'83 300D Turbo - No glow plug indicator light, excessive crank, hard start only when cold. Tested relay plug, found 2 glowplugs registering 2.3 and 11 ohms (0 for other 3). Can 1 or 2 weak plugs cause the whole curcuit to be non-functional? The plugs and relay were all changed 30K miles ago (Bosch). Are the plugs numbered 1 through 5 from front of engine to back? Should I replace all 5 again? Should I replace with BERU? Thanks!