No.  Your son has an aftermarket gas cap. To get all the locks working on the ignition key, he’ll need to find an OEM cap.  Compare the length of the structure on the inside of the cap between yours and his and you’ll clearly see the difference.

Jim

> On Apr 7, 2016, at 7:19 PM, John Graham <theklube@GMAIL.COM> wrote:
> 
> I have an '88 Westy and my ignition and door key also fits my gas cap lock
> - very convenient for me.
> 
> My son has just acquired an '89 Westy and his vehicle requires a separate
> key for the gas cap lock.  Can they be made/modified to unlock with the
> ignition key?  The separate key that the '89 requires for the gas cap
> appears to be a smaller version of the 'double sided ignition key'.
> 
> I'll patiently await the list's wisdom on this issue. . .
> 
> John Graham
> '88 Westy - Charlotte, NC

No problem is too small or too trivial if we can really do something about it.
-- Richard Feynman