Hi all new to the forum , hoping someone may be able to point me in the right direction , electrics is a dark art to me , spanners and hammers i can do 😁

Skoda yeti 1.6 tdi greenline 2011 ,130.000 miles sometimes it would not start . turn key and engine would wind over , glow plug light would flash and it would not start , release key and it will continue to wind over on its own , switch off and allow dash display to power down and 99% of the time it would fire up as normal after ,things got a bit worse recently , just a click from the starter then nothing ,then it would wind over and start , but the rear wiper would go on its own while turning over , also had and air bag light come on , heater control playing up . cold on hot , but then move to cold and back its ok , now we have the initial click of the starter , then its briefly try's to wind over but not enough to fire , battery was a little low so put jump leads of my JCB and tried with no change , tested starter with a hot wire and it wound over no problem , but would not start , checked and cleaned earths leads etc . tried again with jump leads and lost all ignition , nothing at all , all non ignition dependant functions work fine , no obd access just keeps asking for ignition on , did i have BCM problems and have now fried it , checked all fuses , swapped relays , can get ignition lights with power probe on to fuse thats all sitll wont access obd though

thanks in advance 👍

First impression Dozerman, is the battery fully charged?.

Test standing voltage. Should be 12v plus, normally 12.8+

With the engine running, it should go up to 14.5V

If you can do the test come back & tell us the results.

How old is the battery?

Edited 7 November, 20257 Nov by Carlodiesel

Hello, welcome to the forum.

Can you test the battery voltage while the engine is being cranked?

Check any earth connection to the engine for tightness and a clean contact.

Multiple seemingly unrelated electrical faults often indicate a common cause.

This might be things that share a common 12 volt feed. If you imagine the electrical system from the battery positive connector as a tree trunk dividing into branches and then smaller branches you will get the idea. The closer to the battery positive the fault lies, the more things are affected simultaneously.

Of equal importance are the earth returns, which is fundamentally the same as the positive supply but working backwards. Slightly more complicated by the use of the metal car body for part of the path. In this case, the closer to the battery negative the fault lies, the more things are affected.

I suggest you look again at electrical connections, starting from each of the battery connectors and working outwards. In my experience, earths are more prone to faults than the positive side, due to them being more exposed to weather. Of especial importance is any earth strap from the engine/gearbox to the body. These can sometimes corrode internally within the crimps and look OK but have higher than acceptable resistance. Just cleaning the ends isn't enough, replacement is best.

Bear in mind that starter motor current is much larger than for any other electrical item, so it's the first to expose weakness anywhere. Connections in this circuit must have resistance of no more than a couple of thousandths of an ohm. Testing this is way beyond the capabilities of ordinary meters, so just because something "buzzes through" it doesn't mean it's good enough.

BCMs and ECUs are designed with a certain amount of protection from faults, so there is a good chance they are OK and the fault is elsewhere.

If this is beyond what you are comfortable with, I suggest a specialist auto electrician which someone has personally recommended. Franchised dealers are often out of their depth when logical faultfinding is called for.

Following on from Austin 7 anyone that's been on the forum for a decent length of time will see posts where all sorts of strange electrical gremlins came down to a dodgy battery, usually one that's fairly elderly. (I experienced this myself). Before spending a lot of money I'd check the age of the battery - if it's getting long in the tooth think about replacing it now rather than when it fails (it's probably not that far into the future and in the big picture it's not a lot of money). Even if it turns out that replacing the battery doesn't cure the problem it's one critical thing eliminated and you can proceed with other tests knowing its a good battery.

1 hour ago, Paul52 said:

Following on from Austin 7 anyone that's been on the forum for a decent length of time will see posts where all sorts of strange electrical gremlins came down to a dodgy battery, usually one that's fairly elderly. (I experienced this myself). Before spending a lot of money I'd check the age of the battery - if it's getting long in the tooth think about replacing it now rather than when it fails (it's probably not that far into the future and in the big picture it's not a lot of money). Even if it turns out that replacing the battery doesn't cure the problem it's one critical thing eliminated and you can proceed with other tests knowing its a good battery.

^^^ But good to test the battery properly to confirm condition before replacing.

Simple enough to do while engine is being cranked-over.

My understanding is that TDIs are particularly sensitive to slow cranking speeds.

So on further investigation it has the wrong ignition switch fitted , 4 wire 1 plug , instead of the 6 wire two plugs , the other two wire plug has a diode taped into it under the steering column

Battery is good and fully charged , not able to do any other tests as i have no ignition , so cant crank or do any tests on draw on battery , i have ordered correct switch and will see

thanks graham

1 hour ago, DOZERMAN said:

So on further investigation it has the wrong ignition switch fitted , 4 wire 1 plug , instead of the 6 wire two plugs , the other two wire plug has a diode taped into it under the steering column

Battery is good and fully charged , not able to do any other tests as i have no ignition , so cant crank or do any tests on draw on battery , i have ordered correct switch and will see

thanks graham

Thanks for the update, please confirm success when correct switch fitted.

Do you know history of when present switch was fitted?

I'd suspect a diode to be there as an anti-flyback measure.

So fitted correct ignition , but second plug is not for the one i found with the diode in , fitted it and left second plug hanging . made no difference , fiddled around with fuses etc again , was giving up and tiding stuff away and saw the drl.s on , turned ignition with screwdriver and it started , used it for the last two weekends , then yesterday at the shop , nothing again , so still at a loss and may well give up on it , as time is not something i have plenty of