E30 Zone

I recently fitted new starter as old one was dying. After I fitted starter battery light and brake light were on, I've fitted a good alternator as thought that was issue but still 12v at lead when running , It's not earthing problem so now I'm lost as to what to look at next.

When running these are constantly on.

Disconnect the smaller (blue) wire to the alternator and measure the voltage between the D+ terminal that it was attached to and a good body earth (not an engine block earth)

Il get on it in the morning, thanks so much Brian.

It's got 1.52v mate and nothing at main lead

Now measure between the terminal and the alternator casing.

Finally got round to sorting the car and with a full battery it's showing 1.73 from the casing and the earth point mate.

If you have 1.73 volts between the alternator casing and the main earth point on the RH suspension turret, either the alternator isn't earthing to the engine, or the engine to body earth strap needs attention.

Thanks very much Brian, il get a new earth strap tomorrow and clean the contact points between alternator and block and see what it does

Managed to get half an hour to go swear at it again mate, connected jump lead from battery neg directly to alternator casing and no difference and tried on block etc to no avail.
I tried different points along the blue wire along engine loom and made no difference it was same voltage 1.73.
I tried batt pos direct to D+ and it made engine run different so took it back off.
When I removed old alternator the D+ post had became loose and batt light would come on intermittent and my starter was turning slow so decided to replace them both, think I'm going to have to check all wiring this weekend it's doing my head in now and I'm crap with electrics

Been messing with it again, with ignition on and exciter wire disconnected from alt it shows 12v and same when running but if you reconnect it it drops back to 1.73.
My old alternator was a valeo but new one is bosch, old one charged ok but terminal was loose. I've just fitted new brush pack and voltage regulator in new one to see if that will sort it.

Just the same, thing is driving me mental now

johnmaccow wrote: ↑

Mon Apr 12, 2021 5:32 pm

I recently fitted new starter as old one was dying. After I fitted starter battery light and brake light were on, I've fitted a good alternator as thought that was issue but still 12v at lead when running , It's not earthing problem so now I'm lost as to what to look at next.

You say this started after fitting the starter motor?? Especially as you say there is 0 volts at the alternater main lead.
Have you checked the starter motor connection main power supply? there is a link wire from the starter motor to the alternator, if you have left this off there will be no main battery power connection to the alternator.

Yeah it's on mate and I've checked connections and and all good. It starts fine and alt thick red lead is same voltage as battery. I've done a bit more searching and apparently a lead from starter that interrupts power supply to other things when starting the car so going to try to look into that next.

I you put a positive to the D+ terminal with the alternator turning it should then start charging, best to have it connected to the battery and measure between alternator casing (earth) and + terminal on alternator (positive) this is effectively bench testing the alternator, you can do do this with it in a vice and use a drill chuck in the belt to turn it, or just run the engine

Thanks Dan, I think I've replaced a bad valeo alternator with a knackered bosch one, I replaced brush pack and regulator and ran 12v to d+ and alternator got hot really quick so think it's an internal fault and had 7v at d+ terminal.
I've got another valeo to try, failing that il buy a new one or get one refurbished.
If I take the d+ lead off the lights on dash go out , d+ lead is producing 12v batt voltage.
Separate topic but probably getting rid of the m54b30 lump if you know anyone looking for one Dan.

Managed to get hold of another valeo cheap and remove the part that was broken where the d+ attaches by heating up the solder and swap it for my broken part on my original one and it's working fine again. No idea why it didn't like bosch ones but there you go