Hi,

From your previous post:

"On both occasions, I pulled the D+ wire at the alternator and connected it to ground to be sure that wire was ok - and it is. The 4 warning lights illuminated."

This is at odds with the Volvo Charging manual: TP30729 see page 9

https://www.scribd.com/document/428674092/Charging-System-Fault-Tracing-Service-Manual-TP-30729-1984-VOLVO

Here's the temp info that Art referred to. I didn't find this temp sensor in the
940 and it's unclear what models have it.

pg 7
The regulated voltage varies with the tempera-
ture of the regulator . As the temperature of the
regulator increases, the regulated voltage
decreases . On same 1985 and later modeis, the
regulator is connected to a temperature sensor
located beneath the battery tray; thus, the regu-
lated voltage is more precisely matched to the
system's immediate requirements.

pg 9
Avoid grounding the field circuit (D+)
between the alternator and the regulator.
Grounding the field of either alternator or regu-
lator may damage the regulator.

Don't ground the alternator output terminal (B+)
as this may damage the alternator, the circuit.
or both. This precaution must be followed even
when the system is not operating, because the
output terminal on the alternator is "hot" at all
times. Terminals must be covered with insu-
lating boats or tape.


Check voltage drops

Positive Circuit Test

Connect a voltmeter across the alternator B+
terminal and the battery's positive (+) terminal.
Run engine at 2,000 rpm.
Load the alternatar by turning on eleetrical
equipment such as headlights, fan, and window
defroster, etc .
Observe the voltmeter.

Lower than
.3 volts Proceed with
negative circuit
test

Higher than
.3 volts Proceed to C10

Negative Circuit Test

Connect a voltmeter between the frame of the
alternator and the battery negative terminal.
Run engine at 2,000 rpm .
Load the alternator by turning on electrical
equipment such as headlights, fan, and window
defroster, etc .
Observe the voltmeter.

Higher than
.2 volts Proceed to C1O

Lower than
.2 volts Drop OK


C10
Eliminate (reduce) voltage drops

If necessary scrape and clean battery terminals.
Tighten battery connections.
Check ground leads between battery, engine,
and body.
- Check B+ terminals on starter and alternator.
Repair or replace leads as necessary so that the
positive voltage drops are less than.3 and negative
voltage drops are less than .2 volts.

The manual shows the wave forms to spot bad diodes with a scope.
It shows how to check output with a carbon pile and ammeter
and other tests.

Dunno if there's a newer charging manual?

Good luck, Bill