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Old 02-14-2013, 10:53 PM
1987 300TD wagon, 225k
 
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1987 300td 80amp fuse being shredded - help

Just had a starter motor and oil pressure sender unit put in. Now the glow plug relay 80 amp fuse link gets blown every time I turn on the car. Gone through three already. Have a wire in there now to start the car. Have a feeling something's no longer grounded properly? Any one ever have this issue? Any ideas appreciated. Would love to get the proper fuse back in there.

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Old 02-14-2013, 11:06 PM
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Quote:
Originally Posted by brooklyn View Post
Just had a starter motor and oil pressure sender unit put in. Now the glow plug relay 80 amp fuse link gets blown every time I turn on the car. Gone through three already. Have a wire in there now to start the car. Have a feeling something's no longer grounded properly? Any one ever have this issue? Any ideas appreciated. Would love to get the proper fuse back in there.
Not sure but I'd recommend that you remove the piece of wire before you have a fire. If the 80 amp fuse blows right away you must have a serious short circuit. Check the glow plug wires to make sure one is not pinched/shorted and try disconnecting glow plugs to see if the short goes away, maybe one of them is shorted. Check the ends where the wires screw on to the glow plugs to be sure the metal eye is not grounding out on anything.
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Old 02-15-2013, 09:01 AM
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I know it's tight visibility in there, but you have to follow the glow plug harness from the relay to each and every plug and find the one that the starter mechanic pinched.
one is grounded, and killing the plug. using a wire will cause a fire and destroy your car... don't do it.
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Old 02-15-2013, 09:21 AM
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Good thinking in the last post and probably very accurate in your case.


Another reason for not using a wire as a as a temporary fuse is you might flow more current through the glow plug relays contacts than they can tollerate. The weakest link in the glow plug circuit is going to suffer the most stress.

A dead shorted glow plug. That is one showing zero resistance is a not unknown cause as well as a feeder wire to a glow plug being shorted out somewhere. Keep this in mind for future issues if any.
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Old 02-15-2013, 09:58 AM
1987 300TD wagon, 225k
 
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80 amp fuse

thanks guys, will take the wire out right away and start testing the plugs/wires to see what I find.
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Old 02-15-2013, 12:38 PM
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If somewhere on the Wiring Harness there is a Steel Bracket with a Rubber sleeve or coating on it the rubber typically deteriorates and can rub through the Insulation on the Wire.

Someone in another thread mentioned that if you disconnect the Connector going to the Glow Plugs themselves and you try to Preglow and the Fues Burns you have an issue in your Relay.
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Old 02-15-2013, 01:27 PM
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Ohm meter on each connection in the plug at the relay should find it. But I don't *think* the glow plug wires are anywhere near starter so i'm not sure what that person did when replacing starter. Maybe just a coincidence.
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Old 02-15-2013, 09:48 PM
1987 300TD wagon, 225k
 
Join Date: Nov 2011
Location: brooklyn, NY
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Update - buy 80 amp fusible link from dealer!

Before I undertook looking into the glow plugs and wiring, I bought a handful of 80amp fuse strips from the dealer. Hard to do because they're $5 a piece compared to 50 cents online (the three I blew bought online). Wanted it done soon because of the fire issue everyone's mentioned, stuck it in, and voila. So far no problems. The dealer fuse seemed quite a bit more robust, doesn't bend as easily, etc. I guess there are some things that have an economy to the premium, especially since this can be such a fail part that can strand you anytime.

Anyway, thanks again all for your help.
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Old 02-15-2013, 11:19 PM
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I think there are two different amperage rating fuse links for the glow circuits. Some cars take the lighter and some the heavier one. Fifty and eighty amp varients come to mind but not in anyway sure.
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Old 02-16-2013, 07:05 AM
1987 300TD wagon, 225k
 
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Location: brooklyn, NY
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50 vs 80 amp

You're right, the same strip fuse comes in both 50 and 80 amp. The ones I got that kept blowing had 80 A printed on them so I assumed they were right, though very possible they were a misprinted strip or some such error. A noticeable difference in thickness between the ones I got from the dealer. I think the 50's are for a heater maybe? Wouldn't be a big deal except that little fuse had the unfortunate side effect of disabling the car. Good to point out though that there ate two different amperages out there. Thanks.
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Old 02-16-2013, 09:23 AM
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Quote:
Originally Posted by brooklyn View Post
You're right, the same strip fuse comes in both 50 and 80 amp. The ones I got that kept blowing had 80 A printed on them so I assumed they were right, though very possible they were a misprinted strip or some such error. A noticeable difference in thickness between the ones I got from the dealer. I think the 50's are for a heater maybe? Wouldn't be a big deal except that little fuse had the unfortunate side effect of disabling the car. Good to point out though that there ate two different amperages out there. Thanks.
I believe some of the mercedes glow plug systems use the lighter fuse. It really sounds like that is what you got from ebay no matter what the markings on them where.

Heater fuses and their holders are a problem as well on some of their cars. But they are not fifty amps. The cure is to add an external fuse and holder for the heater circuit. Seems the fuse contacts in the fuse panel are not up to the job.

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