Emergency start for diesel with suspect glow plug relay failure, connect a `heavier` wire ( 120/030) wire between battery positive and the common positive rail of glow plug input feed at block for several seconds, crank engine, if starts then glow plugs ok, if no start glow plugs not ok. remember only needs one glowplug to fail to give bAD STARTING. ALSO AS PREV AVOID LEAVING WIRE CONNECTED FOR MORE THAN A FEW SECONDS OTHERWISE COULD WELL DAMAGE `GOOD` GLOW PLUGS! remember the wire must only be connected for seconds at a time and not in pace once stasrted or on leaving your vehicle (ALSO FOR OTHERS SOME PLUGS WORK ON DIFFERENT VOLTAGES , BEWARE AND TAKE CARE WITH/OF THIS METHOD IF YOUR PLUG VOLTAGE IS LOW OPERATING).
STEV AL
February 2006