It's not the light, overcast "diffused light" is actually better than harsh direct sunlight. The problem is that objects reflect color, in this case grey. Red is such a vibrant color and the greys (from the clouds) reflecting off the surfaces washes out the color.
If you want a great photo shoot, grab a tripod and shoot 30 min before sunset. Also, use the cloudy setting on your white balance or custom with a grey card. Good start though. Composition is good. Next time shoot from perpectives you normally don't see. Also, don't try to capture everything in one picture. You want to show the car off, not sell it on Ebay
Take a few steps back and zoom in on details.