Porsche Enthusiasts Club Forum

s'pose to be setting off to nurburgring tommorow evening, just set off out in car and noticed voltmeter on dash only reading 12v instead of usual 14v.
Ive dropped multimeter on battery with engine running and got 12.3v
12.5v with engine off.
put meter on back of alternator, positive lead on to big connection in centre and negative to smaller connection and with engine running got 12.3v.
switch off engine and i get zero volts.

I think this sounds like alternator so my weekend trip to ring isnt going to happen.
80110ck5 !

Any thing else i could check?

Martin, try pos to the big terminal on the alternator & the neg to ground close or on the alternator. But yes it sounds like a knackered alternator. Is the warning light doing what it should? e.g. on when ignition on & off when engine running? Where are you? I have a spare 944 S2 one here in Kent?

Try it with the meter Pos to the large terminal and the and the neg to earth.
The small wire is for the warning light.

Also try it across the battrey and then turn the lights, heater and HRW on

Jim he is in Nottinghamshire

Battery light doesnt come on with ignition on or engine started, but cant say ive ever noticed it before. but voltmeter drops when lights are turned on with engine running.

Just seems strange its still giving 12 v from alternator usually they pack up and give nothing out, dont they?

By the way im in Notts, but thanks for offer off alternator.

Martin, I have an alternator here & I'm around all day tomorrow. If you are going by ferry then dropping off here is 10mins off the M2. My alternator is on an S2 & is believed good, I'd suspect the 968 one is the same but don't have 968 parts manuals. If you can get here quite willing to change it, or we have a big alternator recon place 20minutes away.

Battery light should come on, has the bulb blown? If it has it shouldn't affect the charge but may do.

Do the lights brighten up when you blip the throttle?

If the warning light is not working it will not charge.

Try earthing the small wire on the alternator (blue?)

Martin, I have an alternator here & I'm around all day tomorrow. If you are going by ferry then dropping off here is 10mins off the M2. My alternator is on an S2 & is believed good, I'd suspect the 968 one is the same but don't have 968 parts manuals. If you can get here quite willing to change it, or we have a big alternator recon place 20minutes away.

The plan was to get down to dover thursday eve and book in hotel over night, then get 6.00 am ferry across.

Ill try and get it diagnosed tommorow by auto electrician, but its a bit risky driving all the way down with a dodgy alternator, thanks anyway, do you have a contact i can get you on just in case ?

Battery light should come on, has the bulb blown? If it has it shouldn't affect the charge but may do.
( dont know but never noticed)

Do the lights brighten up when you blip the throttle?
( no )

My replies are a bit out of sync, slow at typing!

Martin I'll PM it. I'm on leave this week but have to be in the office Friday & off to the USA at sparrows on Saturday.

A blown ignition light bulb will stop it from charging. But it is very rare for the bulb to blow.

Earthing out the warning light wire on the alternator will test this.

Just run that by me again.

If the alternator warning light bulb has blown it wont charge?

And when you say earth out the warning light wire you mean remove it and earth against body? If light is working should this cause it to illuminate?

Yes & yes

If you earth it out and it works then it means that the diodes in the alternator are knacked

Right, ill have a look in morning

All the best
Mart.