A high-output alternator can supply 100 amps or more to the battery immediately after starting, so pegging a 25-amp ammeter is not only possible, it's very likely, even if the accessories are wired to the downstream side of the meter. Shunt the heavy charge current enough to keep from damaging the meter, if you want to keep the dash looking original.
Jerry
That's exactly why I put a shunt across the ammeter on my '50 pickup. When I bought my truck at a show at the Hershey fall show several years ago, the truck was fitted with a 10SI alternator and the gauge was pegged on the charge side. A quick check with a clamp on meter showed that the alternator was pushing out 60A for a few moments immediately after starting if the motor had cranked for any length of time. The alternator still does this, but with the shunt in place, the needle kicks over, but doesn't peg. There's some more detail
here -scroll down the page once you've clicked the link.
Stuart.
