Hi

I'm new to this board but I'm grey hair to troubleshooting.

I was coming to this board because wifey Benz suffer from a gremlins.

You know the stalling problem when you decelerate at a stop. Wifey benz does it when the engine temp reach 85C and you decelerate. She have to fully depress the trottle pedal and crank it for about 30 secs and it will re-start at that point the idle will play from 1000 to 500rpm after a minute or two it will set up and the engine temp will rise to about 90C. She could drive the car for 100 miles after without any stalling unless she stop the car and let it cool down.

So now wifey is like Cendrillon she have to be back home before 85C. :-)))

When I do a search on this forum there is a lot a post pointing tower the Over Voltage Protection relay(OVP).

Being familiar with relay, I know they can be tricky but we can test them.

First this relay is not an over voltage but an over current relay it is built for 10 amp if you ask more than 10 the fuse on the top will blow this will protect your component from over current.

Why are we using relay?
To protect the ignition switch from overheating. The ignition swtich just activate an electromechanic plunger(few amp) to close the circuit and let flow the power from the battery to the component.

How can we test it?
First test the wiring harness:
Ignition switch OFF
Unplug the connector, use a test lamp or a multimeter check all the pin from the connector for power. You should have one pin with battery voltage this is the pin 30(always). If you can't find one, this is a wiring harness problem check for broken wire or bad terminal.
Check on the relay to find the pin 31 this is your ground find the connector terminal who plug to that pin and check it for ground this can be done with a test lamp or ohmeter.
Ignition switch on
Again check the connector pin for battery voltage you should have two pin with battery voltage the pin 30 from our previous test and the pin15. If you can't find two pin with battery voltage again check the wiring harness.

What we achieve with does test is:
Make sure we have battery power to the relay
Make sure the ground is good
Make sure we have power from the switch to activate the electromagnetic plunger in the relay.

Testing the relay:
We might use jump connector or just plug the relay into the connector so we can touch the pin with our test lamp or our multimeter.
Ignition switch ON
Now you should test for battery voltage on pin30, pin15, and all the pin87 should have battery voltage. if not throw the relay in the glove box and buy a new one.

This is a standard test, if you think your relay do not work under certain temperature just use an hair dryer to overheat it or put in the freezer to cool it down and re-do the test. You may do a load test using a 55 watts sealed beam on any pin87, do this one on the bench with jump wire.

Now that you read all this here a hint I have 3 different diagram of this realy for different Benz model all diagram show that if the realy do not work the abs light will come on.

Well I still searching for the gremlins in my wife car my relay is good.
If you're a tech and know where I should look next let me know.
Hope this post will help some of you.

Max
John Deere Combines Specialist