1994 Lexus GS 300

Electrical problem
1994 Lexus GS 300 6 cyl Two Wheel Drive Automatic 150000 miles

There appears to be a short somewhere in the electrical, and I'm hoping for some suggestions to find it.

- The first symptom was turning the ignition would sometimes not start the car. Trying again, the car would start fine.
- Next the battery light on the dashboard started coming on. That happened to coincide with cold weather, so I thought at the time it was related to that.
- Then one morning turning on the ignition, the car started fine and the engine was running, but the dash lights were very dim and the car wouldn't shift into gear. I measured directly at the battery terminals and saw 5V (with the engine running). Half hour later I tried the car again and it ran normally.
- A few days later, after the car had gone about 40 miles, the radio suddenly started making a loud buzzing at maybe around 100Hz, then dropped out entirely after about 10 seconds. As I continued down the road, the dash lights continued to dim and I started loosing electrical systems one after another. I tried shutting off heaters and whatever else, but saw no effect. The transmission eventually stopped shifting reliability, and finally the car stalled after several miles as I tried to make it up a steep hill. Up to that point, the engine was running fine. Immediately trying to restart the car, it just made a clicking sound like a dead battery. But after about 15 mins I tried again, and the car started normally and ran fine.

The battery is new and usually has a healthy 12.5V charge. I'm guessing the problem is an intermittent short somewhere that is enough to drag the voltage down, but not enough to blow a fuse. It's tough to diagnose, because the problem occurs randomly. Next time this happens, I was planning to pull over and just start pulling fuses live until the headlights spring back to normal glow. Not ideal, but I'm at a loss. Any ideas would be greatly appreciately.
February 18, 2010.

Much simpler than all this. The engine block leaked oil into the alternator and caused it to fail.

Feb 25, 2010.