charging issues

hey
I needed to check a few things behind the instrument cluster, so removed
it, fixed the wiper mechinism, then cleaned all the circuit board on the cluster.
replaced all bulbs, tighted all nuts, made new gasket to rest the amp nuts on
the installed the wires and tighten them tight... not over tight.
reinstalled the instrument cluster, started the car, amp guage read 40+
checed the battery while car was running, 18 + volts...
Turn off car, battery 13.7 volts..
these are not the same reading before I did any work on the car.
I've let the car sit at idle for about 5 min, no smoke\fire, took a small
drive around the nieghborhood, nothing wrong..
no smoke, no fire, but the amp reads high,
all connection from or to the battery are tight