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Author Topic: Electrical Connections  (Read 5167 times)

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Electrical Connections
« on: December 05, 2007, 04:07:33 PM »
I need a little help. I was pretty good about taking photo’s of everything and putting stuff in baggies and labeling the bags.
My confusion now is that I only have one switch and it seems like the Pressure Failure switch (see the first picture below). I am surprised if I lost the Stop Light switch because was very careful taking this all apart. That is why I am not sure there ever was a Stop Switch. While it is not impossible, I am surprised I would have not taken a picture of it, put it in a bag and label it. I took the pedal box out, had it sand blasted and painted so I think I would have seen it and taken it out.
There is a threaded hole in the pedal box over the brake pedal so it seems like there may have been a switch there. I just don’t remember it or have it documented and the threaded hole may have been used in prior years.
My confusion is if you look at first picture below, the green barrel connectors hanging off of the switch plug neatly into the connectors on the harness wires (see second picture). The harness wire extends about another 1 ½ feet with a plastic connector at the end. I think the plastic connector may have plugged into the Stop Switch in the back of the pedal box. I am just not sure. The thing that further confuses me is that if I connect the two green wires on the harness it lights the brake lights! Since the switch in the picture definitely came off the Master Cylinder and since when the green wires are connected (touched together) the brake light turn on, l thought maybe it was a dual purpose switch. I am just not sure.
In either case, do the two green wires with the barrel connectors coming off the harness look familiar? Does the plastic connector at the end of the wire look familiar? Are the two barrel connectors for the Pressure Failure Switch and the plastic connector at the end for the Stop Switch?
I put a few other pictures of the car. Maybe a little boring but certainly more interesting than pictures of my kids!!
Thanks for getting back to me, this is really helpful!
Robert Ditta

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Re: Electrical Connections
« Reply #1 on: December 05, 2007, 04:11:12 PM »
Hi Robert,

The switch in the first photo looks like the stop light switch.  It is the same one as in my 73 and both Victoria British and Moss show the same item number for yours and my year cars.  The pressure failure switch would have a top to match the connector on the hraness you have.

I found the Pressure Failure Switch in the catalogs and it's location, which is where you have the switch in your picture, and this explains a lot.  It is Victoria British P/N 8-3147 (74 1/2-75, about $20) or 7-424 (76-80, about $35) and it shows being on the master cylinder where your current switch is.  The sketch is small, but it looks to be a mechanical switch.  The top more closely matches your harness' snap-on connector. 

Now, what I believe is mixed-up is that the stop light switch is now in the place of the pressure failure switch.  The one you showed me is definitely the lamp switch.  It should be removed and relocated to the location you identified on the pedal box and the original pressure failure switch found or replaced and that should sort the problem in one fell swoop.  If the pressure failure switch is mechanical, as it appears, it is possibly a "dry" operation and should not leak if removed, so taking your present switch out shouldn't cause the master cylinder to leak or gulp air.  You can minimize the exposure by being ready to plug the hole with your finger and put the new switch right back in.  Since the switch is on the bottom of the master cylinder, as long as it does not run dry or the pedal pushed with the hole open, even if it does leak a bit, it should not suck air in.  You can then top it up and move on to putting the stop light switch in the right position.

To test the stop lamp switch operation, it should be closed (complete circuit/lights on) with the actuator pin extended and open (lights out) with the pin pushed in.  The 2 switches may work opposite (the pressure failure circuit open extended/closed pushed in), which is why they are not interchangeable.

I continue to find it amazing that the switches would fit in the same size hole with the threads.  This is not the only example of this I have found and it is not confined to British cars.  If one hole were 1/16" larger or smaller, they could not be mixed-up.

I hope that solves it for you.  Let me know what you finally do find.

Best regards,

American MGB Association
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Re: Electrical Connections
« Reply #2 on: December 15, 2007, 10:46:21 AM »
Art, I came to the same conclusion. I took a fresh look at the VB and Moss catalogues. Retracing my steps I think I see why I screwed up.
VB has it as Stop Light Switch (I originally could not find it as it was looking for Brake Light Switch).
While Moss has as Brake Light Switch I tried to find it by looking in the index that is in the middle of the catalogue. I realized there was an index on the last page and lo and behold, there it is listed as a Brake Light Switch. 
If I had found those pictures before I started to fix the brake lights it likely would not have gotten this far!
In both catalogues the Brake Light Switch looks like the one I currently have in my master cylinder and the Pressure Switch looks like it has the male side of that oval plastic connector.
My confusion was further deepened because I either mistakenly put the Brake Light Switch into the Master Cylinder or that is where it was and it actually worked. I don’t think it was that, I am beginning to think I just made a mistake.
So, I need to buy the two switches and try to replace the pressure switch like you said and keep my fingers crossed I do not get air into the system and hopefully avoid having to bleed the system again!!
The good thing is that Moss is right there in New Jersey. I am on Long Island and if I order it today, I may get it tomorrow in time for some more fun this weekend!!
Thanks again!
Robert Ditta


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