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MG MGB Technical - ignition switch fault

HI guys,

I know from reading through the archives this subject has been covered possibly hundreds of times.
My exscuse is that having been away from mgbs for quite a number of years i need a bit of reassurance on this subject.
I had forgotten what "fun" (ha ha ) mgb electrics are.
Having found a fault in my steering column stalk switch, namely head light full beam not working i replace the whole unit which cleared the problem.
Feeling pleased with myself i tried to start the car only to find zilch response . Appeared dead as a dodo except all electrics alive& well ,all lights shining brightly etc.
Imediately suspected i had disturbed a wire or connection somewhere amongst the maze under the dash.
But nothing to be seen . On more detailed research i suspected that ignition switch was faulty . Power on the brown wire but not making connection to the red/white wire that goes to the starter relay.No power at that end , hence not firing up starter.
Just wanted to know before i start laying out money on new switches etc if there is anything else it could be?
On hot wiring the brown & red/white the starter turns over ok.
Also dont want to replace the whole switch & steering wheel lock mehanism, can i just replace the elctrical switch connection. I note there are quite a few online but look different to my one on my 72 mgb. Thanks for your forberance but your adcvice would be appreciated . Thanks, Ken
k proud

could you take just the electrical switch out and see if you can clean, and if required repair, the internal or external connections

but do make a note, or photo, of the positions of the wire connections - I know some one who thought he'd easily remember only four positions but then later found he couldn't ;)
Nigel Atkins

Does the ignition warning light come on i.e. power on the white? How about on the white/green in the accessories position? But if you are certain there is power on the brown terminal of the switch itself, i.e. not just on the harness end of the wire that connects it to the harness, and likewise there is no power on the white/red terminal of the switch i.e. not just on the end of the wire that connects it to the main harness, then the switch would appear to be faulty.

The switches should be replaceable, just a grub-screw securing them to the lock/column.

However as far as noting the wire colours go that is dependent on the new switch having the same as the old, which isn't always the case.

It's quite easy to work out which is which.

With the switch off all the wires are disconnected from each other.

In the first on position - accessories - brown is connected to white/green.

In the second position - ignition - brown is connected to white and white/green.

In the third position - crank - brown is connected to white/red and white, but disconnected from white/green.
Paul Hunt

Thanks guys,
I am pretty sure it is the ignition switch, cant see what else.
Looking at the ignition switch location looks very difficult to remove set in the steering lock mechanism.
One bold head still there , but other sheared off.
Read of various ways of getting around this such as drilling out , hacksawing slots etc , but all look difficult due to location. Seriusly thinking of getting a straight forward ignition switch to locate in the pre 1972 location on the dash , hole still there now used by the windscreen washer button. Can run wires straight up from existig location. leave steering lock on but will have to use old key to leave in situ to keep unlocked .
All in all seems an easier option, unless you can see any probs with this ?

Ken
k proud

H,

You should be able to buy just the igntion/starter switch as a seperate part.


It's secured by a very small screw into the sterring lock housing. If you can find one it's much easier than replacing the whole assembly.


Having said that its not too bad a job, just drop the three bolts that hold the top of the colomn. Then it will drop down a bit allowing better access. A sharp pointed drift should get the sheer bolts moving.


Hope that helps a bit.


Regards Steve
SR Smith 1

Hi Steve, cant see any grub screws . do you mean where the electrical connection go in? There are two normal screws that on what appears to be a connection plate but cant get a screwdriver on very easily. Maybe i will try lowering the steering column. If i get that far and do want to get the whole assembly off do i then need to remove the steeering wheel ?

Thanks
Ken
k proud

Hi again,


What year is this car?


And can see a makers name on the switch? Lucas, Neiman etc?


The way they attach differs.


Regards Steve
SR Smith 1

"You should be able to buy just the igntion/starter switch as a seperate part."

That's what the Parts Catalogue implies. Look at the parts houses, if they supply the switch on its own (whether or not they also supply one with a lock) then it must be replaceable. Mind you Clausager says it's quite possible that steering locks of different makes were fitted at the same time, which would almost certainly mean the switches were different as well. Another reason to determine the manufacturer which could be Neiman, Trico, Magnatex, Wilmot Breedon or Lowe and Fletcher.
Paul Hunt

Ken - I fitted a replacement ignition switch to one of my cars, a 1979 BGT. Bought it from here:
http://www.ebay.co.uk/itm/MGB-MGBGT-Ignition-Switch-BHA5292-for-Lucas-steering-Lock-BHM7144-/221264653631?pt=UK_CarsParts_Vehicles_CarParts_SM&hash=item338466ad3f
The switch was held in place with a small screw as described by Steve, and I replaced it without having to remove the steering lock.

The Moss parts catalogue lists the steering lock with ignition switch as part number BHM7144X (the 'X' means it's a repro part), for all MGBs '72 on. I bought one of these a while back for my other B. I had to lower the steering column a bit to remove the plastic cowls and access the shear bolts; I think I had to use a Dremel with grinding disc to make screwdriver slots in the bolts.
Brian Shaw

Hi ,
The car is a 1972, and cant see any markings on the lock body as far as i can see. I think the whole lock mechanism is shot as fiddling today had difficulty turning key properly. Gave a good dose of wd40 but made it worse if anything. Going to replace the whole lot i think . Dropped steering column as suggested and does make a little easier. Got one bolt out , but other head already sheared. Tried a drift & cutting slot but cant shift it. Will have to cut through bolt i think somehow ,
Angle grinder ? Lot of sparks but maybe !
May do away with steering lock ignition fit a pre 72 ignition as i mooted. I noted today how easily the lock came on , a slight turn back of the key . A bit worrying
when drivng unless this is a fault too .
Thanks for info so far guys .
ken
k proud

Hi,

You might as well angle grind it off it that case, the new one will be complete with a new clamp and two new sheer bolts.



If you see the numbers next to the terminals and they read 1,2,3,4 and 5 it's a Lucas part.


It it's marked 30, 15, 75 and 50 it's probably a Neiman as that is the european standard designation.


It's not a major job to take out the whole upper column if your concerned about damaging the interior trim whilst attacking it.


Regards Steve
SR Smith 1

Curioser & curioser as alice said.
Have now got the offending ignition lock/switch off by judicious use of an angle grinder. Now i can get a proper look it is a bosch. Numbers are 75,50,15,57a, 30x2, ie 6 connections.Similar to what Steve described. Have connected up new one to try , althoughnot in situ & works fine im glad to say. Was beginning to think there may have been some other problem lurking . New one says Lucas , although made in Taiwan, looks quite well made though. Has just 4 terminals which helps my confused mind! Another problem solved hopefully , now onto the next ! Thanks a lot guys , all the info was very useful .
Regards Ken
k proud

Hi ken,


Sounds as if you have is sussed.


The brown/s attach to 30.

White/s to 15.


White/red to 50.

White/green? to 75.


Ignore 57, it's a feed in the off position for parking lights via the indicator stalk on a continental car.



Glad you got it sorted.


Regards Steve.
SR Smith 1

Ken,
have a look at Paul's excellent web site mgb-stuff as it will show you the wiring for the 72 UK MGB ignition switch with 4 terminals

(Steve, you're wiring up the old switch)
Nigel Atkins

This thread was discussed between 21/03/2014 and 25/03/2014

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