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electrical fault

To keep it simple, ign on: fuel gauge moves and stops at the correct level as per what is in the tank, also I have a electrical water temp gauge and all ok. When the vehicle is running (daytime) the voltmeter on the car shows about 14.2v so all ok.
I also have an solid state voltage stabilizer which reads 9.8v.

Now when driving put on the headlights and or fan motor heater on; the voltmeter (meter) drops to 12v, the voltage stabilize drops to 7.2v ish the water temp and fuel gauge move up the scale by a fair amount ie am I over heating (no) and great fuel consumption!! (no).
As the problem lies with the engine running I changed the alternator today, very little change to the instruments ie the fault is still there, although a slight increase in voltage ie new alternator.
So, where do I go from here? a bleed to earth in the wiring which drags down the volts but the alternator fights this and hence the voltmeter shows enough just keeps the system operating but, why does the voltage stabilizer drop down when it has 12v available!
Help.

Cheers Mick G

Re: electrical fault

I'm not an electrical engineer….just to be clear !

To reduce the work involved, take the battery of and charge it overnight, then start the car, put the fan on - does the voltage drop ? - if so clean all the connections from battery to fan, repeat for both headlamps.

If you have kept the original MGB wiring loom I would be looking at the crappy Lucas bullet connectors for corrosion, and then look at the quality of you earth cables to ensure they are good.

In summary, I think you probably have a dying battery or some really corroded connections.

Malc

Re: electrical fault

Thanks for your guidance Malc however solved the problem while looking at the engine earth strap!
About five years ago I changed the engine and since then this problem arose not long after and accepted it; at the time thinking of the problem I changed the voltage stabilize to a modern solid state type, did it stop the temperature going up with the fan heater switch on; no but at least I new the engine wasn't over heating.
I fitted another engine in January as the other had a rear crank oil seal.

So, twice I've fitted an engine and never notice on both occasions I hadn't re connected the wiring loom bundle of earth cables which I had neatly tucked under the chassis strut next to the engine mount earth strap!

Plonker comes to mind Rodney!

So, all instruments working fine and the headlamps are brighter as the volts are up.