> Michael wrote: > The most recent acquisition (84 300D) has an glow plug relay > problem. I have replaced faulty plugs, tested wires for > continuity, and replaced the relay with two different known > good relays from operating vehicles. I cannot get the relay > to kick in. I’m getting 12 volt power to the relay and to > both sides of the fuse.
There are two power sources at the glow plug relay - the big wire going to the strip fuse and the trigger power for the relay coil. What you describe suggests you only tested the big wire - but it's not clear. There is wire red with a white stripe that is in the little connector on top of the relay and connects to terminal 15 on the relay. This should have power anytime the key is on. It's power comes from fuse #15. > The odd thing is, when I test the glow plug posts on the > relay with my analog tester it shows they each have voltage > when grounding to the engine. This voltage is present at all > times. Which post is this? The 5 terminals under the big connector on top of the relay? The big one with a nut securing the wire? I'm confused. > The weird part is that when I run a test wire from > the glow plug relay posts to engine ground I get no > reaction! No juice is flowing. Could there be a problem with > the wire(s) that connect to the ignition circuit? I'm not sure what you have done - but here is the process I would use. Using a voltmeter with one lead on ground, use the other lead on the screw on the inboard (away from the fender) end of the strip fuse. This is the "down stream" side of the fuse. If there is 12 VDC here, then turn on the key and listen/feel for the relay to click AND measure at the screw again. Expect to see about 9 VDC on the screw. If there is more than about 10 VDC, and/or the relay doesn't click, then the supply is okay, but it's not connecting to the glow plugs. If there is less than about 8 VDC I would suspect either the battery is bad or the fuse has failed. If the relay did NOT click, next measure the voltage at the terminal with the red wire at the small connector (contact #15) This should have 12 VDC anytime the key is on. If not, first check fuse #15. Then I would open the small connector and jumper from the strip fuse screw to the red wire at terminal 15. You should hear/feel the relay click. If not, the ground wire has a problem or the relay is bad. Then I would use my glow plug tester rig that uses an old +-30 amp ammeter to test each glow plug. If there is something I didn't explain well, let me know and I'll have another go at it. _______________________________________ http://www.okiebenz.com To search list archives http://www.okiebenz.com/archive/ To Unsubscribe or change delivery options go to: http://mail.okiebenz.com/mailman/listinfo/mercedes_okiebenz.com
