D150 wiring issues, help!

Could be failing contacts in ignition switch too. Manually operated switches are always suspect. It has a connector below the column that has been known to overheat and degrade connections also. Wait for a intermittent fault to reveal itself or start throwing parts at it? Logical diagnosis?
If everything that gets its power through the ignition switch is weak at times,,, are the always hot circuits always full on?, Headlights, brake lights, never weak? If all electrical is weak at the same times, the fault is in the root current, i.e. voltage regulator, battery connections, fusible link, bulkhead, amp gauge, weld splice.
In reference to above post, park lamp circuit feedback to a turn indicator is always a ground fault at that right or left front park/turn socket. It can be the bulb base contact to socket interior wall. More often a loose ground wire at radiator support.