I’m not an accountant either, but I do write financial software that calculates stuff like this, although for companies and not individuals. There are differences (especially for tax purposes) but the basics are pretty much the same.
It kind of depends on how much detail you want.
In the case of your truck, the bottom line you’re looking for (the number that adds or subtracts from your net worth) is your current “equity” in the truck. If all you want is to calculate your net worth, it doesn’t matter much how you get that number. Basically it’s the current value of the truck minus what you owe on it.
If you want to put together an official looking Balance Sheet, then there are some conventions to follow.
Typically you list your Assets first, then Liabilities. If everything works out the difference between the two is your net worth. For a business, this number is usually listed near the bottom of Liabilities section as Equity and/or Retained and Current Earnings. This makes the Assets and Liabilities equal, and the balance of the Balance Sheet comes to zero, something the accounting types are big on. For a personal Balance Sheet I leave that out, and then the bottom line (all Assets minus all Liabilities) is the net worth.
Assets are your cash, balance in bank accounts, stocks, bonds, properties, debts owed to you, physical assets like cars and trucks, furniture, tools, clothes, jewelry, etc. The physical assets should be listed at current value or as the purchase price with depreciation (see below).
Liabilities are things you owe like mortgages, credit card balances, charge accounts, auto loans, money you owe other people, etc. Note that when you are figuring what you owe, only count the current month on your utilities such as your phone bill, electric bill, gas bill, rent, etc. You incur these expenses monthly, and they don’t have a “balance” in the way a mortgage or auto loan does.
In this form I would handle your truck with three entries:
First, a positive entry (a debit in accountant speak) in the Assets section for the purchase price of the truck.
Second, and usually listed right under the asset is a negative entry (a credit) for any depreciation on the truck since you bought it. The combination of those two (purchase price plus the negative number for depreciation) is (in a perfect world) the current value of the truck.
Third, a negative entry (another credit) in the Liabilities section listing the current loan balance. When combined with the asset and depreciation entries, the result should be your equity in the truck.
Month by month, the depreciation goes up a little and the loan balance goes down. Hopefully the loan goes down faster than the depreciation goes up so that your equity increases instead of decreases.
Clear as mud, huh? 
Ugly