New alternator causing electrical buzz

[Ginothy]

I seem to remember the battery light flickering on and off when I last took the van for a spin. Will check it again as soon as I'm dressed and up...

[Ginothy]

ok, I've checked the dash battery light and it isn't coming on so I'm assuming it's ok to connect the blue wire to the bolt fixing on the alternator as seen in the picture posted last night?

As for the buzzer

The flashing oil pressure light and 'buzzer of doom' are operated by the low-low pressure switch, hence at lower engine speeds.

So it's the low-low pressure switch that is setting off the buzzer, i.e. it will only go off at low rev's if there's a problem? I don't have a rev counter so can't see what revs the buzzer is going off at but they're certainly high, hence it has little to do with oil pressure? How does the sensor switch circuitry differ at higher revs, if at all, without a rev counter or is this beside the point?

I'll try and search out those connection points for the sensors and see if I can decipher if there's a problem there.

[Mocki]

yes, blue wire needs connecting

if the BoD comes on at more than tickover is may well be a connection disturbed by the changing of the alternator,
as the BoD senses revs by the "W" connection

remove the wire going to the "W" connection and it should shut up, but that wont help you find if it is real BoD of a wiring issue

so either check oil pressure or check wiring.

[ghost123uk]

Oh dear, this is getting overly complicated

Firstly

The flashing oil pressure light and 'buzzer of doom' are operated by the low-low pressure switch, hence at lower engine speeds.

Is incorrect, a signal sent from the high pressure sensor will also set off the BOD (pretty obvious design feature isn't it)

so,

As for the buzzer...
So it's the low-low pressure switch that is setting off the buzzer, i.e. it will only go off at low rev's if there's a problem?

Is also incorrect

And...

ok, I've checked the dash battery light and it isn't coming on so I'm assuming it's ok to connect the blue wire to the bolt fixing on the alternator as seen in the picture posted last night?

If the battery light is working correctly (I take it you know what it should do, same as on any other car) then I cannot explain that, as without the blue wire on the alternator, it simply should NOT be working !!

How does the sensor switch circuitry differ at higher revs, if at all, without a rev counter or is this beside the point?

Yes it is beside the point, there is still a wire going to the dash that has the RPM data on it, rev counter fitted or not. These signals also feed the BOD circuit to tell it when ~2000 rpm has been reached. This wire, ONLY ON A DIESEL comes from the "W" terminal on the alternator and I think is red with a black stripe, or is it the other way round, I will check !

For future reference, on a PETROL engine the RPM data is sent from a wire on the coil to up front. According to Heynes it is coloured Green, but I will check the "real world" to confirm shortly

Edits = just tidying up the post.

[Ginothy]

Ok, sorry for confusing the point! Thinking too much. Battery light does not work so will connect the wire.

[ghost123uk]

Ok, sorry for confusing the point! Thinking too much.

No worries Tim, we will get there

Battery light does not work so will connect the wire.

Ah got ya, I thought you meant it was not coming on when the engine was running (as in, indicating a fault) as opposed to not coming on at all.

You have to wonder why the previous owner disconnected the blue wire ?
You may be about to find out !

p.s. = That blue wire is the one that is usually also used on a camper to switch the split charge relay on and off.

[Mocki]

John, you just made me read the whole thread again...... !!!!
no mention of PO the issue occured due to replacing alternator by CO

we seem to have got off track a bit here .........

back to basics.

alternator needs connections making correctly before we try and sort the BoD thing, as it maybe all down to wires wrong at alternator anyway???

[ghost123uk]

John, you just made me read the whole thread again...... !!!!
no mention of PO the issue occured due to replacing alternator by CO

True, but I guessed the CO was not the one to terminate the blue wire
Note = I ain't going to read it all again to check that

alternator needs connections making correctly before we try and sort the BoD thing, as it maybe all down to wires wrong at alternator anyway???

Agreed

[Ginothy]

Ok, alternator now wired up correctly (I hope!). Oil pressure lead into the W terminal, big fat red + lead from the battery wired up as my old alternator. Blue battery indication light lead into the only other available position. Dashboard battery light works, buzzer now comes on at low revs (?! I'm not making this up just to confuse you I promise).

Feel free to ignore this next bit if it's irrelevant: My dip stick told me oil was extremely low a while ago so I topped it up until half way between the max and min points on the dip stick. Having run the engine for a while now it's saying I've got way too much in there. Seems like a straightforward answer to what's causing the buzzer to go off? Will drain some oil tomorrow, I have a date with a game of rounders for now...

[ghost123uk]

Having run the engine for a while now it's saying I've got way too much in there. Seems like a straightforward answer to what's causing the buzzer to go off? Will drain some oil tomorrow,

Aye, drain it off till correct, remember to be on level ground !

Although I read somewhere that over filling can cause oil frothing, causing air bubbles, hence low pressure and bubbles, personally I have not come across it. Lets see

[Mocki]

i am NOT convinced that wire on the "W" is the correct wire some how.....

just putting the charge indicator wire on shouldn't have made any difference to the BoD

something more going on here methinks.
you need to check the connection to the oil sender on the engine, AND the oil level and pressure

[ghost123uk]

i am NOT convinced that wire on the "W" is the correct wire some how.....

Umm, mine is petrol, so that is what I "know", I got the "W" wire information from a quick(ish) bit of searching on here etc =

Unverified stuff at http://volkswagenownersclub.com/vw/arch ... 941ab1e03f" onclick="window.open(this.href);return false; = I finally discovered where the RPM signal for the oil pressure system comes from - the W terminal on the diesel alternator. More good stuff at = http://reflectionsandshadows.com/cabby/dopws.html" onclick="window.open(this.href);return false; (though not directly related to T25's but explains the principals well). and = "hi, W terminal on an alternator is signal to tacho" from Brickerks (the rough n tumble T25 Diesel enthusiasts place) at = http://www.brick-yard.co.uk/forum/w-ter ... 37580.html" onclick="window.open(this.href);return false;

I'm getting carried away here - packing it in for now and goin t pub

Worth the OP checking up on this for sure, or the input of someone who knows for sure might help here.

just putting the charge indicator wire on shouldn't have made any difference to the BoD

[and]

you need to check the connection to the oil sender on the engine, AND the oil level and pressure

We concur

[Ginothy]

Right well, I managed to work out where the oil pressure switches were (thanks to your help) and there was indeed a broken length of wire. Most likely caused when I replaced the starter motor as I did that just before I replaced the alternator. Buzzer must have kept quite after that repair as the alternator was buggered?

It was the high-low pressure switch coming from the top of the oil filter that was broken.

The oil levels were fine and didn't need to drain any off. That was just me being paranoid/ stupid and checking the dip stick at a couple of mins after I had stopped the engine.

So in short, you were all on the money from the start and I shouldn't have gotten so worked up about it. Though I'm still not sure why the buzzer was going off at low revs yesterday, I haven't checked the oil pressure yet as I'll need to hire the equipment for that. Finger's crossed I won't need to and that the problem is now resolved.

[Mocki]

thanks for letting us know, its good to hear the end result, sadly so many never bother to close the chapter which leaves the questions hanging for those searching in the future with the same problems!!!!!

Hopefully you have learnt something from this as well, which can be passed on in time to come to others !

thanks

[Ginothy]

No worries, advice I got from all was very helpful. Especially from Steve and John, I owe you both a pint!