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MG Midget and Sprite Technical - Blowing Fuse.

Just about rewired the 72 midget.
Problem is : The wipers work for about 10-15 seconds then pop the fuse .
Anyone any ideas ?

G Bewick

Fuses melt rather than blow (if they melt instantly if you say touch live wires, water spill, etc.)

So the wipers could run for a short while before the fuse fully overheats.

As for the cause you probably need to give more info on the wiring you've done and need one of the contributors with more knowledge of electrics.

10-15 seconds sounds a long time, how many sweeps of the arms were there.
Nigel Atkins

Its a new loom and everything is as the wiring diagram.
No wipers attached and as said, the motor wil run for a short while before the fuse goes.
G Bewick

Sounds like the motor is struggling to work and drawing too much current.

Does the motor sound as though it is struggling?

Were the wipers OK before the rewire, or has the car been unused for some time?

Possibly dry/hard grease in the rack mechanism.

Have you tried running the wipers with the arms removed?

Do you have a suitable ammeter that you could put in place of the fuse to see how much current is being drawn?
Dave O'Neill 2

might sound a silly and obvious question but - what type and size of fuse was used, an original 17 continuous 35 blow or different?
Nigel Atkins

if the wiper blades are not attached would the arms make much odds as presumably the arms would be lifted off the screen (or there isn't a screen) so no real friction resistance there.
Nigel Atkins

I'm with Dave. Suggest you have a good feel of the wiper motor immediately after the fuse fails. It shouldn't get warm in 10 to 15 seconds - if it's warm you've found the culprit.

Sorry I didn't mean to sound as if I was disagreeing, I'm with you both which is why I asked how many sweeps and also to draw out a bit more info, I was just curious about Dave's question about removing the arms (unless Dave missed Gary's second post and the bit about no wipers attached).

No mention of rack noise or resistance so motor is a good choice, I was just initially cautious because of the just rewired without further info.
Nigel Atkins

Hmm... Don't see a disagreement Nigel. Seems to me that concensus suspects the motor. I certainly think it's the likely explanation, although it's possible for high circuit resistance to lie elsewhere. (Wiring/switch blah blah).
But my money is on the motor still. Good news is they're not usually hard to fix.

Not even a gentle one

- sorry but I loved that remark. :)
Nigel Atkins

Nigel, you are correct.

The OP's second post appeared 43 seconds before mine and, as it took me considerably longer to type it, I hadn't seen the part about the wipers not being attached.
Dave O'Neill 2

Dave I do that all the time. Sometimes, for various reasons, I take so long to type a post that not just one but two or three other posts go up in the meantime and I struggle to keep a pace - not that anyone would notice of course. :)
Nigel Atkins

Don't forget that because the wiper motor is connected on the ignition side, other things are powered up when the wipers are powered. Could it be combination of things?
Graeme Williams

Yeap it could, Dave has suggested getting a meter out, on the other side Gary has put that it's a new loom wired as diagram.
Nigel Atkins

Disconnect the spiral rack from the motor. Or rather quicker and easier, undo the acorn nut that holds the rack outer to the end of the motor gearbox. Then try the motor.

Either of these will take the load of operating the rack itself off the motor as an elimination test.

Had a similar issue when reinstating the original wiper motor & mechanism after a couple of decades :( of unuse. They wiped very slowly with the motor struggling to power them - as Dave says, packed, hard, dried out grease was the culprit.
A new rack, grease and turning the wheelboxes through 180 degrees (to use the unused portion of the cog) had it working as well as new.
Jeremy MkIII

I have found several wiper motors to have hard packed grease. The factory used something similar to wheel bearing grease. It hardens over time. I have rebuilt mine with a lighter grade of grease available from John Deere farm tractor dealers. For the amount you may use your wipers now, I think a white lithium grease would work in the gear box and the wheel boxes.
J Bubela

Have you fixed it?
we need to know!
Jeremy MkIII

Removed the spiral cable from the tube and found chunks of hardened black grease.
Cleaned the tube, spiral cable and spindles and its working sweet :)

Thanks gents.
G Bewick

Many repairs and much servicing and maintenance are a matter of cleaning and lubricating, I'd suggest continuing the cleaning and lubricating to the motor and checking all the electric wires and connections are clean, secure and protected, including the switch.

Only last night I tried to get the rocker wiper switch out of the dash and in trying to expose the tags that hold the switch to the dash I twisted off the back part of the switch by mistake and the back came off and innards fell to the floor, so I ended up even cleaning the inside of the switch.
Nigel Atkins

This thread was discussed between 15/07/2017 and 20/07/2017

MG Midget and Sprite Technical index

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