Hey guys thanks for all the help, I removed the regulator and brushes and checked them out, they were about 3/8 in length. I rewired the small red to the firewall, and now everything works great. Thanks again.

"I get the battery light when the key is in the on position, I checked the wires coming off the alternator and had to repair the small red wire (not the b+). I checked the ground and it is good also."

I don't know what is causing the failure, but getting the Battery Light* says that the thin red wire, voltage regulator, brushes, and ground wire are providing the necessary ground path for the "preexitation current" the alternator requires.

I'm not real confident in parts store alternator tests, and would be inclined to try a new brush/regulator unit if the present one's brushes are down to 1/4" or so.

* In addition, you should also see the Brake Failure, Parking Brake, and Bulb Failure lights at Key on. These 3 are diode-connected in parallel with the Battery Light when starting, to provide increased preexitation current to the alternator (apparantly the current thru the Battery Light alone isn't enough).
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Bruce Young
'93 940-NA (current) — 240s (one V8) — 140s — 122s — since '63.

That small red wire is the key.

when you get the key into Position II, also known as "Bulb Check" position, or "Run" position, the warning lights should light - except any burnt bulbs.

Now, when you start the engine, ask yourself "why do the lights go out?"

The oil light lights by virtue of having the ground side be through the pressure sensor on the block. No pressure = light, and otherwise otherwise.

The others are not so simple. They are grounded through that small red wire.


Ground side from bulbs to gray connector on firewall - slot #3 for D+/61, red.

From that connector to the main harness to a branch harness that runs under the front of the engine. Look at the wires coming up between the alternator and the block. Fat red, thin red, and black.

Black is the oil pressure sensor. Fat red conducts heavy charging current from alternator to battery via the starter.

Thin red, when key is in "Bulb Test" position (engine not running) has a small voltage on it - what's left after coming through the warning lights.

That wire provides ground for those lights through the rotor wiring of the alternator. That small voltage provides initial excitation for the alternator, without it the alternator will not charge. When the alternator begins spinning and generating the ground is lost so the lights go out.

If that wire is open, no warning lights at all and no charging. If it is grounded some other way, the warning lights don't go out, and no charging.

If the wire is sometimes grounded, maybe due to being just a little messed up under the front of the engine, you get an intermittent problem.

The 1984 240s have the crumbling insulation problem, which includes ALL the wires from that gray connector. Replace and re-route. Red and black to run allong the right side fender and then with lots of slack to their destinations.

Check archives and/or FAQs for more details.

Good Luck,

Bob

:>)

PS: The other two wires are yellow to temp gauge sender, and BL-Y from key to starter solenoid.

"Where does that wire connect to so i can rewire it?"
The harness goes under the front of the engine and back up to the gray plug on the firewall. The wires are often visibly degraded there.

You could rewire the red wire from the gray plug and run the wire along the inner right fender instead of through the harness. Same applies to blk oil wire.
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1980 245 Canadian B21A with SU carb and M46 trans

Check the alternator brushes; the brush assembly comes out by removing two screws on the back of the alternator. Both brushes should be at least 3/8" long. It is easier to reinstall the brush assemble if the alternator is on the bench. Check the condition of the slip rings too. The chain part stores will bench test alternators for no charge (call first to verify this is still offerred. jp

Check the wire loom that passes under the engine behind the pulley. Alt to batt, red wire and oil sender wire are inside and its the most exposed/prone to failure.