I sold a mobile home to a married couple using an installment loan
contract. They have the title showing me as the lien holder. There is
no real property involved as the mobile is on a rented lot. I'm not
getting paid. What is the procedure to take back the mobile? This is
in Arizona.

lucyfur,
The procedure to follow is similar to repossession of a car.

When 90 days have elapsed (since the last payment on the lien has been
received) a letter needs to be sent to the owners (i.e. married
couple) that they are in default of the agreed loan contract and if
the mobile home is not returned within 30 days they may be subject to
criminal prosecution. The letter should include reference to the
original contract (clauses involving what happens in the event of
default) where the home should be returned to and the letter must be
sent certified mail return receipt (so you have proof that they got
it).

After the 30 days have elapsed you are entitled to collect the mobile
home provided it can be done without breaching the peace. As this is
unlikely and raises issues regarding the current owners personal
possessions (theft?) and trespass (to collect the mobile home you
would be entering another persons private property?) you would be wise
to consult a lawyer and law officer prior to issuing the default
letter.

But the first thing to do is to talk to the current owners, not in a
harassing way, more a wondering what the heck is happening way. Try to
come to an agreement before it gets nasty.

But if it is nasty protect yourself first (Law officer/Lawyer) then go after them.

References:
http://www.lawdog.com/states/az/repo.htm
Various state statutes: 13-1813
http://www.azleg.state.az.us/FormatDocument.asp?inDoc=/ars/13/01813.htm&Title=13&DocType=ARS
28-2060
http://www.azleg.state.az.us/FormatDocument.asp?inDoc=/ars/28/02060.htm&Title=28&DocType=ARS

Kind regards,
gfmaster

Title companies, at least here in NV, will do it for you.