parasitic battery drain

OK Rani, your "little red meter" is able to measure 10 amps, the Radio Shack as much as 30 amps

In the top right of that "little red" meter, the "green" section is "DCA" means "Direct Current Amps"

The smallest scale is 200 micro amps, and the largest is only 200 ma or milli amps. That is .2 amps, or 2 /10 of one amp. Not very much -- probably about what it takes to light your test lamp

BUT at the bottom right see the red bracketed setting which says "10A" You want to set your knob there, plug one probe into the "com" which means "common" and plug the other probe into the "10A" top jack. This will give you up to 10 amps of reading, so you start with that and see what you have

Now look at the RS meter..........

With the bottom knob set on the DC ma, you go by the brownish box on the upper knob, so the scales available are 3ma (milli amp), 30, and 300 ma (300 milli amp) which is only 100 ma larger than your red meter. These measurements are taken with the probes in the two right hand jacks

BUT notice that the top knob, all the way CCW, says 30A. That is 30 AMPS which is nearly as much as your factory A body dash ammeter can measure!!!

BUT..........

You must be very careful to get the two knobs properly set for 30 amp, IE the top knob at the 30A, and the bottom knob at "DC ma" AND THEN plug your probes into the LEFT two jacks on the meter, IE the far left being marked "30A"

Since you are "experimenting" I would try both meters and see what they say, then post back. If either reads more than 200ma or .2A then that is the limit of the smaller scales on the red meter. If either reads more than 300 or .3A then that is above the limit of the RS meter on the smaller scales.

By the way, my first digital meter I ever owned was that very model RS meter. Later I bought a much -hated B&K, until I found that Fluke worked so much better.

EDIT WARNING Be careful that when you have any meter set up for current readings that you do NOT connect the meter from a power source to "ground". Also attempt to determine if the current reading you wish to take is within range of the meter. This is why I suggest using a test lamp first, as you can get "some idea" of the current involved. If a large heavy lamp such as a dome, stop or tail lamp lights dimly, you don't have very heavy current there. With the same circuit, a "smaller" test lamp will light more brightly. But if a small test lamp lights fairly dimly as well, you can be assured there is not a large current flow. Most probably LESS (safe) that the 10A reading of your "little red" meter