I'm wondering if he bumped some other wires while installing the oil sender.
Kind of sounds like a yellow wire issue. That yellow wire is power hot, with key in run and start. It supplies power to the coil, alternator (I think), various relays and some of the gauges (oil gauge for one).
I had issues with this circuit once, EcoMike lead me down the right path. The brown wire at my ignition switch connector was cooking and melting the connector, the yellow wire circuit was part of the meltdown.
Anything is possible in my experience, some things more likely than others.
I had a fuel pump circuit doing what he describes, a connector pin was making bad contact, it would heat up and the pin would flex and the pump would stop, when it cooled back down again it would work.
Double thinking this, the ignition switch seems unlikely or the fuel pump wouldn't work. More likely to be something farther down the yellow wire circuit, maybe near the ignition module and very near the oil sender, Maybe a bad splice or a wire metal fatigued under the insulation from vibration (which can be a beatch to find).
Two yellow wires going to the ignition module, the larger of the two is the power (yellow) wire. But his oil gauge problem leads me back to something under the dash, same yellow wire circuit supplies power to some of the gauges.
I must have spent a thousand hours troubleshooting Renix wiring and I'm actually pretty good at it. I learned how to troubleshoot wiring on M-60 main battle tanks (miles of wire) and UH 1 helicopters. I find Renix to be more difficult than tanks
not as bad as Helicopters. About the time you think you have seen it all, something new pops up.
