Voltmeter malfunction?

[droptop]

Over the last few months, I've noticed the voltmeter on my series 1 spyder starting to read on the low side falling almost to the red zone when I'm driving with lights, wipers, etc. on.
Now the thing is that the battery is charging fine and the alternator is putting out around 13-13.5 volts with all lights on indicating that it's healthy.
Also, the panel lights dim noticably when the lights are switched to main beam.
I suspect a bad connection from the alternator to the fuseboard but where do I find the connection on the board to run a new heavier cable?
Currently, the circuit from the alternator consists of a short 10 sq.mm link form the alternator to the starter solenoid with the heavy battery cable completing the charging circuit, and a lighter, maybe 4 or 6 sq.mm cable from the alternator presumably going to the fuseboard.
The wiring diagram in my Haynes manual shows the wiring to be slightly different, but as these seem to be generic diagrams, I'm not too concerned and I have to factor in that the wiring has been repaired albeit rather poorly, by the previous owner.
All battery cables are new as is the charging circuit ilnk.
Originally, when I got the car, the needle on the voltmeter stayed about 3/4 way over to the right with a slight swing towards the low side with all electrics on.
My biggest concern is that if the alternator does die, I won't really know in time as the charging light doesn't always illuminate if a fault develops like for instance, worn or broken brushes.

[peteracs]

Hi

Before you go ahead and replace any wiring, can I suggest you measure the voltage across the voltmeter, the voltmeter to the -ve on the battery and +ve to the +ve on the voltmeter and, assuming it is a poor connection, where the loss in voltage is occurring. This should give you a better view on what needs addressing as it could so easily be on the ground side rather than on the supply side where the high resistance is occurring.

Peter
 

[droptop]

Thanks Peter.
I tend to overlook the fact that these cars seem to have ground issues and it could indeed be down to the ground to the instrument cluster.
That would also explain the dimming of the panel lights with the increased load from the main beams.
I'll start there and see where that leads to.
I have to remove the cluster anyawy to check out a fault in the oil temperature gauge which goes to "Hot" within ten minutes of the car satrting despite there being a good sender and the temperature is obviously not rising to this level or the engine would be fried by now.
I'm having a quiet spell work-wise and as usual it's raining here so what better time to head out to the "lab" with a gallon of cofee and a box of good intentions?

[VXdeMayo]

Hi, I would also agree with Peter, I would check the earthing wires / terminals ect first, as they can cause a lot of intermittent problems!
Best of luck.
Chas.

[peteracs]

Thanks Peter.
I tend to overlook the fact that these cars seem to have ground issues and it could indeed be down to the ground to the instrument cluster.
That would also explain the dimming of the panel lights with the increased load from the main beams.

The dimming could just be due to the extra current being drawn by the main beam lamp, and having a poor earth/bad connection on the instrument cluster would explain that.

Best of luck!

Peter