Here are a few testers that while not good enough for serious troubleshooting, will give you a good idea if you do have a problem then you can dig deeper into any problem you might have.
LtoR Meter I bought at radio
shack, as accurate as my Fluke and a lot cheaper, tester for 120vac (US) circuits, indicates with leds if any problems, this one also checks GFCI for proper operation, next two are for checking 120 vac but do not have GFCI test, Next one is for checking battery
charge level, alternator
working or not and shows voltage on digital meter, Last one is homemade version of next pix, this is an adapter for any clamp on amp meter, the coils in the black lead are ten turns and they will multiple your reading by 10, good for measuring low ac currents, you can make it cheaper that the one you buy.
This is the commercial
adapter for reading low ac current
and is available for most clamp on meters. mine (homemade) is as good and cheaper.
This is a heavy plug
in adapter for 12 volt stuff, heavy and fused may be used for several elect items at same time if needed, from radio
shack. I use this for my mobile ham radio 2 meter xceiver.
Closeup of digital/led tester for 12 volt dc lighter plug
, this is great for a quick check of alternator
output and battery
These are not expensive and easily obtained and will give you an instant idea if you really have a serious problem so you can troubleshoot more if needed.