Dynamo disaster

Hi, my 135 stopped charging around 18 months ago so i fitted a new dynamo and regulator and all seemed fine, about 10 hours work later and the dynamo failed, we thought it was a dynamo fault so fitted another and all seemed ok, then about 5 hours work later the new dynamo failed so we put it down to a dodgy regulator, fitted another new dynamo and a new regulator and all seemed fine, i have had the tractor in pieces for a few months doing a few oil leaks etc, when i started the tractor today for the first time after the work had been done it wasn't charging so i tested dynamo with multimeter and was only putting out 0.5 of a volt at half revs, quickly took dynamo to pieces for a look and everything seemed intact but i noticed there was no magnetism on the stator (should there be?), and it smelt burnt. i have fitted a new wiring harness recently and always polarized the new dynamos on the small connector, i can't think of anyting i could of done to make it eat dynamos, i recently got the fuel gauge working again but that was just that the float had gone past the stop and couldn't get back (easy fix), i also noticed that someone has added a earth wire that goes from the neg terminal and bolts to the dash, is this neccesery?, the tractor has all headlight harnesses and indicator wires removed, it has no wiper or anything only the essential fuel gauge and ammeter. any ideas why it has a fetish for dynamos?. Steve.

The circut cut out on the oil preasure gauge is not working or missing? So when you shut the tractor off your DYYYNAAAMOOOOOs get fried? Where do you guys come up with this stuff anyway??

I didn't think the gauge had electronic cut out switch so i'll check.

Dynamo is just another term for generator. Many UK manuals are written using that terminology-nothing wrong with it. If the oil pressure cut out switch, which is screwed into the oil pressure gauge, was sticking on with engine off, your electric gauges- most noticeably the fuel gauge, would continue to read after the engine is shut down, instead of going back to E. If this is the case, Hand Clutch is on the right track. If not, your problem is elsewhere.

If I remember correctly, 135 tractors are negative ground, so the ground wire shouldn"t make any difference. Let us know if the oil pressure switch is the problem.

think you owe Hand Clutch apology!!!! think he is a lot smarter then you. looks like your a new poster not the way to start things off

Hi, just had a look at the back of the gauge and there doesn't seem to be any switch on it, it only has single oil line from the block going into the centre of the gauge, just to clear up tractor is a 1976 MF20 industrial uk model (similar to 135), does this make any difference?, another thing i have noticed is the tractor has to be revved upto 1/4 throttle before the fuel gauge registers, thanks

Sorry!! Best Regards Hans Culcthenson

I should have specified that only the diesel tractors have the oil pressure switch. The gas tractors don"t have it because the ignition switch cuts the power.

Thanks again, my 135 is a Perkins diesel, but it looks as if the gauge is just mechanical, so does that suggest that the charging is linked to the ignition switch instead of the oil pressure switch?

If someone has installed an off-on-start key switch instead of an off-start key switch, the circuit controlled by the oil pressure switch is probably now controlled through the key switch, I would assume. BUT, I am not sure if the UK built MF 20 has the same wiring as the US built 20. I don"t know why it would be different, but you never know. The only way to know for sure if everything is hooked up right is to get a wiring diagram for your UK built tractor. I would say this for sure. Something is hooked up wrong if your fuel gauge only starts reading when the engine is revved up. That indicates that somehow, the fuel gauge circuit only activates when the generator starts putting out enough voltage to close the cutout relay in the regulator. It almost sounds like the fuel gauge circuit is looped in with the charging circuit, which it should not be. I think getting a wiring diagram is your next step. I could come up with one for you for the US built 20. If you would like that, contact me through my email.

Steven, a few posts down from this one is another one entitled ""MF 135 Fuel Gauge". On that post, David P, South Wales has posted the wiring diagram for a UK 135 which would be the same as your 20. It should help you out.

Thankyou MHMalcolm,

I have a wiring diagram with the owners manual and everything is definately where it should be, i'll keep head scratching, thanks for your views, much appreciated.

(quoted from post at 09:46:09 11/16/09) Thankyou MHMalcolm,

I have a wiring diagram with the owners manual and everything is definately where it should be, i'll keep head scratching, thanks for your views, much appreciated.

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Would it be possible for the fuel gauge or ammeter to cause problems if either of the gauges themselves were faulty i.e. shorted inside etc?, just a thought.

The Amp Gauges can short out. The fuel could also but that does not happen very often.

Thanks, is there an easy way to test ammeter and fuel gauge?, thanks.

On our 135Uk there is not a oil pressure switch. The guages are powered through the voltage regulator, and when it stops charging the guages are shut off.

Thanks TimMiller, much appreciated matey. Steven