Wierd F150 problem

I had an 86 F-150 that wouldn't run and sold it as is, a guy came over to buy it and tried to see if he could get it running to drive it home. We started messing with it, cranking it over, wouldn't fire at all, and then we took the plug off one of the injectors (302 engine) in order to put the test light on it, and then when we cranked it it would start right up. Then we could plug the injector back in and it would run perfect. But every time we'd shut it off, it wouldn't start again until we'd unplug that injector; and then we could plug it in while it was running and it'd run fine. We did this numerous times. Even if that injector was bad, it would be a bizarre coincidence that we happened to choose that particular one to put the test light on. Plus, why would it refuse to start, or even fire, until we'd unplug that one--and then it would start and run normal (with a steady miss of course) until we plug that ingector and then it'd run perfect? Doesn't matter to me now, the guy bought it, but I (we) thought it was strange.