It happens very often that I am having problems diagnosing a fault, particularly with electrical items.

My solution is to try and purchase the identical suspect item on EBay (used) and test by substitution then return to seller if no solution.

But finding the EXACT same part number is usually very difficult,

eg currently working on electric window and suspect the door control unit, original part nos 6G9T 14B533BJ, the closest I can find on eBay is 6G9T 14B533BL only the final digit is different. 

I normally assume the significance of the digits decreases from front to back and therefore the last digit being different does not concern me too much.

Am I right?

Hi.

6g9t - thus tells you the model year and lead programme.

14b533 - this identifies the part.

BL- this is the suffix. The first letter is the variant, and the second is changed every time the parts have a change that effects form, fit, or function.

So in theory : BJ is an earlier version of BL. But form/fit/function has been affected by the changes.

 

So for example AJ and BJ would be different parts so definitely not interchangeable.

BL replaced BK which replaced BJ... so could well work as a direct replacement.  But is not guranteed.

 

Hope this helps...