Bad ground? Please help!

[plrs x45]

Thank you all in advance. This is a great website for X's. I believe I have a bad ground and do not know where to start. The right turn signal stopped working and just makes a buzzing noise. The left works fine. When I hook up my boat or jet-ski's and plug in the lights, the right turn signal works. On my vacation in July, I got a flat and when we were changing it, the spare is live (flowing electricity). Is there a first place to look? Where do I start?

 

[Howard]

To test it all out. Remove the rear light cluster and the plug to the indicator and use either a voltmeter or test light. (a 12v bulb with two pieces of wire). Check for both power and earth. Don't forget to check the lamp also. If the rear is all ok then check the front the same way.