I had a minor collision which damaged the left rear of my car. Part of the rear fender where the lights are had to be panel-beaten back to shape, resprayed inside and out and eventually fitted with a new tail lamp which I bought. Now, the left light is less bright than the right one and the bodyshop blames it on the quality of lamp I bought. But the supplier insists it is a genuine part and not an imitation. What could be the problem?

If the tail lamp unit is a good one, there is no reason for it to produce a lower level of illumination. In fact, even if the lamp unit was not a genuine part, there should not be any difference compared with the original in terms of brightness.

You could check to see if the bulbs are of the same wattage. Try swapping for a new bulb.

Most likely, the reason for dim lights is a bad earthing point. The interesting aspect of automotive electrics is that the negative terminal is connected directly to the chassis and engine.

Hence, for any component that is powered, the negative can be fed directly from any metal panel near the device. There is therefore no need to run wires all the way from the negative battery-terminal to the individual components.

But the negative wire must be tightly bolted or screwed on to a metal surface that is not insulated by paint.

In your case, it is possible that the bodyshop had sprayed over the original connection point and hence reduced the conductivity of the earthing link.

Removing the connection and scraping off the paint to bare metal, then applying a little grease before re-connecting the wire will most likely solve the problem.

In many lamp assemblies, the negative wire may not even exist as the mounting screws act as the earth link between lamp housing and bodywork. Paint on the screw sockets will also diminish earthing conductivity.

Shreejit Changaroth