I bought a trailer from someone and he had the supra lock box on it and I asked him what was that and he told me and also told me he lost the combination # and I found it written on the inside of the door and he was surprised and tried it but it wouldn't open. I bought it anyway and figure I would figure it out. Now I have tried everything and it wont budge!

NO COUNTRY TOLD. NO YEAR TOLD IT. WOW, HARD.
THIS IS THE WWW, HERE, AND TRAILERS ARE NOT THE SAME
(USA IS TRAILER.) SO WAS SOLD HERE. 21 YEARS AGO.

GOOGLE SHOWS THIS.
2001 Mallard 30' Trailer with 1 slide out for sale in Golden Isles, Florida OR
Fleetwood Mallard 300bhs BEST IS GO TO ANY RV CENTER AND ASK ,WITH VIN
OR GOOGLE ENDLESSLY .
MAYBE MAKER HAS SUPPORT, IDK. TRY?

pick the lock, Manufactures reset or hire a lock smith.

https://www.hunker.com/12399239/how-to-open-a-lock-box-with-a-lost-combination

see if the current combination is 0-0-0 as sent from the factory
once you find the combo use a pin or other to depress a button where you can choose another combo
or try here
http://www.ask.com/question/supra-lock-boxes

Perhaps the Chrysler Corporation will not warranty or authorize the 7 pin system for two reasons. 1) The vehicle may not be structurally compatable with a trailer heavy enough to need electric brakes. (This is extremely likely). That means , if you hook up such a vehicle, and something goes wrong, Chrysler does not want to get sued becasue your car wrecked and it was the trailers fault. 2) The 7 pin system includes a "hot" wire from the battery or fuse box or wherever, and the Chrysler makes no such electrical harness on their cars. They also know, if you add such a harness, and it shorts out, they are responsible for any ensuing fires.
That being said, most any company who sells trailers might add the wriing harness and fix you up, but a good way to start would be to go by a "U-Haul" outlet and ask them about it. If they find in their literature they cannot add the 7 pin harness, you may have to find someone who can "cobble" it for you.
Be blessed.

Well there are may ways,,, I cant really post them here as this is public and a lot of BAD people use the net too.

I once forgot my combination but I used this basically it will generate every possible combination for you, a 5 digit sequence will take about 20 minutes to go through..

Also I remember once a friend left for vacation. While he was out a clever Thief used battery acid to melt away the plastic coating and then used a chisel and hammer or something abound that thereof to break the rest open.

and as another friend told me, When all else fails a Huge Hammer works.

Please remember these locks are Advanced and you should call a locksmith as it will be wrong of us to tell you how to bypass.

Well, you MIGHT be stuck and out of luck, however there are some tricks you can try. Check out the blog on http://suprakey.org/ - they have several solutions for those that need to reset the combination of a Supra Key lockbox!

Good Luck!

You can order a manual at the following link; http://steprightupmanuals.com/refrigerator-service-manuals/carrier-truck-and-trailer-refrigeration-service-manuals
Just select the Supra 644 through 844 series and I believe it is $6.99 to order from this site.

I have just moved into a house that has a supra combination code key safe mounted on a wall outside the back door , it was put there by the first owner who died ,the second owner never used it and don't know the code,I just thought it would be handy to use as we are going away in June to France and its away of leaving a key in case the alarm goes off while away so a neighbour could deactivate it or the police so they don't have to brake down the door or if I get locked out I could have that key for emergencies so is there a way I could find the code for the safe please?

you can try calling the maker of the pc and give them the ss number for a restart disk or replacement disk good luck.

You can get parts for the Supra SW5L30D from EdgeStar (can't figure out if EdgeStar bought Supra, or if Supra just changed their name or what). 866-319-5473. I've been able to get the parts I've needed, though they're not the most efficient operation. One time I had to wait for someone to get back from vacation before the part could ship...