The easy way would be to cut the purple wire and splice in a switch. If you open the circuit the glow plugs stay energized. If you complete the circuit, when you turn the key, the glow plugs go out.
There is a thread on how to use the temperature sensor and a relay to do this automatically. I did it and it works really well.
W124/OM603 Afterglow DIY
This works on the OM60x series of engines using the existing temp sensors. I THINK it can be done on the OM 61x series as well...
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"I have no convictions ... I blow with the wind, and the prevailing wind happens to be from Vichy"
Current
Monika '74 450 SL
BrownHilda '79 280SL
FoxyCleopatra '99 Chevy Suburban
Scarlett 2014 Jeep Cherokee
Krystal 2004 Volvo S60
Gone
'74 Jeep CJ5
'97 Jeep ZJ Laredo
Rudolf ‘86 300SDL
Bruno '81 300SD
Fritzi '84 BMW
'92 Subaru
'96 Impala SS
'71 Buick GS conv
'67 GTO conv
'63 Corvair conv
'57 Nomad
