1979 volvo 242 DL. Oil Pressures warning light only comes on when the car is off. I can only see the light at night however, because it is not bright enough during the day. Starting the car, all the warning lights come on and go off once started like normal. I have searched high and low for a solution before tearing apart the instrument cluster. I believe it is a bad bulb...??

Hopefully someone with experience on the older 240s will post on this.

My guess is there's a short in the wire harness that curls under the timing belt cover. That harness carries the oil sender lead, as well as the "tickler" 12V lead for the alternator. That's the small red wire to rear of alt. Not sure if the main 12V lead for alternator output is in the same harness. Same for the alternator's ground - might be there too.

Grounding the oil lead with engine off shouldn't give any battery drain as it's only powered with ign. switch on. But hot voltage has to be leaking in from somewhere, and harness under the alt is my guess.

From early 80's through '87 many 240s had self-destructing wire insulation. You may have that, or the insulation might just be bad from age - nothing is forever.

For the '80's cars with that problem, the cure is usually to run fresh wires directly from the connector on the firewall to where they need to go. I don't have the complete road map for that; and also can't promise that your locations + wire colors will be the same as the "newer" cars either.
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Sven: '89 245 NA, 951 ECU, open-front airbox, E-fan, 205/65-15's, IPD sways, E-Codes, amber front corner reflectors, quad horns. Wifemobile '89 245 NA stock. 90 244 NA spare, runs.

That was the cause in my case. The thick red cable underneath the alternator bracket had corroded, and the heat had partly melted through to the thin red warning light wire and the oil pressure sender.

Check for a dirty / corroded oiled over oil pressure switch connector. The light should come on full brightness when the engine quits running.

jorrell
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92 245 245K miles, IPD'd to the hilt, 06 XC70, 00 Eclipse custom Turbo setup...currently in pieces

So the oil light should be on all the time when the car is off? This started happening about a month ago and never before. I am no concerned with the brightness of the light but rather why it is coming on AFTER the car is off.

Light on with IGN. OFF?

Or only after you shut engine off and turn key to "on" without starting it?
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Sven: '89 245 NA, 951 ECU, open-front airbox, E-fan, 205/65-15's, IPD sways, E-Codes, amber front corner reflectors, quad horns. Wifemobile '89 245 NA stock. 90 244 NA spare, runs.

Oil light only comes on when the ignition is off, once i turn accessories on it goes off.

Then I'm still with my first theory: short in wire harness that curls under the timing belt cover. Or at least a short somewhere. I don't think they'd wire that circuit to be live always.

See my first post if you didn't already.
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Sven: '89 245 NA, 951 ECU, open-front airbox, E-fan, 205/65-15's, IPD sways, E-Codes, amber front corner reflectors, quad horns. Wifemobile '89 245 NA stock. 90 244 NA spare, runs.

Thanks Sven's Maintainer. The wiring harness that includes the oil pressure sending unit and the hot wire from the alternator to the starter were all melted and touching the engine block. So I cut the bad part out (about 2 inches) and spliced the big red (from alternator to starter) and the black oil pressure wire.

Oil light is gone and also corrected the terrible warning light delay on cold mornings-which is a fact of life in Montana.