OVP pin15 ?

[bclem]

Hi all, i just purchased an 89 300E with an electrical gremlin and I'm hopeing somebody here might be able to shed some light on it. i suspect that the problem is in the electrical portion of the ignition switch but would like a confirmation before jumping in there.
A little history:
The car has 115K miles on it and appears well taken care of. The previous owner related the following: She was driving home from work about a year ago and the car started running rough and died at a stop light. She got it to restart and drove it home (aprox. 5 mi). Thereafter it would not start. An indy shop (not familiar with MBs) replaced the idle air valve with no cure of starting problem, she had the car towed home where it has sat until I bought it.
I put fresh plugs and a fuel filter in it and it started up and ran very well to my house (aprox 15mi) EXCEPT that after the initial startup and before leaving her driveway it died after about 5 min of running but restarted immediately.
When I got it to my house I started playing with it starting, killing, restarting etc. to see if I could recreate the no start problem. Sometimes it would start fine and other times it would crank but not start. I then noticed that the times it started that all the dash warning lights would light up across the board and all go out when it started. During the no start condition the only lights that lit were the SRS and CE and sometimes only the SRS. Also during the no start conditions I can hear the fuel pumps priming when the key was turned on and sometimes the car would catch for a second (I suspect from the residual pressure in the lines) but not run.
I would suspect the normal gremlins of OVP, FPR, ECU if it were not for the actions of the warning lights.
While taking a voltage reading at the OVP plug I only read about 1 volt at pin 15. I know that pin 15 is supposed to recieve a full 12v when the ignition is switched on but what is the exact path from the switch ? Does it connect directly with the switch or does it come thru another relay, bus bar, multi connector or what ?
I also read low voltages at fuses B, 5, 6 & 7. Now here's something wierd, if I momentarily jumper 12v to any of the aforementioned fuse holders they all begin to read 12v (with jumper removed) until the ignition switch is turned off but on turning the switch back on they revert to low voltage until momentarily jumpered again.
What the fork, Batman ????????

[MattBelliveau]

Have you checked into the fuel pump relay? Try jumping that one.

[david s poole]

yes you need new electrical part of ignition switch.

[saumil]

It looks like from the run point on the ignition switch, the wire goes to the fuse box where it connects to fues 7, B, 5 and 6. The same connection then extends to the OVP relay and fuel pump relay. So if you get a low voltage on fuses 7, B, 5 and 6 as well as OVP relay coil terminal (15), socket terminal 3, (and likely on fuel relay terminal 15, socket terminal 9) then the ignition switch is bad or there is a short somewhere in the fuel pump or ovp relay. Make sure you do the test with fuel relay and ovp relay removed from the socket as well. If the switch really goes bad because of the load or is it bad regardless of the load, is the question this will answer. Let us know what you find.

[bclem]

OK, I took the ignition switch apart and sho nuff, the contacts for pin 15 on the switch were dirty and misaligned. I cleaned and aligned all the contacts and reassembled the switch. Works like brang dang new. Now I need to track down why the cruise don't work.