While driving on the freeway in my 87 240, the oil pressure light lit up. The other dash lights came on too, but were very dimly lit. A short while later I noticed that the battery was losing power and no longer charging. The speedometer was fluctuating, gas meter wasnt working, headlights and interior lights dimmed. The battery is pretty much drained now. Any suggestions on what's wrong? Alternator? Wiring? thanks

Specific to the symptoms you give - it is the harness that runs under the front of the engine. The other posts are correct - up until 1988 the harness beginning at the 1"x2" connector on the firewall is a F disaster.

In your case: The oil light comes on when the lead to the sensor is grounded. The sensor grounds when there's no pressure - but if the wire get shorted to ground elsewhere you get the light. The harness under the engine front has two bendable metal clips to hold it in place, and over the years they can chafe all the way through to the wire conductors inside. Thus your oil light.

The alternator needs a little voltage to create current, and that thin red wire on the back provides it. When it gets grounded out or is disconnected, you get no charging. The fat red wire on the alternator carries the full charging current to the battery via the starter. It seldom goes bad, but if you go into the harness check it for really good insulation, it is ALWAYS hot and a ground short is a fire hazard.

The harness can be redone, or you can by-pass the faulty wires. They both originate at the 1"x2" connector. The red and the black ones. Many owners have just run new wires from the connector along the firewall and fender down to the oil sensor and alternator. Seems quite easy.

Good Luck,

Bob

:>)

I second Dan's reply. Recently while coming from the interstate down an on-ramp my '81 242 cut out and would not restart. Immediately I suspected the fuel pump relay when the pumps wouldn't run when I turned the ignition on. So I removed the relay and jumped the fuel pump connections and the car started but was low on power and the battery light was also on. None of the gauges were functioning besides the speedo. I didn't remeber the car ever acting like that when running with jumped fuel pumps and when I checked the relay it was fine. I looked at the fire wall connector of the wiring harness and sure enough the insulation was crumbling and the wires were shorting out. I made sure the wires were not touching and and attempted to start the car and it fired up and ran normally. I also used the liquid electrical tape to fix the bare wires but it seemed like as I put the stuff on more insulation was falling off in the process. So now I'm looking for a new harness as well.

Hope this helps,
Adam.

Probably the famous (or infamous) crumbling engine harness. They tend to crumble early and crumble often down near the alternator where the oil sender is.

The insulation has most likely crumbled off the wires and the conductors are touching (shorted) each other or touching the engine block. If not right near the oil filter and alternator, then possibly where they (together) loop under the front pulley in the harness.

Also examine the engine harness where it plugs into the main harness near the firewall. You'll see a gray plastic plug, about 1"x2". Look at the wires going toward the engine and see if the insulation is falling off. It was (is) on my '86 245, and I patched it using "liquid tape" from Radio Shack. About 4 coats, I think. That was in '96 and it still runs fine (even though I have a good replacement harness ready to go in some decade).
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Don Foster (near Cape Cod, MA)