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Old 02-02-2011, 11:05 AM
Alex300DT's Avatar
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Question Wiring mystery. 1987 300D

Hey guys, ive been searching the forums with no avail.

I'm trying to figure out what the previous owner has done to the OVP wiring circuit. Everything on the car works fine without the OVP relay being plugged in and when i have a fresh fuse and plug the whole relay into the car, everything stays on just like the key is still in on position. im wondering if anyone has come across anything like this before? and where would i look for bypassed ovp relay that affects the ignition?

thanks for any help
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Old 02-02-2011, 11:18 AM
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Please confirm: with the OVP relay in place, everything stays on? Engine continues to run, etc.?

Sounds like the OP had OVP problems and wired around the OVP to power its circuits directly from the ignition switch. Are there any signs of jumpers being added in the fuse box? Wires attached to fuse terminals?

I would then pull the OVP relay's bracket and see if there are any obvious signs of changes or additions to the wiring. Given the location of the OVP relay behind the battery, this is not a trivial task but it needs to be done.

The other "first place" I'd look is the ignition switch itself. With the driver's under-dash panel off you can look up under the dash to see if it's wiring has been obviously modified. [Most people doing things like this don't do a very neat job; you can tell just by looking that some of the wiring isn't factory.]

"Buster" in the '95

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Old 02-02-2011, 07:37 PM
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Yes, everything stays on just like i had never taken the key out, i did not get a chance to look at the car yet, (too cold outside) but i will take a look at the ignition switch and report what i see asap.
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Old 02-02-2011, 08:32 PM
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I'm parting out an 87D soon, you're welcome to the harness.
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Old 02-02-2011, 08:38 PM
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So the car starts, runs, tachometer/ABS/Cruise/A/C work normally, the car shuts off normally without the OVP relay?

Then with it plugged in, everything still works normally, but the car won't shut off, and tachometer remains working with no warning lights?

Just trying to clarify the original problem.

If this is the case, it sounds to me like the ignition switch has failed internally, is no longer linked to the lock cylinder. Shutting off the engine is achieved by a mechanical valve on the ignition switch assembly that opens and allows vacuum to the shutoff valve when you turn off the key.

You might want John's ignition switch assembly.

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Old 02-02-2011, 10:15 PM
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He might want to simply check if his vacuum system's ok, and set the OVP issue aside for now since it has nothing to do with the engine continuing to run.
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Old 02-04-2011, 03:25 PM
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Location: San Antonio
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Hey everyone. Thanks for the replies. After checking the vac shutoff, tearing the dash apart and not finding anything weird there I went back to the engine bay and found a wire going from the switchover valve towards the governor. I have no idea what the previous owner was trying to accomplish with that but it seems to be working perfect now.

Thanks again.
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