Taillight issue

Measuring voltage with a volt meter can show battery voltage where there is a really bad connection in the path.

Get a tail light bulb and add a wire to the base and to one of the contact points. A bulb socket makes this easier


Then put it in the cir like if it was the volt meter. If the light doesn't light then it indicates a bad connection,

They make test lights that do the same but a bulb and wires work in a pinch