1991 Ford Tempo GL won't stay started

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My Tempo won't stay started, unless it's hooked up to the mechanics computer. I'll start it and it'll either stop or run for awhile and then die. Or I'll be driving it and it'll die or I'll stop at a light and it'll die. No ryhme or reason to why it's doing it and my mechanic can't determine why yet since it stays started when he has the computer hooked up to it. He did mention it that some of the indicator lights aren't working either.