It is running. It runs until it depletes the battery, and while it's running, the volts jump around on the gauge, so the alternator isn't working or something.
This does not make sense at all In your previous post you said "runs momentarily."
A car with a good and with a charged battery (old, non EFI) should run HOURS on a battery, and I have done it. If you are running down the battery just running the car in the garage, either some serious wiring problems or junk battery. I'll say it again........you need to fix the engine problem then worry about the alternator
There is one other possibility, and that is you have a terrible situation with your bulkhead connector, as an example. Try "hot wiring" the ignition and see if that improves the engine run situation. That is, jumper 12V from battery direct to the "key side" of the coil ballast, or the "key side" of whatever other system you are using.
What experience do you have? You fairly checked out on wiring, do you have a service manual, and what have you done to try and torubleshoot the overall problem of the engine run proboem or the alternator problem?
