300tdi rev counter fail (ran out of ideas)

First of all Hi everyone. New to forum
My fiance owns a 300tdi on an N reg which I tend to be driving all the time as its the only thing I fit in essential piece of kit here in the sticks north of sheffield.
Ive recently fitted spots on the safari rack and then started having issues with the battery draining.

I realised i had also re plugged in the rear window heating element which I think has issues as it was possibly that causing the power drain.
I noticed that 2 days after fitting the lights (wired to after market spots on front via relay which have been on for donkeys) the rev counter had stopped working.
couple this with the power drain and heres me thinking loose wire or possibly broken alternator.
well after getting a new battery as old one bubbled over on trickle charge I then fitted and fired up the disco. all was well be no rev counter and it went flat again so disconnected the lights, it was then i found out it was the rear window element(something very dodgy about the amount of wires hanging out of the door at the back)
basically Ive checked the wires on the back of the Marelli (doesn't look like lucas. and even replaced the spade connector on the white wire to the W terminal.
Ive also ran a volt meter between the W terminal and the disconnected wire and got around 12 or something volts.(might be different now as battery is new) and Ive also started up the engine and unhooked the negative lead from the battery to check the alternator that way, it didn't stop.. also volts charging at 13.5-14.5 as in haynes manual
cant find any info via google any more than the usual check the spade connector and so on. I was hoping to get some help here. Will be grateful for any pointers.
all other lights and dials work on the dash. it wasn't erratic before it gave up as far as im aware, it just stopped.

Regards
Stu

Prob a dicky alternator. I have no rev counter either. Not like its needed to be fair

same here

Been looking at other posts n it sounds common. Turns out though that the heating element can't be draining the battery. Flat as a fart this morning so came to work on the bike. You don't think it's possible for the alternator to drain it over night if it's faulty? I'm beginning to clutch at straws now although it's true, it's not important to have a rev counter.
Thanks

Charge the battery fully - connect it up in the disco - leave it for a couple of hours - go out and feel the alternator - if its warm thats where your current is draining to

Daz

Teaman said:

... it was then i found out it was the rear window element(something very dodgy about the amount of wires hanging out of the door at the back)....

Click to expand...

I'd re-check all wire runs and that they're going to the correct places and are intact. I'd also check and re-check the alternator wiring and it's wiring insulation all the way ..

Sounds daft, but also check the handbrake cable! ... take it off to check it properly ... There were issues with them touching metal, wearing through the insulated covering and shorting other cables/chassis and causing all kinds of 'odd' electrical behaviour.

Sounds like the alternator is on it's way out, could be a load of things, but on this occasion I do think it is the alternator.

Do you have a multimeter? If not Maplins for a fiver.

Disconnect the positive clamp and put the black probe to it and the red probe to the battery terminal, put it on the 10amp setting, ensure EVERYTHING IS OFF, doors shut only bonnet open. Check the reading - note this down and report back.

Now press the bonnet switch down and lock the car.

Watch the meter, after a jump as it locks the car it will then sit at about 50-100mA before settling at about 30mA.

A little theory: 30mA = 0.03A, so it would take 33.33 hours to equate to 1Ah - so every week the vehicle sits unused it will equate to about 5.04Ah.

then re,enter your radio code...or yer radio wont work again

you really need to spend a bit more and get a clamp on meter with jaws that go round the wire to measure the current in it without dissconecting the battery.


this sort of thing but with dc amps... me teas ready
1000 Amp Clamp-on Multimeter AC/DC, Volts, Amps & Ohms | eBay

discomania said:

Sounds like the alternator is on it's way out, could be a load of things, but on this occasion I do think it is the alternator.

Do you have a multimeter? If not Maplins for a fiver.

Disconnect the positive clamp and put the black probe to it and the red probe to the battery terminal, put it on the 10amp setting, ensure EVERYTHING IS OFF, doors shut only bonnet open. Check the reading - note this down and report back.

Now press the bonnet switch down and lock the car.

Watch the meter, after a jump as it locks the car it will then sit at about 50-100mA before settling at about 30mA.

A little theory: 30mA = 0.03A, so it would take 33.33 hours to equate to 1Ah - so every week the vehicle sits unused it will equate to about 5.04Ah.

Click to expand...

Hi. I think ive done as you said.
Clicked the multimeter over to the 10A setting and moved the red lead into that socket on it..
disconnected the pos wire and got 3.22 reading? then when i did the switch/alarm button it spiked to 16.5 then back down to 3.22 and same when unlocking the disco.
Other things to note that whilst it was running i measured the volts between the W terminal and the spade on the white wire and it read 12.72 volts. the reading between the red pos cable off alternator and engine was 13.5 volts. still no rev counter and Id disconnected the relay for spots and also the rear window element. (just in case)
I then turned the engine off, disconnected the negative lead on the battery and between the terminals it read 12.28 volts. When i touched the neg cable to the battery the reading went down quickly to 12.19 volts and slowed down.
anything else?

just bought a second hand alternator off fleabay as well as a new waterpump, That squeeks anyway so Ill do both together.

Squeaking could be your belt tensioner
Try the "penny trick"

Daz

have heard reports of bad earths behind the dash causing erratic rev counter readings.
mine does it, the more load you put on, the higher the rev counter reads. bounces up to 6000 when heaters are on with the indicators.
re the heated rear screen, this is controlled by the mfu (multi function unit) in the drivers footwell. there are known cases where it will turn on the heated rear screen at random. (along with the foglights)
there is a test procedure where the mfu can be manually operated but i cant remember it. (tis on here somewhere)
summat to be going on with at least, will keep an eye on thread!

DEFENDER90-DAZ said:

Squeaking could be your belt tensioner
Try the "penny trick"

Daz

Click to expand...

oh teh pump has definitely died a death, its seals went ages ago and I needed the car so i helicoiled the hole it has in it, siliconed a cap head bolt n shoved it all back together.
alternator and pump arrived today at work so Saturday morning should be fun, I just hope its not raining.
before i take things apart ill do the 10a thingy again and disconnect wires from the alternator then do the fuses in turn.
the slow fault finding process

Afternoon. Just fitted the new Alternator (off ebay) and all appears to be well now including the rev counter being back up and working.
What I noticed was that before I took the old alternator off I hooked the volt meter to the battery and it read 11.95 volts. I then took the wires off the alternator and the reading shot up to 12.10 volts.
the second thing I noticed was the difference in size of the pully wheel on the alternator compared to the one I took off, the new one being genuine landy parts and the old being a 2 year old part Im more inclined to trust the size of the one I have on now.
Fitted a new water pump whilst I was at it and now with everything turned on inclusing the rear screen heater, stereo, alll lights, and what not it charges at 13.5 to 14.5 on tick over / a few more revs. Im happy at the moment and want to go out for a run
thanks for the advice peeps.
Stu

when I bought my 300tdi it had recently had new alternator. It all seemed to be wired up correctly. The spade connector for rev counter was plugged in etc.
on the alternator there was an unused bolt connection. I put the spade connector on there and rev counter worked.