Welcome to Tom's Hardware, @jb3218!
Unfortunately, I'm afraid that @greens is totally right on this one! You will need to re-format the WD My Passport external in exFAT or FAT32 in order to be able to use it in the vehicle. In order to do that you should back up any data that you might have already stored on the external HDD and copy it safely to your computer. The reformatting procedure will erase all the data you have currently stored on the drive. Here is a helpful tutorial from our knowledge base about
Formatting a WD drive in exFAT or FAT32.
I'd also suggest you read through some of
File & Partition size limitations that come with teh FAT32 file system.
Make sure you always back up your files from the WD...