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MG MGB Technical - 67 BGT 2 Speed Wiper Wiring?

My 67 BGT has a 12W round body 2 speed wiper motor original to the car. Face is stamped 12W DA. 12V 2-67, 54071398F, and 75580F PARK ->

My new wiring harness has the roadster 3 wire connections; black, green, black/green. My motor has those wires with the EXTRA red/green wire as the 4th wire. It is long enough to go directly to the dash switch but I can not determine how to connect it to the double throw switch. I have 4 terminals available but I can't determine what happens in the wiper motor with this wiring. I have not found any wiring diagram that specifically shows how the motor or switch operates.

I have found a few references to the 67 GT (only) having this 2 speed round body with the extra wire but no help wiring it to the switch. I keep blowing the 35A fuse even when i get it to run a bit in both speeds, so I know I must be crossing up. Since it is a motor and not a light, it does things more complicated than my simple understanding of electric magic. Any help? Thanks Ralph
R Stegs

OK, dat's da odd one!
Assuming your car is pre 139824, and hoping you have the correct original switch:
(later cars have different wires: B, G, ULG, NLG, RLG)
(There seems to be a discrepancy in the WSM, showing two BG wires and no RG. Also. the switch diagram seems to be incorrect, I hope the terminal numbers are right!)
This system is power from fusebox to motor terminal 1 = G; everything works by switching to ground.
The park switch grounds through B, motor terminal 4.
(this is apparently wrongly identified as BG off the motor, changing to B midwire)
The main switch grounds through B off terminal 4.
BG from motor terminal 2 goes to switch terminal 2.
LG goes from motor terminal 5 to switch terminal 3. This is evidently your RG.
No wire on switch terminal 1; it is internally bridged to terminal 3 (I think).

This motor has 4 terminals, numbered 1, 2, 4, 5; Later cars actually have 5 terminals on the motor, and all switches other than this one have 8 terminal positions on the switch, although they don't all actually have terminals. To make things even more fun, it is possible that the switch has been changed for a different 8 terminal one, of which there are numerous variants. I once wired up a midget that I had converted to two speeds using some headlight switch, MGB I think.

FR Millmore

The 67 GT was a cross-over model. The schematics indicate three different kinds of motors and wiring with two different parking methods, but there seems to be a fourth one in the field. There is also a sub-harness for one of the options to connect the motor to the earlier harness and later dash switch. More info here
PaulH Solihull

Gentlemen, thanks very much. Of course I am not lucky enough to have the original switch so I have one of these new three position Lucas. I also have a new similar switch with 6 spades.

Paul's reference found this quote which seems to be my circumstance with the wire colors but this is ONLY A SINGLE SPEED (according to the text): 67 GTs seem to have had the round motor with the later parking system but they were only single-speed. The wire colours and functions are as follows (confirmed by Glenn G, Texas autumn 2005):

Black - ground for motor and parking switch
Red/Light-green - run 12v supplied from manual switch
Black/green - park, connected to red/light-green by switch. Carries 12v when wipers are not parked, ground when they are in the park position
Green - 12v supply to motor parking switch and manual switch

So now I am wondering if it is possible that I was creating the second speed before blowing the fuse as I attempted to wire? The initial speed was simply a slight pause between cycles, the second speed was no pause..... sure seemed to create two speeds though. OR perhaps the wiring would be the same for one vs two?

All of this really comes down to me trying to wire this switch.. I used my continuity tester to determine which terminals connect when operating the switch and want to transfer that to what the motor needs. So a good start is FRM's info on the grounding of the sytem to operate. Now I have to match that up to what this switch does. Normally open etc...

R Stegs

Hi Ralph.

I have one of the single speed round ones from my 67 GT. It is a very late one. It has the internal "fingers on a brass ring" parking/power system. I was able to convert it to a later model 2 speed with the external parking system.
Bruce Cunha

Scratch my comments, as you seem to have a single speed motor. I think my remarks are for the square two speed, but the WSM doesn't tell you that! You should be able to figure it out from Paul's info. All most confusing, but then it was last time we went through this.

FR Millmore

It sounds to me like one of your speeds is in fact the park switch shorting out the power momentarily as it passes through the park position. There should be no pause, the motor should run constantly, in either speed on a two-speed system. In theory this should stop the motor dead and blow the fuse instantly, but when you start adding in practical factors such as resistance in the wiring back to the switch and fuse, and in the park switch, anything could happen. The USP of the later parking system is that instead of just disconnecting power from the motor, and allowing it to spin down to a halt, which gives a variable park position for the blades depending on how wet i.e. lubricated the glass is, it shorts out the motor as well as disconnecting the power. When a motor is spinning under its own momentum, i.e. immediately power has been disconnected, it is a generator. Short out the output of that generator, and it puts a massive current load on it, which stops it pretty-well instantly. On a wiper motor that gives a consistent park position for the blades.

As a relatively generic switch you will have to draw up a chart of which terminal numbers are connected together in each of the three positions, then work out which terminals you need to perform the run and park functions. And that will depend on whether you have a one speed or a two speed motor, and which park system it has. The early system uses 12v at the motor, an earth from the switch to run, and an earth at the motor to park. The later is quite different. There *should* be enough info in that link to suss that out, and how to wire it.
PaulH Solihull

Okay that is what I suspected once the motor paused briefly before speeding up a bit.

From Paul's site I found this info on the actual sub harness that I have with this motor. It is this harness that I need to use with the roadster harness.......

Update May 2008: Niels Hansen has contacted me with information about an adapter harness that allows the single speed GT motor with the later parking system to work using the standard roadster harness, and also a correction to my schematics. Click the icon above for the schematics and here for a picture of the sub-harness.

Black - ground for motor and parking switch
Red/Light-green - run 12v supplied from manual switch
Black/green - park, connected to red/light-green by switch. Carries 12v when wipers are not parked, ground when they are in the park position
Green - 12v supply to motor parking switch and manual switch

The two wires in the new harness (roadster) for the wiper switch are the Black/Green and Black. They drop out of the harness at the dash switch location. It appears that I need to be connecting based on the run/park description above and not think in terms of connecting those two.

R Stegs


There is a lot of confusion regarding the early GT wiper motor.

It looks like a later 2 speed model, but it is a single speed only.

The big difference is that it is a single speed motor with regenerative braking. This design of motor was used on the GT to ensure the wipers stop in the park position and don't windmill due to the added momentum of the longer arms and blades.

The early roadster wipers have 3 wires.

The early GT single speed motor with regen. braking has 4 wires.

The later 2 speed motor used in both the GT and roadster has 5 wires. The 5th wire is the high speed feed.

To fit the 4 wire wiper motor to the GT a small 4 wire subharness was added. The harness comprises of a plastic plug (the same as used on the later 5 wire motors, but with one terminal unused) which has three 5" long wires terminated in insulated male flat blade connectors and one longer (red/green) wire terminated in an insulated female connector. The three short wires connect to the regular roadster wiper connections and the fourth wire follows the harness back to the wiper switch.

The GT wiper switch is unique and has four terminals. Only three are used. The switch shorts the motor feed lead when in the off position which brakes the motor shaft.

Hope this clarifies things.


I've attached an image of an original harness connection from an unmolested 1967 GT. The black vinyl tape is original and is not owner installed.

KJ Dodd

Further clarification:

To make things more confusing, the early GT motor has a switched ground, just like the roadster.

The later two speed motors used a switched power feed.

The connecting plug with four wires for the early GT motor is the same design as the 5 wire plug of the later 2 speed. But the wiring color code is reversed.

Later 2 speed:

1 - Ground (black)
2 - Auto Park (brown/
3 - High Speed (blue/lt. green)
4 - Motor power (Green)
5 - Normal Speed (Red/lt. green)

Early GT

1 - Power (Green)
2 - Auto Park (Black/Green)
3 -
4 - Ground (Black)
5 - Normal Speed (Red/Lt. green)

Early GT switch operation:

Off - Switch lever up - Black/Green connects to Red/Lt. green)

On - Switch lever horizontal - Black connects to Red/Lt. green)

Switch terminals:

1 -
2 - Black/Green (Autopark)
3 - Red/Lt. Green (Normal Speed)
4 - Black (Ground)
KJ Dodd

Thanks guys! Kelvin your description is exactly what I needed to sort this out. Confusing to say the least, especially since the mainstream wiring diagrams available do not really depict this GT issue.

The wiring of the switch is the most critical part of the problem in my case as the motor, original motor harness and wiring were all correct. I thought I needed a multi terminal two speed switch. I will use a regular off/on switch and give it a go!

Not a lot of units affected by this probably but one of those nice little tips in the Moss catalog would be neat! Especially since you sorted it out so well.

Many thanks!
R Stegs

Hi Guys.

I have converted my GT with the round body singe speed to a later model 2 speed. To do this, I used female spade terminals instead of a plug harness.

The parking switch came apart last year and I am working on replacing it. Unfortunately, when I pulled the motor, the wires came off.

The description above does not help in that the new parking switch does not have any wire numbers on it.

Can someone translate how the wires go. Using the 5 terminals in the parking switch that the wires from the car hook to. There are two rows of two spades with a third at the top turned 90 degrees.

Outside two and the one at 90 have wires going back to the motor. (only three wires going from the parking switch to the motor.

I have 5 wires coming from a 3 position dash switch.
Bruce Cunha

If you now have the later 2-speed motor, the park switch/connector block connections are here:

Schematic here:
PaulH Solihull


Your assistance with this topic is greatly appreciated. I don't know what I would do if there were not folks like you compiling this information.

Thanks Again, Bruce
Bruce Cunha


One other question. On the new three way switches, there is not a #2, #5, or #6 terminal. Only 1, 3, 4, 7, 8.

Everything hooks up per the diagram with the exception of #2. 1 and 7 appear to be connected, similar to what is in the diagrams.

Bruce Cunha

To be safe you would need to test the switch, but it's complicated by not knowing which way up the switch should be! Also the switches were often generic with more spades than need be, which may or may not be connected together internally.

On that schematic terminals 1, 3, 5 and 7 are all connected together internally (but may also have one or more external terminals).

With the switch in the 'off' position, 1 and 2 and bridged, and so are 5 and 6. This effectively connects 2 and 6 together, which are 'park' and 'slow'.

In the middle position 3 and 4 are bridged and so are 5 and 6, which effectively connects 4 and 6 together, i.e. 12v to 'slow'.

In the 'fast' position 3 and 4 are bridged and so are 7 and 8, i.e. 12v to 'fast'.

When the wipers are switched off, but the blades aren't parked, 12v comes from the park wire via the park switch on the motor, is connected via the switch to the 'slow' wire, which runs the motor until the park switch opens.

It's a matter of finding out which pairs of terminals are connected together in each of the three positions, bearing in mind you don't yet know which way up the switch should be, and matching them up to the interconnections I give above, good luck!
PaulH Solihull

Paul and I have been communicating off the board and it appears the three way switch that is sold through MOSS and VB are not the wiper three way switch. The one they sell does not have the #2 terminal which is needed to attach the parking system for the later two speed motor.

I have received a few web pages from the UK with the correct switch, so hopefully, I can get one here in a few weeks and finish this out.

BTW. If you don't hook up the park, the switch works just fine for the two speeds, you just have to time your shutoff so it parks the wipers. I did this for a number of years and it gets to be pretty easy.
Bruce Cunha

That Moss etc. switch *is* OK if you have the 2-speed motor with the earlier parking arrangement, just not for the later parking arrangement. The one from Holden is suitable for *both* types, and cheaper. It's also suitable for the lighting circuit, as ironically the switch intended for that, despite being simpler, is more expensive! It's also suitable for 2-speed heater fans. It also makes you more attractive to women, cures baldness ...
PaulH Solihull

A very impressive switch. RAY
rjm RAY

This thread was discussed between 07/01/2012 and 07/02/2012

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