C3 electrical problem - multimeter readings
 

OK, I have taken Warrens advice and connected up the multimeter inside the car and got a passenger to take down some numbers. I connected the multimeter to the radio wires as my car has no radio (wouldn't be able to hear it anyway).

Just to recap; the car is a 77 Carrera 3.0 and my battery is not getting charged. It has a new volt regulator, the alternator was out six months ago and was sent for testing, (it was replaced by the PO six years ago) I checked all the fuses, my ignition switch is worn and needs replacing, also I took the fuse out for the full beam as I was unable to switch them off, I suspect because of a worn indicator stalk.

The big engine/body earth strap is brand new, the battery is six months old, posts are clean etc. It ran down but but has since been on a trickle charger and now reads 12.66 when the engine is off.

When the car is parked I disconnect the battery via a device on one of the battery posts as a kind of theft deterent/battery saver.

When i start the car the voltage drops to 9 ish then goes back up to (fluctuates) 12.25/12.42

at 1000 rpm it is approximately 12.58

at 2000 rpm it is approximately 12.63

at 3000 rpm it is approximately 12.62

at 4000 rpm it is approximately 12.59

at 5000 rpm it is approximately 12.59

at 6000 rpm it is approximately 12.55

at 7000 rpm it is approximately 12.55

this was done in 2nd gear (road wasn't long enough for third gear)

with the lights on it drops down to 2.85

there are smaller drops with the wipers, indicators on etc

I drove the car around for about an hour and the meter reading was quite stable around 12.39/12.38 whilst driving but dropped to 12.25 ish when idling at some traffic lights for example.

any thoughts anyone?

regards

Andrew

77 Carrera 3.0

I'd recommend connecting the multimeter closer to the battery posts as your current connections to the radio wires may be measuring available voltage after another load in the radio circuit (I don't know); i.e. not a true indication of source voltage.

If a connection directly to the battery gives you identical numbers, it appears the charging system is not doing much. If you operate your car for any length of time the batttery will probably go dead; less time if your headlights and other accessories are ON. Does your charge indicator light go ON with the ignition ON then go OFF when running? BTW, a fully charged battery should be around 13.2 volts.

With the engine running, you should be in the range of around 14.4 volts with accessories ON, so I would suspect a faulty alternator or regulator (I know, it's new). Check all grounds and connections first before buying new parts. How about the trans. ground strap? A good electrical shop with the wiring diagram should be able to diagnose this one.

Hope this helps a little,
Sherwood Lee
http://members.rennlist.org/911pcars