Fuse blowing wiper motor

[panda911]

Hi.
I have single speed self park WW motor on my 1071, it is May 66 manufacture.
It works if you do not connect earth wire.
Connecting earth wire blows fuse
Earth wire is indeed neg battery.
Armature looks good as does commutator, brushes good.
Could there be a shorted turn on the feild coil.
Any ideas please.
BR
P

[Andrew1967]

Should there be an earth wire ? I know there’s a terminal on one of the casing screws but not sure it’s used.

Will check my mk2 when I get home.

[panda911]

Thank you Andrew.

[mk1]

Wiper motor should have 2 connections, one from a switched live (Black Green) one to earth, usually on the back of the speedo. Both are insulated wires that connect to terminals within the wiper motor unit.

If the motor is working without the black wire attached, the motor must be earthing somewhere other than where it should be. If connecting the earth blows a fuse then it is likely the body is live. To start with, check for continuity between the wiper motor body & the car body, if there is continuity then there is probably a short within the unit. This needs bottoming out urgently.

It is rare that issues like this don't fry wiring looms. You have been VERY lucky so far.

M

[Andrew1967]

I’d agree with Mark.

Just checked my Mk2 and there are three wires .. two onto the main terminals as per the two wire Mk1 type and one black to a terminal on the motor body main screw. I assume the third black earth wire is for the self parking that mk2’s have

Mk1’s just have the two wires directly onto the main terminals as Mark says and I eluded to originally .

A photo may help us solve your problem if it still persists.

[Old English White]

Possibly a side issue, but I didn't think that any Mk1 Minis had self park wiper motors??

[Andrew1967]

No, pretty sure not Richard, mention of self parking was purely due to fact that self parking motors have seperate earth wire, which is presumably what the OP was trying to fit. Maybe confusing issue now.

Mk1's have only two wires to the main spade terminals on the motor.

[Peter Laidler]

No doubt about it....... Self park motor, it is a defective limit switch. The white plastic plug-in switch is a heat sealed unit and unless it is tested in-situ or within a slave wiring harness, there's no (?) other way it can be tested. Another thing to remember is that a blown fuse indicates a wiring overlioad..... in this case by the defective limit switch.

I could be wrong of course, as wifey tells me every day

Added a bit later..... Just been told that the limit switch was always susceptible to water ingress - and subsequent internal corrosion - because of its upright location at the point where water from the bonnet can drip down onto/into the wiring entry point. Seal the opening with mastic.

[Andrew1967]

Interestingly and annoyingly I have a similar issue with one of my self parking DR3A motors.

So testing it on my Mk2 Cooper, the motor works 'non self parking' if the earth wire isn't connected but when the earth wire is connected the motor works continuously with the ignition on with the wiper switch either on or off and eventually blows the fuse.

Taken it apart and can see no difference to the other self parking motor I've just rebuilt that works as it should !

Any ideas