MK 6 Switchbox

Peter Sewell · Joined: 21 Dec 2006 Posts: 4

I have removed and split the two halves of the switchbox, removed levers and starter button and had face refurbished. I know I have reassembled all parts removed correctly and the switch fits together perfectly. Before refitting to car I tested the electrical circuits as per the service manual procedure by connecting battery neg cable to neg terminal on switch. First three tests OK as per manual but when master switch and ignition on test carried out no light on terminals 2,6 and 11. If continuity tests carried out as per diagram in top right hand corner of wiring diagram then all checks OK. Is Service Manual procedure incorrect ?
Thanks
Peter Sewell

Christopher Carnley · Posted: Tue Dec 01, 2015 6:59 pm Post subject:

Is the car positive (as original) earthed, or changed to negative?

Peter Sewell · Joined: 21 Dec 2006 Posts: 4

Hi Chris
Car is still original positive earth but for testing switch out of car this would make no difference.
Peter

Christopher Carnley · Posted: Wed Dec 02, 2015 9:42 am Post subject:

Peter,

I should have realised that you meant the test lamp! (Bad day with the Derby job!)

When you test for continuity, what were the resistance readings when the two switches were in the on position?

Peter Sewell · Joined: 21 Dec 2006 Posts: 4

Chris
Thanks for your interest in this problem.
Master and Ignition switches on - resistance readings
Terminal 2 open circuit
6 open circuit
8 0
11 open circuit
Do you know if the two brass cams (one inside and one on outside) should be electrically connected ? They are on the same shaft so turn together but as I have not disturbed anything in this half of the switch I don't know if they are insulated from each other. The diagram in top right of vehicle wiring diagram suggests they are insulated from each other.
On mine there is no circuit between them.
Peter

Christopher Carnley · Posted: Wed Dec 02, 2015 6:13 pm Post subject:

As these connections are to important parts, ie fuel pump, ammeter, body junction boxes, I think that you should contact an auto electrician.

I have so much on just now, that I have no application to dismantle a switch box.

As Will Fiennes says, "Good luck. (with it)".

Malcolm Gordon · Posted: Fri Apr 29, 2016 8:12 pm Post subject:

Sorry to be coming onto this topic so late so you may already have solved your issue.

I had a suspect switchbox because I lost all electrical power on my recently completed Special. When the tests were carried out according to the workshop manual it would suggest it was faulty.

Another switch box which I had access to was checked and came back with the same problems. I was amazed that 2 could be faulty.

A third that I was able to gain access to which was in immaculate condition came back with the same fault when checked against the instructions in the workshop manual.

The conclusion is that the check procedure in the workshop manual is incorrect which is most unusual for Rolls Royce!

The whole problem I had in the end was a dirty connection to the ammeter and didn't require the switch box to be taken out and checked in the first place!

Stephen Blakey · Posted: Fri Apr 29, 2016 9:18 pm Post subject:

Hi Malcolm,

Thanks for that. Something for me to bear in mind when I come to fit the switch box to my own special.

Any chance of some pictures of the yellow peril? I followed your blog until you stopped blogging to concentrate on building, which is understandable. You told me, at Greetham, about your cunning plan to use a Morris Minor bonnet as a boot. Did you go ahead with that? Congratulations on getting it finished.

Stephen

Malcolm Gordon · Posted: Sat Apr 30, 2016 10:13 pm Post subject:

Hi Stephen,

Yes I finished my Special. I used it last year for the first time but unpainted. It was on the road 4 years to the day after starting the project. I have now just finished having it painted. I have just posted photos on the Welcome Members and their Cars section on this forum. I did go with the Morris Minor bonnet at the back of the car - well remembered.

It was last year when we had the electrical problem that took a week of head scratching and a few choice words to fathom out a switch box issue which in the end wasn't the problem. It was good to have a spare switch box and then a visit to Angus Bethinussen who is building a car to check out another. We really thought we were going mad when checking the info in the Workshop Manual when 3 were at fault.

In the end it was found to be the wires to the ammeter which were the cause of all our problems. These were swapped about so the ammeter read correctly when converting from positive to negative earth but we should have cleaned the terminals more!! You live and learn!

Stephen Blakey · Posted: Sat Apr 30, 2016 10:40 pm Post subject:

How many of us would clean those terminals before putting the wires on? You did well to find that! Sounds very frustrating.

Peter Sewell · Joined: 21 Dec 2006 Posts: 4

Malcolm
Thanks for your interest and the switch is back in the car all working correctly. After dismantling and reassembling and retesting over a period of one week the right conclusion is that the testing procedure in the manual is not correct.
Peter Sewell