Strange Ammeter Reading

[Deleted]

I have just driven 100 miles or so, on a motorway at motorway speeds. All went pretty well as usual (I am using the car as my daily driver and it has so far been very reliable) but I did get some worrying electrical readings. I was merrily bowling along when the ammeter suddenly shot from just above or around zero to about +40-50 (amps?!). At about the same time the radio seemed to suffer from some interference or other ( it still had the display so was still getting power but no sound). After a short while the ammeter shot back to a lowish negative reading and then to zero where it seemed to be stuck. I tried switching things on (lights HRW, the usual things which make it move) but it seemed to be dead. I also had the oil pressure warning light come on for a few seconds (even though the oil pressure guage was reading a perfectly decent oil pressure.) Back in town all seemed to be ok and the ammeter seems to be working fine and all seems well. I have never had anything like this before and I am sure something is wrong but I have no idea what. The above problems did not always correlate precisely with each other which made it all a bit more odd and disconcerting. I would be very grateful for any ideas as to what might be going wrong (I suspect the answer is going to be for me to take it an eauto electrician but as it is an intermittent fault I might have to take said electrician on a 100 mile round trip to convince him sonething is amiss! )

[Phil Nottingham]

A dead short is happening and the wiring/alternator needs checking out immediately. Is the plastic coated loam or the old fabric covered stuff?.

In the meantime fit a battery cut-out in a handy position

[Deleted]

Many thanks for the high speed reply Phil. I am having it looked at urgently. I suspect the radio wiring as it only seems to happen when the radio is on but the supply to the radio is fused so I don't know why the fuse has not gone if this theory is right (though thinking about it there are 2 supplies to the radio and only 1 fuse I know of). Either way I will get to the bottom of it before disaster strikes! Thanks again, John

[Deleted]

Check out the wiring loom under the nearside (left) rear door sill. It often frays there and can earth. The front one is less likely but still worth a look.

[Deleted]

Thanks (belatedly) for the very helpful suggestions. I have had it checked over and everything seems OK. I do not know if the checking process has helped but the problem has gone away even though no fault was found anywhere!

[dorsetflyer]

I would still be very wary of a future re-occurrence, and watch the Ammeter closely.
If the fault has not reappeared, it doesn't mean it's been cured.
In the checking process, it could well be that touching frayed wires were separated, and in time with vibration etc they will return to their normal position and reveal themselves again.