Unsteady and high voltage

[markymark]

Hi All,
I have a problem with the charging on my P5B coupe. The ammeter waves from positive to negative and back continuously after a few minutes of running. The charging warning light flashes on and off too.
Measuring the voltage on the battery with engine running and no electrical load, I can see a voltage that is constantly changing. It ranges from about 13V to 15v+.
Before I measured the voltage, I suspected the brushes. Alternator is the original 11AC type. I ended up fitting new brushes and slip ring. The problem continued so here we are.
Could it be that the 4TR is faulty?
Anything else to suspect?

All suggestions welcomed.
Thanks,
Mark

[Phil Nottingham]

It could be the 4TR, the 3AW or just poor connections especially plugs and earths

 

[p5andrew]

If it were me, I would definitely start by making a thorough check of all connections throughout the system, both for cleanliness and tightness.  Do not forget to check the earth straps from body to subframe and to the engine.  All mating surfaces need to be bright and clean.  Doing all this will cost you time, certainly, but nothing more.  If the fault is cured, great!  If not, attention will then need to turn to the 4TR and 3AW.  As I expect you know, with all lights/heater fans etc turned off, an 11AC alternator charging system in good condition should give you about 14.4V with the engine running at around 1500RPM and the voltage should be stable.

[markymark]

Thanks both. Good advice. Will advise on progress.

[markymark]

Hi All,
An update:-
I have been through the wiring end to end and cleaned up all connectors.
I have removed and refitted the earth cables at battery end and engine end. All now connected to bright clean steel.
I have had the alternator bench tested by a specialist. He says it’s working fine.
I have changed the 4TR with a new unit from JRW.

And still the problem persists.

Not sure where to go next with this. Any thoughts welcomed!

Thanks,
Mark

[percy]

I would have avoided the 4TR supplied which looks like a piece of "Chinesium" to me. A genuine NOS Lucas would have been the way to go.

[Phil Nottingham]

Did you check the bunch of earth rings on the inner wing near the bonnet hinge? Also check the busbar under the dash near the steering column. This has the man battery and charging leads and can suffer from screen  and bulkhead leads