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The warning lights, except the oil light, are grounded in Bulb Test positon via that red ting wire to the alternator. The oil light is lit when there is no pressure, the sender grounds internally.
The others are tied together, each with a diode so one won't mess up the others.
Engine stopped, the circuit completes through the alternator brushes. Potential across the lights is 12v. Engine running, the rotor windings are now making electricity, and potential becomes zero, the lights go out.
In fact, it's that small current coming to the alternator brushes that makes the necessary magnetic field for charging. If that thin red wire is either not connected (warning light off), or grounded someplace else (warning light on), no charging.
Since you got all the warning lights (again except oil) to act together, I think your problem is in the thin red wire circuit.
Have a look at the gray connector on the firewall, look at the insulation on the wires before touching it. Falling off? The harness may be your problem.
First fix is to bypass the stock harness for that red wire and also the black one that goes to the oil senser. Run new wires from that connector along the firewall and down the RF fender to their end points. You will need to use to terminations that are inside that connector. When you get the connector off its clip and unconnected, you will see that the back can be opened up and the terminations come out. DON'T MIX THEM UP.
There may be more info in the Archives on this, maybe in the FAQs.
Good Luck,
Bob
:>)
PS I have the Volvo Service Manual for wiring Diagrams for the 1984 240. It is an extremely helpful book. 1-800-25-VOLVO or www.volvocars.com/lit
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