Choose from drop down list whose values are obtained from another drop down list

Attached is the file 06-07 1500 Express.xlsx (You will need to rename to .xltm)

Worksheets are:

06-07 1500 Express (where I want the magic to work)
EngineCodes (table where only columns A and B are relevant for A20 & B20 noted below)...the rest was my trial and error...mostly error.
Lists (lists of all the drop down lists)
Troubleshooter Database (what I fill out each time a new test and fix was performed on each vehicle. I currently have linked in the code and description from worksheet Enginecodes).
Code Search (a tool for the Mechanic to quickly view tests and fixes with the highest success or failure rate)

So on Worksheet 06-07 1500 Express I have the following working correctly:

A20 is a validation list based off information in table "Codes" (table header "Code") on sheet Enginecodes.
B20 is a VLOOKUP function based on the same table used for A20 (table header "Desc")
C20 is a validation list using the =INDIRECT(A20) function. The named range is located on sheet "Lists". I have several lists, and the overall range for all lists is L1:EG15

Here is what I need:

G20 I need a drop down list based on the selection in C20.

I tried another indirect using a different list but I get an error. I am not entirely sure how to best format my data source (lists or a table) in order to best retrieve this information.

What it all should look and function like is:

A20 = Engine Code (Mechanic chooses a code from the list)
B20 = Description (Automatically filled out)
C20 = Tests (Mechanic chooses a test from the list, or if none exists, he will type in a new test)
G20 = Fixes based on selected tests (if previous test was selected in C20, then another list will be available to choose a fix from).
J20 = Fail (Mechanic will choose if the test and fix selected or entered failed or fixed the issue).

If a mechanic has a code issue, I enter in the data on the Troubleshooter Database worksheet based on the information above.

On the Code Search tab is a pivot table where the Mechanic will go to first to find the best option to test and fix based on previous entries in the table on the Troubleshooter Database worksheet.


Let me know if you require any further clarification.

Change to .xltm...it's a macro enabled template file.