Talk Morgan Forums Morgan Sports Cars Maintenance & Servicing Diagnosis please?

Melvyn is still working (and processing orders)

And just had this from Allon White:

Thanks TBM

Ive just done some research and the BPS can have multiple functions depending upon the vehicle it is fitted to. On the Morgan it would seem that it reduces the flow of petrol when braking or may have other engine management functions.

On other cars it can be used to enable the car to be started on cars that require the brake pedal to be depressed when starting, It can also have an effect on engine management systems, traction and stability control, activation of cruise control, and locking the transmission selector in park in automatic cars.

So now I understand that it would seem logical that a faulty BPS could well cause the problems that both Heinz and Stuart have had.

Regarding the brake light switch there seems to be a difference of opinion over whether the momentary push switch used should be normally open (NO) or closed (NC). Clearly for the brake lights to operate the circuit must be closed. However this doesn't take into account the switch location and actuation. Given it has to work over a range of pedal movements in turn varying from car to car, it has to be mounted in front of the pedal with the switch plunger under some pressure with brake pedal in rest position, i.e. NOT the switches "normal" position. This requires a momentary NC push switch such that when brake is operated, pressure is taken off switch plunger and circuit becomes closed.

With this post you were very close to the issue.

Correction:
Stuart, I re-read the beginning of the thread. Sorry I forgot that you replaced the brake light switch (right switch). No need to compare...the old switch was certainly an NC switch as well, as Richard above also states and otherwise your brake light probably would not have worked resp. would be always on when not braking in the past. My request from last night was if you could see if the LEFT switch (BPS) is an NC or NO switch on your car.
But be careful before you measure the switch and apply voltage to it, disconnect both wires not to damage the ECU.

Heinz, you are asking if I can get my wife to get into the footwell to help remove the guard plate AGAIN!

Ok the switch passes current while foot is off the brake.

Jeez, I had ignored this thread as this stuff reminds me of being back at work and the frustrations of not having accurate data to work with, the excuse being intellectual copyright relative to programming or any access to it.. Having read the input there has indeed been good use of logical thinking though unfortunately as evidenced, that does not always resolve the issue for want of access to the ladder logic/map..

As I typed I tend to ignore this stuff and also diagrams where the wires are connected into the inevitable empty box/ ECU.

My thinking is well out of date.

Being a safety circuit, I would expect brake lights to be wired directly and not be wired through an ECU.

My memory is poor though I seem to have picked up on a situation of RUN-ON if the throttle pedal is released quickly and that this situation seem to persist on a number of vehicles relative to the complexity of the map..? If so then you can perhaps imagine a second switch on the brake pedal COULD be used to cut the signal to the fuel injectors thus cutting fuelling instantly,... ? Or not..!!!

I also note that there is mention of having to press the brake as being part of the start up sequence, which has been standard on some cars for a while, since there were many accidents caused by "issues" of many automatic cars moving off uncontrollably during start up. Lots of legal cases in the US.

There are so many variables relative to a secondary switch operated by pressing the brake other than brake lights that without information on it`s exact purpose, you are limited to playing a guessing game all be it with good levels of logical thinking.

I hope you forgive me for suggesting that there are instances of Morgan foibles relative to supply of wiring diagrams or even occasional use of other than the correct colour of wire for a defined purpose, thus when it comes to programming and even switch selection, there may be room for mistakes.... One only has to look at Boeing to see that those who write and supposedly test programming can make errors...!!!

As for NO or NC as I typed those switches can look identical and yet their internal contacts may be designed to function in an opposing way.

Normally such switches will be identified by a MANUFACTURERS part number i.e. XXXX/0 perhaps for a NO switch and XXXX/1 for a NC switch, but the number of digits can be in any configuration, and logic does not apply, as the last digits could be anything, I only used a one and a zero as examples of simplistic...err...logic..!!!

Having now looked at the pics in the thread it seems the plungers in the switches may be exposed to crud and thus could perhaps cause the plungers to partially stick causing intermittent switching action, and intermittent actions of switches and poor connections can be a nightmare to trace given some of the signals can be other than one`s or zeros, operate on low voltages or frequency related, having a top notch code reader guarantees nothing... unfortunately... sigh, but then I am but an old Luddite, best ignored...

Stuart thanks to you and great thanks also to your wife
I hope I am right and also that I draw the right conclusions.
Stuart you say:
"the switch passes current while foot is off the brake"
So it's a NO switch like in my car. In other words, it's the opposite of the brake light switch.

Here's what I have in mind: First, I think of you and your problem, Stuart. If there is a chance that you can or may drive again, please just disconnect the one wire on the left side of the left switch. It's very easy to do with your finger and thumb, and it's quite sufficient for a test. Please isolate the bare end of the connector on the wire and leave it there.
Then I am curious about your experiences a) if the fault is gone, and b) if the car drives better (after a few miles), especially the feeling of the throttle response.

If you had said that the BPS switch doesn't conduct current when the foot isn't on the brake, we would have had to keep looking for the fault...But this way we have a chance of finding a systematic failure. And there's a growing belief (or even hope) to me that we share the same symptom and the same cause.

If all goes well, we'll have a clue, and there really should be many or all of the drivers of a Sigma 4/4 checking the switch that has it on board. I don't know when that happened, but I mean, +8Rich said that his 2009 4/4 didn't have that switch yet?
Controlling the switch (or at least driving with one wire disconnected) is important to make sure it doesn't happen to affect just the two of us but to help the other drivers.

If all 4/4 got a NO switch for BPS and a NC for the brake light at least for a certain period of time, then coincidence can be largely ruled out.

My guess would be (purely logically, I don't want to offend anybody):
Either Ford says that it SHOULD be a NO switch for reasons Ford would have to explain, and which at least in my car lead to the bug.
Or maybe there was an error, a misunderstanding somewhere in the information transfer or training. And as a result, everyone in production has always made a conscious effort to the best of their knowledge and belief to install an NO switch on the left and an NC switch on the right in every brake pedal.
Or, another possibility, everybody does everything right, there must be two NC switches in each brake pedal but MMC got a delivery of wrong switches. But to be honest, this would have been noticed immediately with the brake pedal.

The question why most cars are symptom free and some are not I am very interested in but we can not answer yet. I have an assumption that is still half-baked. I tend to believe that when certain thresholds are reached from a combination of properties, the motor is throttled down during more steps. Perhaps first it becomes just leaner and when more reduce is needed the throttlebody will close in intervall as I could see it with the OBD2 during running the car. For example, I had the experience with an open K&N more explicitly (ok, I know, other riders don't have a problem with that). So I assume the engine that doesn't stutter is always leaned when revving up when this circuit is permanently activated and therefore it is not really symptom free in comparison to this circuit being off.

I actually find it hard to believe that the two switches would be planned different, as they look the same. More likely that they should both be the same but the someone grabbed a wrong switch by mistake. Heinz which way does your switch function, please?

Like yours if I understood you right and if you mean the left one which is not the brake light but the BPS switch. Current flows if the foot is not on the brake pedal.