin 3.... with the volt meter (-) probe on a good ground, and the ignition off, check the voltage at that pin (by stuffing a probe into the back of the connector shell), you should see very close to 0V. switch the ignition on without starting, you should see a voltage around 7-9V (less than 12, but well more than 0). start the engine, you should see alternator voltage (13.6-14.2).... if you see all this, then yes, thats the right connector.

question: *does* the batt/alt light come on with the ignition and go off when the motor is started ?

 

Ha! Great - you've laid out just what I wanted to know. Thks. And YES the alt/batt light goes on in key position 2 and then out when the car starts.!?! I'm going to scrub up and put a new electrical connector end on the alt ground cable as I suspect that my getting an equal reading on both B+ and D+ could mean the alternator is operating fine but the ground is preventing the charge.

 

So - I tested the red wire in slot 3 in the firewall box. 0 at key off. 1.44V (NOT 7 to 9 volts ) with key in position 2. 11.87 with car running. 11.87 is the level of charge I have after all this testing.
Confident that was the right wire, I replaced it from the D+ post on alt. to one side of the box.
Added a ground wire from a bolt on water pump to alt. Alt ground does read zero with - probe on battery post (not clamp).
The weird thing is that for a bit the battery was charging a bit- it went to just over 12 - but then started going back down. Ran the engine at about 4000 rpms with probes in place on batt.
The battery is new and has been tested twice while charging. the alternator is new and has been tested. The batt light does go on in key postition 2 and then goes off when engine running. Why did it charge that little bit? Baffled.

 

this is, supposedly, a new alternator? huh. maybe your battery is shot. anything below about 12.2V is too low.

 

I am having similar issue. I need to to solder as my wire is almost cut in half. Does anyone know what gauge is the alternator thick wire? oil sensor and other one is 16 gauge I believe

 

I would not solder that alternator wire, I would replace it. its very hard to solder wire that heavy and maintain a decent mechanical and electrical connection without burning the insulation.

I believe the alternator-to-starter wire on a 240 is 6mm^2... 6mm^2 is between AWG 8 and AWG 10. the battery to starter wire is 25mm^2, thats between 2 & 4 AWG. these two wires also could be 10mm^2 (6-8 AWG) and 35mm^2 (1-2 AWG), the diagram for a 1987/1988 240 shows both gauges, with the larger gauge in parenthesis.

 

Anyone try bypassing the instrument cluster and using a diode in-line to alternator? Check out this video

 

not sure why you would use a diode, the D+ iterminal already has diodes behind it, to replace the dashboard light bulb, you would use a resistor tied to the ignition power (circuit 15).

 

I tried a resistor first and it did not work

 

what value resistor? it should be equivalent to the light bulb, probably just a few ohms.

 

15ohm 12W, This is the one I tried

 

Looking at the video I couldn't help both laughing and feeling sorry for the idiot who did this. Then again seeing a fuel gauge plugged into the dash seems to make this a redneck volvo. Seems the work he did to patch the problem would have been better served in fixing the problem. I wonder how he does on brake jobs.

 

Haha well I did the same thing and it worked for me. Maybe not the most professional job but it only cost me $5

 

I know it 's an old thread, but I may be able to help someone. My car is a 1991 Volvo 240 Wagon. Same issues as far as new alternators, all voltages check out, all idiot lights work as they should. Still not charging properly, Well I finally traced it down to this relay that nobody talks about. Nothing wrong with the relay itself, but to the end of the wires plugged into it. It is a multi purpose relay with 4 prongs. 4 wires go into it, 2 are white and 2 are red. Cut the ends of the wiresnand redo the connections. Problem solved! Attached are some pictures. Note, not applicable to all years.

 

Old problem. fixed. Thanks!