300E electrical mystery

[John Hockin]

My 300e has exhibited strange elecrtical, behaviour for the last 4 years. After 2-6 hours on the highway in the summer the SRS light starts to flash irregularily. Eventually it has actually come on and stayed on. during this period if i come off a ramp and stop the electrics will often fail completey and the car dies at about 40KPH. The car has always restarted right away.
This happens only in the summer when the engine room is hot. BUT the electrics have also often failed when i slow down at other times in the year in city traffic, when the SRS light is not on. Some times this can happen three times a day and then not reoccur for months.
I believe the car was in an accident ( pass side) before i had it and think maybe it is related to this.
My mechanic ( excellent) has never been able to find the problem nor has anyone else i have ever discussed this with.
Any idaes out there??????

[mpolli]

I have been sitting here waiting for an electrical problem to come along... You don't say what year it is, but I don't have a specific cure for you anyway. However, my years as an electrionic tech taught me that connectors and solder joints are the root of all evil. And when you have an imperfect crimp, a connection that has gone bad for some reason (corrosion, heat etc), or a bad solder joint, these things can be very heat sensitive. And sometimes they take years to appear. Considering the miles of wires in a car (OK maybe not miles) and the hundreds of connectors/connections (several hundreds), there are lots of opportunities for trouble. It could take a trained electronic tech with a schematic quite a while to find the trouble. Hopefully, with a schematic, you can look at the symptoms and see what might cause these problems, but it might be a long shopping list. The key to fixing something is recreating the fault and this can be hard to do. The wiggle test sometimes helps as does tapping on suspected bad connections. Hopefully some one out there has had the same trouble and can point you in a specific direction.

Mike

[Arthur Dalton]

Check the charging circuit .. possible low voltage condition,... suspects are Voltage regulator/brushes and possibe OVP..
Also, check grounding cables for poor connections

[bender]

do a search on OVP Relay, you will see a myraid of electrical ghost descriptions.

[airedale]

This story sounded good to me so I purchased it and installed as preventive maintenance.
John

Run Insurance (Voltage Regulator)
Item # COMEKU-RIN

COMEKU - FITS THE FOLLOWING: all 107, 116, 123, 124, 126 and 201 chassis.
The only time in my life when I have been stranded on the freeway with a dead car was when the voltage regulator went out in my 1986 230E. The brushes wore down to a point where they were making enough contact to not have the dash warning light come on, but not good enough to keep the battery charged. When the voltage got low enough in the battery the ignition system shut down and the car quit dead going 70 mph. First indication of a problem is your wipers start to slow down or the lights start to dim. And they won't start the next time you try. As these old Mercedes approach 20+ years the brushes are wearing out and the alternators are failing. Many owners are having their expensive alternators replaced without knowing that it might just be the inexpensive voltage regulator mounted on the back on the alternator. I am now taking a preventative approach with my customers and just replacing all the old voltage regulators. This small regulator is easy to install by jacking up your Benz and going underneath to the back of the alternator. I especially like the quality German KAE regulator because it has extra long brushes. If you have not replaced this unit in the last 5 years I would highly recommend you do....... One of the best run insurance measures you can take!

Includes picture installation instructions and troubleshooting tips.

http://www.**************.com/store/item.php?item=Run%20Insurance%20(Voltage%20Regulator)

[schumi]

If you want to replace the OVP, I have one that is like new (used a couple hours) that you can have for $35 plus shipping. I bought it to troubleshoot an idle problem and it turned out to be something else so I have a spare.

[mpolli]

2 questions:

Why is the Voltage Regulator called OVP? Is that German for "Voltage Regulator"?

Does the 202 have that kind? Looks just like the one in my old Fiat 131. Same problem with that one also.

Thanks,

Mike

[schumi]

the voltage regulator is not the same thing as the OVP (over voltage protection). the OVP is a relay that acts like a fuse to prevent damage to electronic components in case there is too much voltage. the voltage regulator is supposed to limit the voltage output by the alternator; if the volt reg goes out then the voltage will climb (and the OVP may have to step in to save it).

[d2bernhard]

not exact, but similar.

O2 Sensor Test Lamp