Faulty Ignition Switch?

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Steve6
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Faulty Ignition Switch?

Post by Steve6 » Tue Jun 20, 2017 11:45 am

Hello Everybody,
I need to pick your brains a bit if you don't mind. Last Sat my 1948 Rover 75 suddenly ground to a halt on the way to a local show. It was a sudden cut out, rather than any spluttering, so electrics rather than fuel were suspected. A passing mechanic kindly joined in, and we did all we could at the side of the road, but we couldn't get the car to fire. Of course it's embarrassing to break down so close to a show, because everybody stops to help, but thanks to all who did.

Anyway, got towed home and in the garage with the help of a multimeter, I now suspect the actual ignition switch in the dash, because I measure continuity from the coil to earth with ignition key OFF, but if I turn ignition ON and wiggle the key I can get intermittent continuity / isolation, in other words the car appears capable of turning itself OFF with the key in the ON position, perhaps on a bumpy road.

So first questions - Is my logic correct? Has anybody else had this issue?

Next questions - Does anybody have a good replacement key / starter button switch for sale? Can anyone suggest a later alternative switch that I could adapt and maybe fit under the dash? I'm not a stickler for originality if it means greater reliability.

Thank you for any help, advice, suggestions you might have.
Steve Evans

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luli
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Re: Faulty Ignition Switch?

Post by luli » Tue Jun 20, 2017 2:24 pm

Is the starter turning when you push the button? When you turn the key on, can you use the horn? Is there ignition light? If not, check for a blown fuse connected to A2. If the fuse is OK, short terminals A and A1 on the dynamo regulator and test again the above. If the horn etc work now, the fault is with the ammeter, switch or wiring. See more here http://wp.me/pXLKy-St
Rover 10 1946 RHD
Rover 10 1947 LHD
Rover 12 1947 tourer LHD
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djm16
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Re: Faulty Ignition Switch?

Post by djm16 » Wed Jun 21, 2017 7:12 am

I the power to the ignition is intermittent, and can be affected by wiggling the ignition key, then it is highly likely the ignition switch is at fault. They are in general very simple in design and can sometimes be fixed quite easily. I cannot claim to have done this for a P3, but P4 and 3 litre yes. The switch can usually be disassembled and then it is clear where there is oxidation or wear causing the problem. Clean, adapt or replace.

Steve6
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Re: Faulty Ignition Switch?

Post by Steve6 » Wed Jun 21, 2017 9:36 am

Many thanks to luli and djm16. I will begin a little investigation this afternoon, but I fear I am dealing with the original wiring loom, so I might be opening a can of worms! I have gently prised out the dashboard and removed the ammeter, so can now see the ignition switch reasonably well, so can now use my multimeter to carry out a bit of probing. It's nice to hear the switch might be recoverable. I know the starter cranks, and I know the horn worked until I removed the ammeter so that section seems ok. The loom behind the dash doesn't look great, so I'm thinking it might be a good idea to take every wire, remove and trim and fit modern shrink sleeving, just to reinforce the loom a bit.
If I can't find or fix the P3 switch, might it be possible to modify to a P4 setup?
Many thanks as always
Steve

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luli
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Re: Faulty Ignition Switch?

Post by luli » Wed Jun 21, 2017 12:26 pm

The external terminals of the switch are riveted to the internal conductors, then soldered. This is their weakness: The solder dreis, the rivet gets corroded resulting in bad contact. The fact that they carry high current just worsen the situation. Resoldering fixes the issue. A long term solution is to use a relay to carries the high current.
Rover 10 1946 RHD
Rover 10 1947 LHD
Rover 12 1947 tourer LHD
http://lulisml.wordpress.com/

Steve6
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Re: Faulty Ignition Switch?

Post by Steve6 » Wed Jun 21, 2017 1:53 pm

Thanks luli, once I get the switch out I will assess if resoldering is a possibility. It would be nice if that was the case. I seem to have reliable cranking on the button, so the high power contacts are probably OK, it's the low-power key operated contacts I am suspicious of. Thanks for your help, will report back.
Regards
Steve

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luli
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Re: Faulty Ignition Switch?

Post by luli » Wed Jun 21, 2017 5:06 pm

This is not the case. The cranking is done by a relay (solenoid) which draws 5 Amperes, momentarily, while the coil draws 3A continuously, and so do the wipers. If you drive in the rain, press the brake and use the horn the total current is almost 19A. Have you seen the inside of the switch in my link? See also here http://wp.me/pXLKy-Ky
Rover 10 1946 RHD
Rover 10 1947 LHD
Rover 12 1947 tourer LHD
http://lulisml.wordpress.com/

Steve6
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Re: Faulty Ignition Switch?

Post by Steve6 » Sun Jun 25, 2017 9:33 am

It really adds up doesn't it? Very surprising for a simple switch. I've now managed to extract the starter / key switch from the dash, and my suspicions appear correct, my multimeter tells me that it is possible for the key to pass through the 'ON' position to a point where it is intermittent. I'm hoping to locate a replacement switch but would also like to pull this faulty switch apart to see if it can be fixed as a spare.
Thanks for the photo of the switch internals luli, I'm now trying to decide how the switch comes apart safely. I can see the contacts are riveted through the bottom of the plastic 'bucket' and that the front probably rotates to be removed, so presumably the key barrel has to be pulled out first? Could you tell me how it comes apart please?
As always many thanks
Steve

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luli
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Re: Faulty Ignition Switch?

Post by luli » Sun Jun 25, 2017 10:43 pm

The switch "tub" is made out of bakelite, and has a metal cover, in which you see the lock cylinder and the starter push button. This cover is secured by 3 little tubs. Straighten them carefully and the switch will come apart. I will look later if I have some pictures.
Rover 10 1946 RHD
Rover 10 1947 LHD
Rover 12 1947 tourer LHD
http://lulisml.wordpress.com/

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