How far are you shooting? More zoom would be better here. I use the same camera out to about 70 feet which would be about top end of its range for this purpose.
Edit: Oh I see you are at 40 feet. Your zoom seems like it should be closer. Here is the same camera out to 70 feet.
View attachment 77214
See how dark that image is? Its ink black except for the plate and the tail lights. As mentioned, your images appear too grey.
Here is a daytime shot this morning. Sun is hitting the camera now so the image is a bit washed out during this time of the day:
View attachment 77215
Give me a bit and I'll post my settings.