D
Dunkuk
Guest
This is my first post on here but I thought I'ld make it a useful one. This shows how to fix your glow plug relay.
The relay is situated in front of the battery and is easy to access, it has 1 thick 12v lead going to it held on by a nut (10mm I think) and one big 4 way connector taking the 12v off to the plugs, and one little connector taking the control signal from the cars computer.
My glow plug light was on when I bought the car. Taking the plug off the front of the glow plug relay revealed 4 connectors, one going to each glow plug. By measuring the resistance from each of these 4 connectors to earth (cylinder head) I found that all measured around 1-2 ohms, which is what they should be.
I then connected a headlamp bulb to each of the outputs of the relay in turn, the 4 male spade connector parts within the large connector. So one side of the bulb to the relay, the other to earth. Then turning the ignition on the bulb lit up (taking the place of the glow plug). 3 of the pins made the bulb light, one did not. So the relay must be faulty I thought.
Looking at replacements, a 2nd hand one on ebay costs about £30, a new one from GSF car parts costs £80. Quite a lot, so I thought I would try repairing the relay.
The relay is glued shut with a hard black material. Too hard to cut with a knife. I drilled this out with a pillar drill and a 2.5mm bit working my way all the way round. I then joined the holes up with a stanley knife and a small chisel for the harder to cut bits. I then prised it apart with a chisel.
This revealed that a "fusable link" had blown, basically a fuse made of a thin bit of metal. Photo 1.
I soldered on a 30amp blade fuse (the glow plugs take 11A to 16A on my car so 30A should be plenty). Photo 2.
At this point I tested it in the car before I glued it back together, and it worked fine.
I removed any small bits of plastic left over from cutting to make sure they don't jam up the relay, then glued it all back together with Gorilla glue (foaming wood glue), although I would imagine hot melt glue, expoxy or silicon sealant would work. Just be careful not to get any glue on the relay.
Once dried I put it back in the car and it all works fine and the relay light is off.
I hope this is helpful to someone.
By the way my local specialist garage would have replaced the glow plug first (as the computer cant tell the difference between a blown fuse and a blown glow plug, then replaced the relay, probably looking at £200 or so of parts + labour with genuine MB parts.)
The relay is situated in front of the battery and is easy to access, it has 1 thick 12v lead going to it held on by a nut (10mm I think) and one big 4 way connector taking the 12v off to the plugs, and one little connector taking the control signal from the cars computer.
My glow plug light was on when I bought the car. Taking the plug off the front of the glow plug relay revealed 4 connectors, one going to each glow plug. By measuring the resistance from each of these 4 connectors to earth (cylinder head) I found that all measured around 1-2 ohms, which is what they should be.
I then connected a headlamp bulb to each of the outputs of the relay in turn, the 4 male spade connector parts within the large connector. So one side of the bulb to the relay, the other to earth. Then turning the ignition on the bulb lit up (taking the place of the glow plug). 3 of the pins made the bulb light, one did not. So the relay must be faulty I thought.
Looking at replacements, a 2nd hand one on ebay costs about £30, a new one from GSF car parts costs £80. Quite a lot, so I thought I would try repairing the relay.
The relay is glued shut with a hard black material. Too hard to cut with a knife. I drilled this out with a pillar drill and a 2.5mm bit working my way all the way round. I then joined the holes up with a stanley knife and a small chisel for the harder to cut bits. I then prised it apart with a chisel.
This revealed that a "fusable link" had blown, basically a fuse made of a thin bit of metal. Photo 1.
I soldered on a 30amp blade fuse (the glow plugs take 11A to 16A on my car so 30A should be plenty). Photo 2.
At this point I tested it in the car before I glued it back together, and it worked fine.
I removed any small bits of plastic left over from cutting to make sure they don't jam up the relay, then glued it all back together with Gorilla glue (foaming wood glue), although I would imagine hot melt glue, expoxy or silicon sealant would work. Just be careful not to get any glue on the relay.
Once dried I put it back in the car and it all works fine and the relay light is off.
I hope this is helpful to someone.
By the way my local specialist garage would have replaced the glow plug first (as the computer cant tell the difference between a blown fuse and a blown glow plug, then replaced the relay, probably looking at £200 or so of parts + labour with genuine MB parts.)
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