Does this sound like a doorlock problem in car??
 

I can't figure out to lock my car doors--BESIDES being inside the car.
When I open driverside door and push down on the door lock button--it doesn't want to go down and lock, unless I shut the door and then it will go down and I can hear the locks actuate. The passenger side seems to work fine, the doors will lock of course if I manually lock it outside. I wish I had that infrared gadgets, the scanners are on the doors...I'm not sure if I need to replace a part in the door or just have a keyless entry installed....this is a 91 sl 500

It's operating as designed. You can't push down on the lock button on any MB while the door is open. This prevents you from locking yourself out of the car by leaving the keys inside.

To lock the car you can use the key in any of the locks (including the trunk). Or use the remote control thingy, which you apparently do not have.

All this is spelled out in your owners manual, if you have one.

no, I didn't get an owners manual, just bought this car 2 weeks ago. How do I get an owners manual ? and is this the same as a shop manual that mechanics use at mercedes ? thankyou for the help, I might just look for a keyless entry/security system

Your car already has the keyless entry and security system. By the time you by a new system and install it, you will spend more than it costs for a new "infrared thingy". Go to your local dealer with your key and VIN and get a new one.

cool, so my car would definately have the infrared as a factory option? I'm not sure where a local mercedes shop is around here, I'll have to search it, but what kind of security does it have? I might just go to a mercedes dealer tomorrow...

Called Mercedes in Gainseville, they quoted me $217 for 1 infrared remote----does anyone know if that includes a cut key that whips out like a knife and whether it can be used for ignition? I test drove another persons 90 and he did have this same key.

Yes, that's the key. You pay for MB to program the infrared to match your cart. Any locksmith worth his salt can cut the key to match the one you are currently using. I had several spare, plain, keys cut from my infrared master just in case. My local locksmith did it.

got one ordered, I'll have it next tuesday..thanks Mike for your help

Call your dealer and get an owner's manual or get one off ebay if you can't get back to the seller and get it from her with other records on the car.
Try also for the accessories booklet, maintenance stamp booklet, factory warranty booklet, radio booklet, everything that the car came with when new.
Try and get the dealer service or parts guy to print out for you a copy of the
Vehicle Master Inquiry (also called the MB net), it will list warranty repoars performed on the car at the MB dealer's, also other information, like date of build, where first sold, accessories. But it it's in code, have them translate it for you

Call 1-800FORMERCEDES and ask for a (free) copy of the factory window sticker for the car. Call that number too, if you ever need a battery jump, flat tire change or run out of gas. Mercedes will send a truck out for free and take care of you, they will even install a new MB battery on the spot for you with no labor charge, a much better deal than having it done at the dealer who might charge you labor and require an appointment. You don't need to be the first owner of the car for any of this

The owners manual is just a booklet, but it's worth owning for any car to familiarize yourself with its workings, fluid capacities, fuses needed, operation of accessories and so on

The HUGE Chilton and Haynes manuals are for the mechanics, as is a suscription to Alldata.