Oil temperature sensor ground - Titan engines
Very similar to this thread, related to single wire temperature sensor grounding on a Titan engine with oil filter angle mount (Mine is a 340, but I think most other models have this, or similar filter adapter).
When I wired my Dynon EFIS system, all was well except for no oil temperature reading, with the system saying no signal at all. We checked and rechecked the wiring; all was good. Decided the sensor must be bad, but it checked ok with a meter (reading from body to center electrode). Engine grounds looked good and everything else was working. Finally, tested from the sensor body to several ground points and there was no connection -- well, several million ohms.
Cause: The temperature sensor body is threaded into a nice angled oil filter adapter. The oil filter angle adapter that Continental/Titan uses is essentially an extension on the accessory case, solidly bolted to it with 4 through bolts. Of course, there is a gasket at the base, and powder coat on the outside. The 4 through bolts are fitted with washers under the heads that don't necessary scratch through the powder coat, resulting in an effectively insulated oil filter adapter, and thus no ground for the oil temperature sensor. After tracing wires (and maybe cussing a bit) for the better part of a day, it simply took a little scratching paint under the head of a bolt. (well, 2 for safety)
If you have this issue with a Titan, give that a look. I suppose it applies to other situations where you would think a component JUST HAS to be grounded to the engine (but isn't)
Ted