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OK, that nails it.
Here's how it works: IN "Bulb Test" key position, the warning lights that have good bulbs should be lit. Ever wondered what makes them turn off when the engine starts up?
The oil pressure sensor has a switch inside it that grounds the wire when there is no pressure. Engine starts up, pressure builds up, ground opens, light goes out.
The other ones, those that you see staying lit, get their ground side through the alternator brushes. Simply put (there are diodes in the circuit) those lights' ground side all go to that thin red wire.
It is one of the wires in the gray connector on the firewall (all of which are subject to crumbling insulation). From there the red wire runs in the main harness under the intake manifold and under the front of the engine, and connects to the spade lug on the back of the alternator.
So with the engine stopped, the lights ground to that spade lug, into a brush, around the rotor windings (where the current creates a small magnetic field), to the other brush, to the alternator frame, through the ground wire, to the engine block. Closed circuit, lights light up.
Engine starts, alternator starts spinning. That small magnetic field rotates, and creates electricity in the stator. AND, the ground is lost SO the lights go out. It is more complicated, but I cannot easily explain further, and this will do the job.
IF that thin red wire is grounded SOME OTHER WAY, like under the front of the engine where the metal harness holders can chafe into the wiring, THEN the lights stay grounded and lit, and the alternator does not get that small magnetic field and it cannot charge.
You can easily repair the situation. Put in a new red wire from the gray connector to the alternator. Route it along the firewall, down the RF fender and thence to the alternator. Use 16 or 14 gauge, try to use red.
The back of that gray connector can be popped open with care and a small flat tip screwedriver. The wire terminal in the gray connector is unique, clip it off and re-use it by solder/shrink tubing attaching it to your bypass wire.
The alternator end is a standard insulated .250inch female connector attached by either solder/shrink tubing or a crimper.
As long as you are at it, the black wire to the oil pressure sensor can be re-habbed in the same way. Be sure to route the wire and leave slack so the engine can move a bit and you can get in to change the oil filter and motor mounts.
This will do what you need. Given, of course, that I am not there with you looking at the territory. I cannot be responsible for that you do, unfortunately. There is always a possibility that something else is going on that neither of us knows about. Think things through, take things slow.
Good Luck,
Bob
:>)
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