On 1 May 2007 at 14:21, Jim Dwyer wrote:
> I removed then replaced the Oil Pressure Switch on the engine
> block... I plugged the 3 wires back in their correct positions.
Are you absolutely positively sure you hooked the wires back up the
same way???? If you didn't screw the sender back into the block the
same amount, the terminal would all be in different locations.
Here's a test. Get an ohmmeter, unplug the wires from the sender,
and check resistance between the various pairs of terminals. Do it
once with the engine off and once with the engine running. Here is
what you should find. With the engine off, one pair will show a
closed circuit (zero ohms), the other two pairs will show an open
circuit (infinite ohms). With the engine running and oil pressure
up, you'll get a different pair showing a closed circuit. Note which
terminal is common to those two closed-circuit readings. The ground
wire should connect to that one. Its behavior is to ground one of
the other two when oil pressure is up, ground the other when oil
pressure is down.
Now note which of the other two terminals was grounded when oil
pressue was down, i.e. the engine off. That one should connect to
the oil pressure light. You see, when you energize the ignition, it
powers the oil pressure bulb. If the pressure is down, that sender
switch completes that circuit to ground so the bulb turns on.
The other terminal goes to the anti-run-on valve. It works like
this. When you turn off the ignition, it de-energizes the ignition
and oil pressure bulb but it energizes the wire to the anti-run-on
valve. As long as the oil pressure is up from the engine still
spinning, that terminal is grounded and so completes the circuit for
the a-r-o valve. After a moment the engine stops and the oil
pressure falls, so the sender switches back to grounding the oil
pressure light but not the a-r-o valve. Since you've turned the
ignition off, the oil pressure bulb won't come on, and the a-r-o
valve won't stay engaged because the oil pressure won't throw the
sender switch that direction.
I didn't bother to work out all the ways you could have mis-wired
things, but it sound like you have found a combination that causes
the energized-when-igntion-is-off a-r-o wire to be connected to the
oil pressure switch, grounding through some other circuit.
--
Jim Muller
jimmuller@rcn.com
'80 Spitfire, '70 GT6+
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