2 replies to this topic

[dschwartz1957]

Last season I had an electrical problem with '68 Mini where turning on the wipers while the engine was running caused the engine to die. The wipers worked fine when the engine was off, and the engine ran fine while the wipers were off. I started trouble shooting the problem in the fall by running a new wire directly from the fuse box to the coil and replacing the coil. Neither of which made a difference.

Over the winter I removed the wiper motor from the car and gave it a thorough cleaning / de-greasing in the warmth of my basement workshop. Now that spring is finally here I started looking for wiring issues in the car. Initially I didn't find anything but a little bit of insulation missing at the base of a connector on a 12 volt lead at the wiper motor. I was planning to cut off the old connector and crimp on a new one. However, when I removed the electrical tape from several inches of the wiring harness I found melted insulation and bare copper wire. This continued over most of the wire all the way to the dashboard switch. Then I traced a different lead from the dash switch that disappeared into the wiring harness and found more melted insulation and bare copper. Finally I traced the black wire from the switch and found an inch of melted insulation near the bullet connector where it plugged into the harness.

 

The wiper rack is difficult to move by hand and needs a good clean, lube and adjustment. I believe the wiper motor was drawing too many amps causing the wires to heat up and melt the insulation. The good news is I did not find any other damaged wires adjacent to the wiper wiring. I had to remove a lot of electrical and friction tape from the harness to be sure, but this was time well spent.

 

Like all Mk1 and Mk2 Minis, my car only has two circuits each protected by a 35 amp fuse. I plan to install a separate in-line fuse on the 12v lead to the wiper motor. What amp fuse should I use to protect against this problem recurring?

Thanks,

David Schwartz
 

[KernowCooper]

The early Lucas wiper motors were 14w as the motor only draws a low current of approx 1.5amps and gets its power from the gearing,so in your case as you found out a 35amp fuse does little to protect the wiring if it shorts out, a 10amp inline fuse would cover the initial start current and protect the wiring which the new wire you fitted I hope has a higher rating than the 10amp fuse, if you fit a 5amp fuse it will then likely blow on initial load when the wiper are switched on.

You have to watch out though as the stall current on these motors raises to 15amps if stopped and loaded like if the wipers are stuck to the screen in winter with ice

 

6lbs of pull on the rack and wheel boxes is the maximum pull by the way with a balance weight connected to the end of the drive cable

Edited by KernowCooper, 18 April 2015 - 08:50 PM.

[dschwartz1957]

I plan to clean and lube the wiper rack (linkage to the arms) to fix the binding before trying to operate the wipers and the engine simultaneously. A 10 or 15 amp fuse will be safer than the 35 amp fuse that currently protects the entire circuit.

 

My car was converted to negative ground long before I bought it. The wiper motor is single speed which is appropriate for a '68 Mk2, but is round body which came later. It is possible the dash switch and wiper motor were wired incorrectly, since it is a single speed motor which only has two brushes, yet there were three wires running to the motor (12v, ground, and dash switch), and three wires running to the dash switch (12v, ground, wiper motor). The wiring does not match any of the Mini shop manuals.

 

The Mini shop manuals show a 12v wire going directly to the motor, and wires from the two speed dash switch running to a variety of terminals on the self park switch. I am going to bypass the self park switch on the motor which hasn't worked since I bought the car, and install an inline fuse in the 12v line at the wiper motor. Since the car has a single speed motor and single speed dash switch, I will run a single ground (earth) wire from the dash switch to the second terminal on the motor. Someone used a combination of 16 gauge and 18 gauge wires, and connected mismatched gauge wires using the original style bullet connectors. I am rewiring with all 16 gauge.

 

The numbers '3 71' on the motor may be the manufacture date, so this motor is not original to the car. The removable motor panel has the following printed on it:

75738F
Park <--
14W
12V    3  71
54071664F

 

I wonder if it would run at two speeds if I install the 3 brush plate. I would need a two speed dash switch, plus a new self park switch. Those parts are surprisingly expensive.
 

For others trouble shooting gremlins, there is good Lucas electrical info on an MG website:

http://www.mgb-stuff...htm#wschematics
 

David