continuity issue full rewire

Ok so I had some time this week to work on my electrical system again... "THE LOOP" as I have come to call it, is present not only in the from marker / turn signal lights, but in head lights as well. "THE LOOP" is eliminated as soon as the bulb is removed from the circuit. To save those of you just seeing this from reading the whole thing the problem is that my turn signal indicators both light when one turn signal or the other is activated (or the parking lights are on), and as I recently found the high beam indicator is activated when either the old beams or the high beams are connected. BUT AS I MENTIONED ABOVE THE PROBLEM IS RESOLVED BY REMOVING THE BULB. My theory as I mentioned above is that power is passing the through one filament, to the bulbs common ground, back throughout other filament in the bulb and traveling backwards up the that supply line. In the case of turn/parking lights this means the parking light filament acts and a path of travel between the 2 turn signal circuits. If I'm right the solution is to install diodes on each power line. But I don't trust my own, informal, knowledge base. PLEASE ADVISE

What you are describing is a broken or insufficient ground. If the ground were intact, then as I wrote earlier, it is impossible for current to travel from +ve to ground and then "back up" another path to +ve. However in the case of indicators/flashers, it is probably a case of bridging (interconnection) between the RH & LH sides. All bulbs must be removed for a continuity test. A DMM's continuity test is only good for testing wire/circuit connectivity between 2 points - eg, RH output of flasher switch & RH +ve of the RH flasher bulbs versus RH out & LH bulbs or GND etc, and bulb GND to GND. With bulbs etc in the circuit, measuring continuity between two +12V points (with the +12V source removed of course!!) does not mean there is a fault. EG find a working brake and tail light but ensure both are of (unpowered)... Measure the the continuity between the +12V of each bulb. There will be continuity yet the 2 circuits work fine. They are not "shorted" together.