I've got a 79 Honda cm400t. Had it out the other day and it was doing fine when the oil pressure light came on. Pulled over and checked the oil and it was full. Drove it a few miles home and the bike sounded and ran fine. Changed the oil and filter today, but the light still stays on. I suppose I'll pull the side cover when the weather permits (too chilly right now) but don't quite know what to do after that. If I revve the engine, the light goes out, and when the filter was off, oil would pour out when I turned the engine over, so the pump is working a bit. Could be the oil pressure sending unit is bad; I bought it online about a year ago. Pump could be bad, but I don't know how to tell. Any suggestions? I've split the engine case in the past and don't want to do that again unless I have to do so. Oh, I did push the pressure relief valve when changing the oil filter and it seems to work, though I have no way of know if the spring is weak or it is not sealing.