yes the ground behind the gauges is considered the main ground by MB for some reason.

anyway test the continuity of the sockets of the OVP, pin hole 3 should show continuity to fuse 6 in the fuse panel, pin hole 1 should show continuity to the main power block ahead of the battery. The ground is pin hole 5 and is tied to the ground besides the main battery negative cable lug.

These are the main power distribution points of the relay.

The relay itself has a diagram that shows the relay orientation in basic Bosch wiring code.

also check continuity from point 15 of the ignition switch to fuse 6.

I checked pins 1 3 and 5. All look good.
How about pin 6 and 9.

Also where is the pin 15 for the ignitian.

Could it be that relays are bad. I removed the egr klima and elr relays and started checking pins. I did find one pin that was 14v and another that was 0 on each relay socket.

The pin 15 of the ignition is on the ignition switch itself, when you switch on the ignition do you get voltage at fuse 6? This circuit activates the OVP relay to switch on and supply voltage to the modules it protects.

Does this engine have the resonant intake system the same as the 96 model E300D?

of course it does.

I do see a voltage when the ignition is switched on.

If the OVP relay is new, can you get your hands on a known good ring gear sensor? Check the wires to the sensor on the bell housing flange below the oil filter.

Sixto
87 300D^2

If you have voltage at fuse 6 and continuity to the relay and the relay has its ground, the relay is relaying voltage from the main 3 pole connector then the relay must be working, you can verify this by removing the ELR relay and checking for voltage there, it also spiders off the EGR and other bits n pieces.

check the rpm sensor connector too.

I tried to find the drawings from looking at the website, but there were not drawings available. It said that I could click on the links, but these did not work. Do you guys have the drawings that you could send me. I would like to take a look at them if possible

Does anyone know where the 12 pole engine harness is located?

I finally found some time to look at this again. I found that the rpm sensor cables was pinched and I repaired it. Now the tach is working again and it feels like the car has a little bit more power. I tried a 0 to 60 and was able to get 19s. I know it should be more around the 12s.

The AC compressor still never comes on and I do not see the egr flap moving at all. Usually when the car is at idle you can see the flap move back and forth slightly.

I also noticed that the car now idles much better. The idle control is working.

Anyone have an idea what I should look at for the egr and also the AC?

the 12 pole connector for the engine harness is right behind the battery - its placed in the black plastic holder that holds the relay units, If you remove the splash cover and remove the little tray that slides up in front of it - you can see the 12 pole connector of the main wiring harness. The safest way to disconnect is to remove the battery first.

The EGR and flap are controlled by two vacuum transducers controlled by solenoids via the EGR controller with inputs from engine rpm, temperature and accelerator position (the position is sensed off the pump) There are two transducers below the air filter box whose wiring comes from the same relay junction but is routed from the side of the car, In my car there were 3 wires that had corroded with battery acid boil over right besides the battery. It was causing some strange issues including choking for air, but in that case I was seeing black smoke. After I fixed it - I disabled the EGR and now the engine revs like a high perf gas engine.

The A/C also has a relay its called klima relay and is right next to the OVP. but to isolate it out - first check the compressor magnet coil that it actually works - then check wiring continuity - Its wires are in the main wiring harness.

the acc fan also never comes on. I took the car on a long trip yesterday and the temp was pretty high. It was around a 100C. I turned on the heat and put the windows down. That kept it around 90C.