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Old 09-06-2006, 07:25 PM
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Posts: 47
79 300SD unsolved problem

I have a 1979 300 sd (116). The brushes on the blower motor went bad. I put in a new motor. Before the brushes went bad it never blew a fuse

It will now run for a few hours and then blow #3 fuse.

I have done the following:

1) cleaned the fuse holder contacts
2) put in new mercedes fuses
3) disconnected the aux water pump
4) cleaned the ground connection
5) took the new fan out and re-installed it.

My #3 fuse is a 16 amp fuse....that is what the paper on the top of the fuse box says it should be. An old thread stated that his 79 300sd had a 25 amp fuse in #3. Am I putting in the wrong amp fuse??????What else could be causing this.

Thanks for your help


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Old 09-07-2006, 12:39 AM
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does the new motor spin nice and free?
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Old 09-07-2006, 01:18 AM
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Location: Nova Scotia, Canada.
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I would first of all increase the fuse to 20 amps to see if it holds. If there is a major short occuring it will still give you enough protection. If it holds you are away to the races. Since you saw a refference to a 25 amp in that curcuit there may have been a revision of the blower motor during the production run at some point to make it a little stronger. I would do a little research on that. Were the part numbers on the old and new motors the same for example? your new motor could also have a defect as well. Or a bare wire might be intermittently shorting in the circuit for example.

Last edited by barry123400; 09-07-2006 at 01:23 AM.
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Old 09-07-2006, 07:23 AM
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Join Date: Oct 2003
Posts: 47
Yes the new motor did turn freely.

I was thinking that they may have changed the motor's specs. I read in an old thread that the motor will draw up to 18 amps. It seems that a 16 amp would not last.....

I will do some more research

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Old 09-07-2006, 10:29 AM
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Location: Mount Holly, NC
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My 82 SD has a 25 amp fuse on the blower.

I know the 126's are different than yours, but it stands to reason that the blowers would need similar amounts of power.

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