Unknown dash light.
 

On my 90 560sel, the red light with no symbol stays on. The light is located second from right,next to the check engine light. Does anyone know what this light is for,and what possibly is the problem?

when you do a self test on that side with key on engine off is there any with an icon that are not illuminated? if so the bulb is likely in the wrong port

This light suddenly started to stay on. It usually comes on at startup and goes off ater 2 or 3 seconds.

on that side it could be the check engine light, srs or abs, but in the wrong spot. maybe seatbelt as well?

bkbs22, the Owner's Manual describes/identifies all the dash warning lights.

You could be low on oil. Have you checked your dip stick?

There are no "unmarked" lights on your dashboard.

If you have one, someone has inserted bulb in wrong spot.

You can test this by looking for no light in a postion with an icon when first turning on ignition.

oil light is on the other side of the cluster, not likely his issue, his light is on the right cluster area

I have discovered that the light is the accessory light.But why suddenly it's staying on is now the problem.

Carson 357 is right.I pulled the cluster,and there is no bulb going to the SRS socket. So its my SRS light thats on.

Just had that happen on my SL. Diagnostic code indicated a bad control module. Replaced it and all is well. I suggest you read the codes before throwing parts at it if in fact you care to fix it at all.

How can I have the codes read without taking the car to the dealer.Is there an inexpensive tool or equipment that I can buy?

Did you buy the car used? I found out the hard way that some dealers will pull the trouble lights out of thier sockets and bury them in the dash before selling em. Mine had two this way. Couldn't figure out why it was soo bright behind the dash.

JimF has an excellent site on troubleshooting various systems as well as the code reader. Her is the link to his reader page http://pages.prodigy.net/jforgione/MB_X11.html

For future purchases, I will be sure that ALL trouble lights flash when turning the key, otherwise I will be looking elsewhere.

I had the code read. Code #3 which is driver air bag.Does this mean that the air bag should be replaced or is there a part connected to it that should be replaced.

I had a Code 2 on mine, i.e. control module. Maybe you just need to check the connection to the airbag in the steering wheel? Steering wheel has to come off for that. If you do that, then you should inspect and at least clean the contact rings. Just a guess on my part - others will know far more about it I'm sure.