It is unlikely that normal systems in the car are drawing enough current to flatten your battery (although not impossible). As Grant said to flatten a battery in 4 days would require about 1amp continuous.

I would be looking for a light not turning off maybe the boot. If all the lights are off, then you can systematically remove fuses to isolate what circuit is drawing too much current.

Remove the + battery terminal and insert your meter on AMPS range (most meters have 2 inputs 400ma and 10amp DO NOT use the 400ma you will blow the fuse).

Attach the + to the battery + terminal and the - to the battery cable (DO NOT START THE CAR WITH THE METER IN THE CIRCUIT YOU WILL BLOW THE METER FUSE).

 

is there any reason why the 115a alternator is favoured more than the later
120a unit when upgrading the charging systems on the v12 ?

 

Nope.

When I did mine 10+ years ago the Bosch 115 was all I could get, so it was a no brainer as they say.

If this upgrade was not as easy as it was, or as readily available as it was, I would have fitted a second alternator where the air pump should have been (we no got air pumps), and called it a day.

So, really it is your choice, and I suppose the bigger the better, BUT, that "V" belt will have issues driving any more than 100ish amps. Then the infamous rubber vulcanising of the pulley on the crankshaft that actually drives the alternator comes into the equation. I ask, HOW GOOD is your pulley rubber bit??. Mine was toast, so had it re-vulcanised at the same time.

 

Well,


I have been having the same problem with my 90 conv. I could not get access to the braided cable connecting the engine pan to the suspension subframe, so I ran a 19" 6AWG cable from the R/H cam cover to the inside of the wheel well. I also cleaned all ground connections in the trunk.


Thought it was solved, but still had intermittent charge with indicator reading at bottom of 13. The battery warning light came on when key turned on, but engine off as described in this thread.


I pulled the instrument cluster, changed the battery warning bulb and also cleaned all contacts on the printed circuit where the two connector plugs plug in and applied bulb grease. New battery reads 13.48 v engine off. With engine running voltage is 14.10 to 14.68, so I think the cleaning of all contacts for the instrument cluster solved the exciter problem.


I am going to continue to carry a spare battery and jumper cables for a while until I am sure. I still do not trust the load dump module for the Bosch alternator. I am trying to locate one in a salvage yard since it does not seem to be available new.

 

hahah voltage gauge. I have to give mine a sharp tap at startup for it to pop up and read anything. It has been useful before, but i think we pretty much need to build an aftermarket instrument cluster inside the glove box to reference sometimes.

I am mostly suspicious of the craptastic flexible circuit board on the back of the cluster