I don't think they test anything but batteries, starters, alternators and ignition control modules, but I could be wrong.
I believe they can help with that
I think so
Yes most will if they want to sell you light bulbs or wiring
No they don't test trailer wiring. But they do sell voltage testers. So you can test it in parking lot.
Generally depends on the store and the team members individual knowledge. If they have a multimeter or even a test light in their toolbox, they should be able to check it. Try going later at night when they are less busy.
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