Sounds like a problem with the generator/voltage regulator

Look for lose or brunt connections in the wiring.
also look for any nicked places in wires that might be touching frame ie this would be called a short or ground.
would be a good idea to put a battery tester on the battery,
sometimes batteries may act like the are fine but still can have internal shorts in the plates.
also like the other poster said generator/alternator, or voltage regulator may be bad. does it do it while cranking, or after. if it does during cranking check to see if the circuit runs thru the charger wiring bad starter can cause problems.
are there any switch in the circuit, if so check them. not sure if the ignition is in the circuit, or any switches that
you may have to turn on for instruments.

hope this helps

If it is the voltage regulator is it required that an AP mechanic change the part or is it something I can do on my own without any repurcussions at the next annual. Also how does one find an AP mechanic? The Cessna 150 airplane I have is located in Suffolk County, New York.
Thank you for the responses.

I'm not a pilot or a air craft mechanic, the suggestions that i gave are common basic electrical theory, i'm a industrial electrician but the rules apply across many different system and components. ac or dc electricity follows the least path of resistance.

i've thought about the voltage regulator and and was wondering if it was allowing high current/ amps wouldn't it affect other instruments that run under 20 amps

and as far a mechanic, i would think any thing that effects the flight controls or instruments would have to have a mechanic that is certified work on them.
i suggest you try the local small airports, if they don't have a mechanic on duty they might know where you can go.