95 Tacoma Manual 4cyl 2.7 4x4. No problems or even indications prior to this. No recent work done. I changed the tape deck to a CD player 6 years ago, everything else is stock (no new speakers, lights, anything).
This morning it was about 20 degrees. Truck started no problem no hesitation. As I started to drive off it dies. The type where the RPM needle swings wildly back and forth and warning lights come one. I try re-starting it starts, 2 seconds dies. I turn my head lights off and restart it, starts right up and idles normally. I role the light switch to turn on the parking lights and the engine starts working a little harder, (was sitting at 1.5 RPM now bouncing between 1.5 and 2). Role the switch to lights on and the engine dies.
With the engine off the lights work (slightly dimmer than with the engine on but not much). Then I turn off the lights and start the truck and let the engine idle until the temperature gauge starts moving. It's cold so I try turning on the heater. Setting the fan at 2 gives me that 1.5 to 2 RPM bounce, clicking it to 4 (or 3+parking lights) kills the engine. I experiment on and off with various things for nearly 30 minutes (the engine on and running most of this time) and then she's fine.
Drive the 3 miles to the gym with lights on when I get there I figure I'll test it so with lights on I flip the fan to full blast and turn on the radio. No troubles at all. 1 hour later as I'm leaving everything works perfect like nothing was ever wrong.
Truck has plenty of battery power to start the car or run the headlights but doing both kills it. Or turning the fan to HI with the engine running will kill it.
So I'm thinking it's not the battery because the truck started over and over with no problem. Once it's running the alternator starts powering everything but it's not putting out enough power to keep the engine firing and the lights on...but only while it's cold? What's going on? And what do I need to fix?