Cali glow plug module
 

I have an 04 California emissions
I need to find out how to test the module to see if it's good
Checked glow plugs and wiring to module from glow plugs
There is 12volts going to the module from the battery
The wire from the battery goes to a lug on the module and there is also a smaller wire also attached to the same lug, what is the smaller wire for?
Any help would be appreciated, I want to make sure it's the module before I fork out $160 plus shipping
Thanks

surely there must be someone who can help me, i have to try and get this fixed so that i can get it back to work, i have very little money so i cant afford to take it somewhere to have it checked, and i use it as a work truck