Toyota - Celica :: 1986 - Tail / Brake / Battery Warning Lights Came On - Won't Charging

Problem with my '86 Celica's charging system. Car has about 135,000 miles and original alternator and belt. It is usually driven once or twice a week, but after sitting about 10 days, the tail light, brake, and battery warning lights came on when I started it. The lights went out after a minute. This same sequence of events happened the next three times I started the car that day. The fourth time, the lights went out but came back on as I drove. I found that revving the engine to between two and three thousand RPM made the light go off, but it sometimes came back on. And the engine revving isn't a sure thing now. Hit and miss. My wife and I have been trying to diagnose the problem.

When the warning lights are on, the dash voltmeter is near the bottom of the operating range. After revving and the lights going off, the voltmeter jumps up near the top of the normal operating range indicating the battery is charging.

The belt is checkered on the inside but not frayed. It deflected about 7/16ths inch midway between two pulleys about 17" apart. The Haynes manual said 1/2 inch was maximum deflection for that span. No unusual noises from the alternator.

We ran a checklist from my Haynes manual but I think it has an error in it. Here are the two steps that don't make sense. I marked the parts that seem to contradict with asterisks.

h) Disconnect the battery cables (negative first, then positive). Inspect the battery posts and the cable clamps for corrosion. Clean them thoroughly if necessary. Reconnect the cable to the negative terminal.
i) With the key off, insert a test light between the negative battery post and the disconnected negative cable clamp.

1) If the test light does not come on, reattach the clamp and proceed to the next step.
2) If the test light comes on, there is a short in the electrical system of the vehicle. The short must be repaired before the charging system can be checked.
3) Disconnect the alternator wiring harness.

(a) If the light goes out, the alternator is bad.
(b) If the light stays on, pull each fuse until the light goes out (this will tell you which component is shorted)."

Well, we decided that the last instruction in Step h should be to reconnect the POSITIVE cable (but could be wrong). I did this and we did Step i as written. The light came ON (Step 2). Disconnect the alternator wires at two points. Light stayed ON. Pulled every fuse under the hood and on the kick panel by the clutch. Light stayed ON.

The battery is near the end of its warranty period--about two-year old DieHard. Voltage at the terminals is about 12.4V with key out, about the same with ignition on but not running, the same with engine running and the dash lights showing, and about 14.5V after I get the dash lights to go off and the battery starts charging.

So, we're at a standstill. Tests say the tension on the belt is okay. The test light testing indicates the alternator is okay and the test light stayed on as fuses were pulled. The key was out of the ignition during the testing, but there are circuits that work without the key (brakes, hazard, headlights, etc.). Is the belt maybe slipping even though it is within specs on tension? What about the contradiction in the Haynes testing?