First, those are not Iron Cars, they're Scrap Cars. Basin & Range. A file called SDSIndustries0.FPK is needed in CustomAssets. Ive included it in a Zip in case you don't have it.
One of the first things you need to do, if you haven't already, is download and install the maps required for mapping if using Mods. (See the first Sticky under Maps) There is a thread I wrote on map making under Talk also.
This is what your Scrap metal in Goods should look like:
<Good>
<szName>Scrap Metal</szName>
<szClass>Freight</szClass>
<szGTMLIcon>icon_scrapmetal_32.tga</szGTMLIcon>
<BitmapLarge>
<szFile>icon_scrapmetal_64.tga</szFile>
</BitmapLarge>
<BitmapSmall>
<szFile>icon_scrapmetal_32.tga</szFile>
</BitmapSmall>
<BitmapTiny>
<szFile>icon_scrapmetal_16.tga</szFile>
</BitmapTiny>
<BitmapCar>
<szFile>DSgoods.tga</szFile>
<uiX>32</uiX>
<uiY>0</uiY>
<uiWidth>32</uiWidth>
<uiHeight>16</uiHeight>
</BitmapCar>
<BitmapCarEmpty>
<szFile>DSgoodsEmpty.tga</szFile>
<uiX>32</uiX>
<uiY>0</uiY>
<uiWidth>32</uiWidth>
<uiHeight>16</uiHeight>
</BitmapCarEmpty>
<Color>78, 133, 138</Color>
<MinPrice>7000</MinPrice>
<MaxPrice>15000</MaxPrice>
<szIndustryLeaderTitle>Scrappy</szIndustryLeaderTitle>
<szIndustryPlayerTitle>Scooby</szIndustryPlayerTitle>
</Good>
Below is a shot from my playing your map, and there are the Scrap Metal cars and the Icons for them. (Please ignore the screen saver, i forgot to turn that screen off

)
And yes, mapping can get to be quite an undertaking. There are a SDSgoods.tga and a DSgoods.tga. A person really needs a set of lists of different types of files that are in the FPK files. I know I have one, alsong with an Icon folder and a CarIcon folder. But just going thru this post I found I had missed one set.
You have a nice map, and it requires either bridges and tunnels or curving trackage. The first time I ran track and caught the nose of one of those bears going accross the side of my screen, I jumped!
If you have any other questions, ask.
