BMW E30 alternator/power drain

[TROOPER88]

Hello
I posted on here with a great response a few weeks ago regarding my new purchase; an E30 325i Convertible.

I have managed to sort most problems and have now strated to investigate what the previous owner called a 'slow battry drain'.

Ok; I collected the car and used it for a week or so with no problems. I then tried starting it on the weekend and it would not start; just the 'clicking/ticking' noise. Today I purchased a multimeter having never used one before but am happy to learn!

I tried the multimeter on my other car and on my partners BMW. Set it to 20v and put the black end on the negative and the red on the positive terminal of the battery. Both came gave similar results of 12.5 volts with engine off and 14.5 volts with engine running.

So now I turned my attention to the 325i; with the car as it was (apparant flat battery) I had a result of about 11.3v. I was surpsied by this as I thought it would be much less if it was flat? Any way 11.3 volts and it would not even turn over.
I put the booster pack on to get the car running and got a maximum of 13.32v (this was after a long motorway run).

I then switched the battery from the 325i into our other BMW to try and remove the battery from the problem. It worked; 12.35 off and 14.06 running.

I am now unsure where to go? I guess the alternator is at fault as should it be getting the output upto 14+ volts with the car running; is this correct?

But even if I replace the alternator it is not going to prevent/stop a battery drain.....

I did unbolt and remove the aftermarket amp connection form the positive terminal. With this amp terminal now hanging loose I tried the multimeter with the black on the negative and the red on the amp terminal and was getting a reading of 0.9 volts. What does this mean; that it was draining this amount or that it needs that amount to run?

My electrics knowledge is extremely poor.


Any advice would be great.