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Post by jeff on Dec 29, 2020 17:41:21 GMT
could be a theory Nick.
Although the motor is not (as far as I know) been wired backwards. I havent been in that deep recently...too cold.
If we assume its wired correctly, but the polarity is reversed on the battery and dynamo flashed accordingly, would that not have the same effect in a timed motor?? just a thought. Mind you, the wiring in general has been mauled about in its past, and tidied up quite well by the PO. .
Its a real head scratcher this one, and as an old man told me many years ago, all faults are easy to fix, its just a matter of finding it by methodical elimination. hopefully without tearing the whole loom out.
I once had a terrible fault on a VW Passat which cut out as soon as the engine was warmed up. I tried everything. Then I woke up in the middle of the night, with a flash of inspiration, consulted a Bosh fuel injection manual. AHHHHHH. next day off to the scrap yard for a temperature operated fuel pressure regulator. Sorted. Perhaps a bottle of red might do it.
I do appreciate you guys scratching your heads too. I spoke to Tony Wood from LOCI, who I know has all his 3 MK! cars on negative earth. None of his cars have this fault, nor has he ever heard of it.
Once I get a lead, or crack the problem fully, I will shout it out on this site for all to see,
Jeff
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Post by jeff on Dec 29, 2020 18:01:07 GMT
Just a thought: All the green wires under the dash and controlled by ignition switch on fuse A4 are joined in parallel at a common point on the voltage stabilizer input. I wonder if the VS has a fault allowing an earth to continue after ignition is switched off  ? Just thinking out loud. |
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Post by jeff on Dec 29, 2020 20:31:55 GMT
I've decided I'm getting myself and friends into long grass here.
I've read some good posts on an MG post about continued engine running for a couple of seconds when switched off, with the lights on. It turned out to be a bad lighting earth allowing a "sneak" current finding a path to earth via coil and distributor.
So, back to basics as advised at the start of this thread. As the run on only happens with the heater fan on, I'd better start there and give all earths another seeing to.
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Post by 1800heap on Dec 29, 2020 21:38:18 GMT
Hi Jeff
Mk3 cars have seperate supply and fuse from the ign to supply the fan so they disconnect when the ign is switched off as they have a 4 poll switch. This says something about fans!
Can you tell us how the ignition light reacts when you turn the ignition off with the fan on and the fan off please.
Changes in brightness might be important too.
I think perhaps the dynamo control box is playing a part possibly but suspect the only cure will be to seperate the coil and fan supply like the Mk 3 does. This could be done with a relay.
Nick
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Post by 1800heap on Dec 29, 2020 22:06:19 GMT
Having said that a diode would be easyer to fit than relays and would do the same thing. It would need to be a high current one though.
Nick
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Post by jeff on Dec 29, 2020 22:13:21 GMT
Thanks Nick.
I revved the car up a bit before switching off the ign. The heater quit instantly but the engine ran on for a bit longer with the ign light glowing brightly until it stopped. I will have a good look at the wiring under the control box, and if I can swap it with a good known one.
To rewire the circuit isn't a big problem but I would like to find the cause. It must have been good sometime, and from what I gather, polarity doesnt seem to be an issue on other cars.
The only major electrical difference I've made is to fit a 2 speed wiper which required an extra wire and two gang switch. I fitted a clock, and a USB phone charger incorporating a digital volt meter. Only the wiper is switched as original via the ignition switch.
There are various things I can try if I dont find a bad earth. One being a rerouted supply.
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Post by dave1800 on Dec 30, 2020 2:01:43 GMT
People are reporting a similar issue with electric radiator fans that are not controlled by a relay. As mentioned a diode in series with the fan feed has been reported as resolving the issue but the diode gets pretty hot.
The thin ground feed to the RB340 was often the cause of regulator failure or odd symptoms and the remedy was to fit a more substantial lead grounded under the box. Not sure if it was the wire itself or a junction.
A motor with a field coil still provides a back EMF from the residual magnetism. That is why when changing the polarity you flash over the dynamo to change the direction of the magnetic poles. This is not very strong of course.
It will be interesting in due course if you manage to find the cause of this baffling symptom. You can't get energy from nowhere and the potential sources to feed the coil for a couple of seconds are the fan motor, dynamo and battery. As turning the fan off stops this, the fan or its wiring must be the root of the problem in my view. I am often wrong however!
Good luck
David
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Post by 1800heap on Dec 30, 2020 3:26:07 GMT
I agree David You would still get back EMF from a field coil motor. I don't think the motor timing would have as signifcant an effect though if wired backwards. Jeff so you said the ign light stays on brightly until the engine stops. This I find odd! You didn't mention what the ign light does when the fan is set to off and you shut down the engine? If it were me I would try removing the ign lamp bulb and see what effect that has. I suspect it may make a difference. It should also stop the dynamo contol box getting any back emf from the fan in case the dynamo is producing the effect via the fan Next I would put it in the too hard box, give up and put a big diode in the fan circuit! I would want something that can handle 30+ amps so that a dead short will blow the fuse rather than melt the diode!  Nick |
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Post by dave1800 on Dec 30, 2020 4:02:33 GMT
I agree with Nick, the ignition warning light may be part of the issue but not sure how much current the ignition coil needs to keep the hot engine going. More than the lamp could pass I suspect? Maybe the easiest solution is to do nothing if it's not causing a problem!
I think the warning light will come on momentarily when you turn off the engine anyway if there is a route to ground from the "live end" of the bulb through anything that is wired through the ignition switch that is turned on before the dynamo output falls to zero.
If we look to see what could keep the ignition powered for around 2 seconds, as far as I can see there are only 2 components. The fan motor slowing down and the RB340 cut out hanging but I can't see how the latter could power the coil.
An alternative to to a diode nowadays is a power mosfet transistor with a zener diode. You can get them now for little money and with such a low on resistance would stay cool. I will provide details if you really want to give it a go.
David
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Post by jeff on Dec 30, 2020 14:52:30 GMT
Nick, I removed the ignition light from the circuit by disconnecting from the WL connection on the control box. But no difference.
I also disconnected the switch wire under the dash and have positive volts 10.5 ign on So that bit is the right way. Oddly, it's a newish looking yellow wire with a none standard lucar connector. I dont know yet where that goes to, so maybe there has been a burn up in the past overheating the field coils.
The heater model is FHR 5401 04, which I know is not the original unit. According to maintenance records the heater was replaced with a reconditioned unit in 1989. Whatever model it is, it doesnt blow enough to put a candle out. Maybe it came from a later car. More digging I reckon.
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Post by jeff on Dec 30, 2020 15:03:14 GMT
Edit: the voltage 10.5v+ was measured across the switch wire and the black wire connected to the switch mounting bolt on the heater body. That voltage seems low even with the ign on. Although the current would be passing through the motor coils at that point I think? I could of course run a wire directly from the black earth wire directly to battery earth as a trial. If that trial cures the fault then it confirms an earth fault elsewhere.
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Post by 1800heap on Dec 30, 2020 22:20:50 GMT
Hi Jeff
That voltage does seem rather low!
When you disconnected the ignition lamp via the control box the lamp stayed off but the car still ran on, so that confirms the wire you disconnected is where it should be on the control box and tells us it is the fan/fan wiring causing the issue I think. It might be worth waiting to see what David thinks but from his assesment b4 I think we are both on the same page.
I can't tell you by your numbers what you have but someone may be able to. You have a Lucus heater with a metal body don't you? I think it is only the Oz crabs that had a plastic body anyway. Beware anyone with a plastic body heater as it probably contains asbestos!
I can tell you that the metal body of the heater assembly is rubber mounted and is not a good earthing point, which is why the fan wiring contains an earth wire. It is not clear to me where you are testing with your meter for voltage. From the fan switch to the heater body? You can't use the fan/heater body as I said you may get a funny voltage doing that even on a good one.
Earthing could be the issue. My car had some wiring issues and a bad connecton on the bulkhead plugs caused one of the bukhead plugs to melt so you are wise to keep digging at this point I think, given the low reading. You do get some voltage drop but that seems too much. Check voltages with the fan running and ground the meter to the car body. Its a good idea to get a battery voltage too for comparison. You can also check the voltage of the heater ground wire to the car body.
Nick
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Post by dave1800 on Dec 31, 2020 2:39:13 GMT
Yes, that takes the warning lamp out of the equation other than it shows the voltage is still present for a couple of seconds. From my understanding there have been a number of different heater blower motors and the metal case is insulated from the car body. If this insulation fails then it will cause a short (we had a report of this a while ago).
As Nick says the voltage you measured appears too low assuming your battery voltage is healthy. I think the first thing is to check whether the motor is actually working properly when given the full battery voltage. I would suggest running a temporary power wire (important with a 20A fuse in-line) from the battery to the motor and also an earth lead to the body or preferably the battery earth side. (Also try the motor with the wires reversed but ensure the case is isolated from the body)
If all is well then :
reconnect the motor earth lead to its original connector see whether that ground is good - if not remedy the fault. As Nick says measure the voltage between the earth lead and a good body ground. It should be <0.2v with the fan running.
You can then reconnect the original fan motor supply lead and check for voltage drops. Initially connect the voltmeter between the battery positive and the fan motor connector. Turn on the fan. If there is a drop of >0.5v then you need to follow the wires and connectors taking measurements until you find the drop. It can be a loose of corroded connector or a partially broken wire. It is also possible that someone has connected it up incorrectly in the past. (Just a thought the voltage you measured is fairly close to the voltage stabiliser output and the fan supply wire junctions at the stabiliser input).
Remember you need to keep the circuit loaded to find voltage drops. If you don't wish to keep the fan running you could use a 12v 21W brake light bulb instead, you need sufficient load to be able to find the voltage drop which is proportional to the load current.
This will hopefully sort out whether the fan and wiring are sound, but still leaves the running on to address.
David
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Post by jeff on Dec 31, 2020 14:54:19 GMT
Well well guys, thanks for all that..
The two wires I accessed today were the ones that emerge from a channel on the face of the Smith's heater body. One yellow, one black. The yellow should be green and has a remade end proving a previous encounter with humans. This is connected to the sliding switch terminal.
The black wire is anchored to the supporting bolt of the sliding switch and looks like it should go there. I see no other reason why the black should emerge there, with the yellow wire, if it wasnt supposed to be there. All of that if fitted to the parcel shelf support bracket which is earthed. Only the switch teminal has an insulator when in the off or Ram position.
Black wire disconnected shows no volts and continuity to earth.
Yellow wire shows continuity to earth, which might be via motor windings when ign off but also shows 15+V when disconnected and engine running. I would expect to see that. When I measured yesterday engine was not running, just ignition on. The 10.5+v was probably down to my connections. At that voltage the battery would be dead flat, and it's a new one.
Static battery voltage 12.6V stone cold -1c.
Connect black and yellow wires together fan runs so proving it's connected in series via single pole switch as per WM.
Heater body is mounted on rubber bobbins but is still earthed. I haven't yet got up to the right side to find entry wires as my fingers were freezing off today.
Somewhere I have an good single speed heater motor from a negative earthed mgb, which I changed for a 2 speed. I guess it's a similar type so I can hook that up and see what happens....when I can find it.
If that shows similar results then I will be into the wiring.
I will let you know I get on.
Jeff
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Post by jeff on Dec 31, 2020 16:28:19 GMT
It gets worse. First, I cannot see a way to get my big hands up between the pedal box and the heater side plug. After pulling the parcel shelf top edge down I can see the connector...right behind the screen duct. No way can I get in there without pulling the parcel shelf out...groan..
I disconnected the rev counter in case but engine still ran on when switched off and it did. Then it all went wrong. Engine wouldnt start and no ign switch powered stuff would work. But ign light and oil light on. I fiddled with the ignition key and all came on. Engine started but fiddling with the key would stop the engine and leave Fan running. There seems a point a fraction after ign on where the aux circuits go off and on at random. I wonder if the ignition switch being faulty could be the issue with engine not cutting immediately with fan running. Seems a bit weird but.....I dont yet see how unless contacts are falling apart and shorting some how. My brain is overheating while I freeze. Something is wrong with that switch and it will have to be eliminated.
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? Just thinking out loud. 
