Electrical Troubleshooting

[Harley Babeu]

I need a little help troubleshooting a battery drain problem.  The battery
is being drained overnight.  As a short term solution I am disconnecting
the battery when it sits for more than a few minutes.  The car is an 87
5kcstq.  The alternator was replaced about 6 months ago and the battery
about a month ago.  I believe what I need to do is measure the current
drain on the battery with the car off and start disconnecting fuses to
isolate the circuit that is still on and then trace it until I find the
problem.  Do I need an ammeter for this (and if so who makes a reasonably
priced and decent quality one) or is there someway of doing this with a
test light setup.  I seem to remember reading something about doing this
with a light but cannot remember any details.  Please help with any
suggestions on the easiest/quickest/cheapest method of troubleshooting this.

Thanks
Harley