300cd glow plug & relay Test - Mercedes-Benz Forum

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post #1 of 1 (permalink) Old 02-08-2012, 07:06 AM Thread Starter
BenzWorld Newbie
Date registered: Feb 2012
Vehicle: 1978 300CD 123 body early vin number in the 2,000
Location: Nashville, TN
Posts: 4
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(Thread Starter)
300cd glow plug & relay Test

I have been testing my 1978 Mercedes 300cd glow plug circuit today. Sometime my glow light will work and sometimes it will not which causes hard starting in cold weather. I have the “loop” glow plugs removed and have them hooked together in series on my work bench. I connected them to my battery using jumper cables and they all glowed very cherry red……so I know they are good. I connect my postive test on my multi tester lead to the power wire going to number 5 cycl (AFTER the flat fuse mounted on the firewall) I then connected the negative from battery to the glow plug ground (the flat cable) that was connected to the number 1 cyl. I was surprised that my test meter showed 6.6 volts with the key off and out of the ignition. I turn the key to glow position and got 9.9 vols. Do you know if I should have 6.6 volts with the key out? Is 9.9 volts ok with the ignition key in glow position? If 9.9 Volts is Ok does this mean the relay is ok. I have an earlier vin number which has the relay mounted under the dash.
I am considering converting to the pencil type glow plugs just to get faster and hotter warm up and I wanted to find out if I my relay is good before I convert to the pencil type wired in parallel and not serial. If relay is good can I use the same relay?

Thank you for your help
Bfowler71 is offline  
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