High amps reading

[jakej]

We have a B&C 40 amp Alternator fitted to an IO-360 & D120.  Since first engine run the ammeter shows a fluctuating high (+5 up to +36) amps output however volts are always stable at 14.1- 14.2.  Turning on 'loads' exacerbates the reading - any thoughts on why this is happening ?  Shunt is in position "B".  

 

[jakej]

More info from owner/builder -

Initially Ammeter was showing +5 to +13 Amps no load and +15 to +26 under load ( Nav & Strobe lts on)

last 2 engine hours it is showing +13 to +25 no load & +15 to +26 under load.

 

[dynonsupport]

Generically, this may be a grounding problem. The shunt is 1 millivolt/amp, so those could be fluctuations of about a tenth of a volt. When the engine is off, does the ammeter zero out?

 

[jakej]

I'll see the plane in a few days time - will report back