I've got a 73 450sl that I just "tuned up" with new points, rotor, cap, plugs, plug wires, and air filter. I also took the opportunity to replace a lot of the vacuum lines. I also dumped a can of Sea Foam down the crankcase to clean it. All of that stuff went ok. The main reason for the tuneup was the engine was missing and idling very rough and very fast - about 1400 rpm even after warm up. I did find a broken sparkplug which caused the misfires and rough idle, but Icouldn't bring the idle down no matter what I did. It doesn't appear to have any visible air leaks. After all was said and done, I noticed the idiot engine light was now on. I haven't had this car long although it's been in the family since new. I would appreciate any help in determining how to locate the problem. What can turn the engine light on in a 73? Is it only an O2 sensor? I have a service manual, but Benz didn't put in any diagnostic or troubleshooting information into it. For that matter, I really can't find if there's any service codes, etc to read. Thanks in advance.

that model is way too old for a check engine light, self diagnostics or trouble codes , what color is the light, and where is it's position? it is definately not engine related.

Hi Ray. The light that comes on (now) is just to the right of the left turn signal indicator. According to the "book" it's a brake light...but the diagram in the light itself resembles an engine (sort of). When I was performing the "tune up", I didn't touch anything to do with the brakes. I wonder if this
was a coincidental problem that just popped up, or if when I was replacing the vacuum lines I messed up a brake vacuum line. Do you know if there is
such an animal like a vacuum assisted brake system. I seem to recall there is a vacuum line of a sort attached to the brake boost canister.

Thanks for the help.

Steve

can you send a picture of the light? some of those have a rest button on the master cylinder, it will be on the body, it looks like a little rubber nipple, push it in and see if the light goes off, also check the brake fluid level.this has power brakes, but you would know if it wasn't working, pedal would be very hard, and the car would be difficult to stop, the engine would run poorly if it were leaking vacuum

Chiming in here... I have a '72 and the light in question is a brake warning. Check the level of fluid in the brake reservoir like Ray suggested. There is a float inside the cap that triggers a light when the fluid level drops, as in when pads wear and the caliper pistons move out to compensate. If the fluid adjustment does not fix it, then look at your E-brake and make sure it is releasing completly. If so, the switch may need to be adjusted slightly. If the fluid level adjustment fixes it, then consider looking at your brakes, the pads may be wearing down. If you replace them, then you'll have to remove some of the fluid you added or it will over-top the reservoir. Remember, brake fluid will remove paint, be careful.

If none of the above fixes the problem, look for a leak, and do it now.

230/8

Thanks. I check the fluid and it's ok. I'll crawl in and have a look a the
emergency brake release. It seems to release ok. I'll also check the
switch on the brake pedal to make sure it's got the play it should have.

Ray, I sent you a pic but I think it's probably the brake indicator. It's just
kind of strange that it started doing it immediately after the tune up. But
you know how it is with these old beauties......

Thanks again.

HH

I found the problem. The front reservoir float had separated from the
contact rod thus closing the circuit and causing the light to come on.
I can disconnect the front reservoir plug and the light stays out. THe
back plug is still connected and works to monitor the fluid level. This
is just a short term solution until I can figure out if I can repair the float
indicator or whether I'll have to buy a new reservoir. Does anyone know
if there's a kit to fix this? BTW, Thanks to all for the assist.

i am going to the junk yard today, send me a picture of the reservoir, if it is the type i am thinking of the float is replaceable, let me know i will get you one