Ok, so I had this problem for the second time now. 1989 XJ 4.0, 5sp, 242K miles. about a year and a half ago I put a high output alternator on it. About 7 months ago I was driving down the highway and the radio started acting up, then the dash went dark and the jeep quit running. There was not power at all. Couldn't even turn the e-flashers on. It sat for about 4 hours until I could come back to get it, and I got in, turned the key for giggles and it started right up as though it had no problems at all. I got on here and got to reading and found out that they have very poor grounding on the XJ's. So I added two 4-gauge ground straps to the system. Just today going to work, I noticed that my seatbelt light came on, which was followed by another total loss of electrical. I was running my headlights and a set of 55w driving lights, my heater was on full blast, and the stereo was on (plain stereo no amp, etc) This time there was enough juice to run the flashers and to get the motor to turn over once, but not enough to start it. I had a guy from work come and tow me in as I was only a couple miles away. When pulling into the parking lot I decided to put it into gear and let the clutch out to see if it would start and it fired right up with no problem. I turned it off about a minute later and then tried to turn the key over to see if it would start, and it fired right up. I'm stumped. Driving home tonight the dash gauge showed between 11-12 volts during the drive, which is a little low. Any ideas? Anyone else had a similar problem.