Okay, I know these questions get asked a million times, and I've searched high and low, but I can't seem to find what I need. What I need is someone who knows the answers to enlighten me on this subject.

Here's what I've been dealing with: This is an '84 Z28 with the 305 HO engine. This is my wife's car that I've been restoring for her. Before I came on the scene, the engine was rebuilt, and whoever did it apparently has a hole in his head. I've discovered wiring issues galore. The CTS was where the fan switch goes, the fan switch was where the temp indicator switch goes, and the temp indicator was where the CTS goes. The wiring for all three was cut, spliced, added to, pulled over, etc to get the wiring to the sensors. So far, I've relocated these three back to their proper locations and routed the wiring the way it's supposed to go. Apparently, the mechanic who worked on the engine didn't know locations and didn't bother to record anything before yanking the engine.

Now, I've found an oil pressure sender located above the oil filter. It's a two blade sender, and from what I've seen on the wiring diagram, it's supposed to drive the gauge. It's disconnected, and there are no wires running down to this device.

Also, there is an oil pressure switch (?) located next to the distributor, driver's side, mounted in the block. It's the single blade, bell shaped sender. From what I've seen on the wiring diagram, it's supposed to turn on/off the oil pressure dummy light. There is a single tan wire running to this device, and instead of being connected to the dummy light, it's connected to the gauge.

This is the wiring diagram that I'm referring to: http://austinthirdgen.org/mkportal/m..._continued.gif

Questions:

1) Am I correct in that the single blade switch next to the dizzy is supposed to be connected to the dummy light and that the two-blade sender next to the oil filter is supposed to to be connected to the gauge?

2) Any idea what group of wiring harnesses behind the dizzy that the wiring for the two blade sender (next to the oil filter) comes out of, or does this wiring come from somewhere else?

3) Is this wiring diagram even correct? The single-blade sender/switch (whatever it is) next to the dizzy does drive the gauge, so why would a two-blade sender (next to the oil filter) be needed to drive the gauge?

If I can't find the wiring for the two-blade sender next to the oil filter, then I'm just going to remove that sender and plug the hole because that sender is beginning to leak. If it's not ever going to get used, then why bother with it?

 

There were several different types of oil pressure sending units (gauge) and oil pressure switches (dummy) over the years.

The "bell" shaped unit is a sending unit for the gauge and used on most pre 88 Thirdgens. It's normally mounted on top of a brass fitting that's screwed on the top/back of the blocks' china-wall. There are V6 (40-80) and V8 (30-60) sending units of this style. ( Uses a tan wire )

Many V6 cars and later V8's used yet another type of oil pressure sending unit that got mounted above the oil filter. This spot is where I've found most "switches" too.

Normally I'd say:
Disconnect the Tan wire and check your gauge. If the 'bell' sending unit is controlling your gauge than simply plug off the other hole and your good-to-go !

However; If your car is a factory HO than you might have a Electric "in-tank" Fuel pump and the second O/P sensor might be the F/P cut-off switch.


Does your car - or did it - have a factory installed in-tank Fuel pump ?

 

Well, for one thing, the bell shaped sending unit next to the dizzy is the only unit that's connected, and the gauge works. Soooo ... I'd have to conclude that this unit does, in fact, drive the gauge. It's like you described. It's mounted on a brass fitting and has a tan wire connected to it.

It doesn't have an in-tank fuel pump. It's a mechanical pump with the two steel tubing lines coming from the tank, one for the supply, and one for the bleed-off. (I assume that's what the second line is called.) I don't know how many lines come from the tank with an electric fuel pump. I'm assuming only one. If that's the case, then I don't believe this car ever had an electric fuel pump.

The wiring diagram shows that there is an oil pressure dummy light, and it shows a second sender/switch connected to it. I can't figure why a two-blade sender would be needed for that. That's why I asked if the diagram was correct. I'll be checking a few bulbs in the dash in the coming days. One of the turn signal bulbs isn't making a good contact in the connector, so I'll have that gauges pulled and checking/cleaning connectors/sockets. I'll look to see at that time if there is, in fact, an oil pressure dummy light.

I will also look in the corrugated wiring conduits coming out of the firewall to see if I can find a pair of cut wires that is supposed to be connected to the sender next to the oil filter.

I will probably end up pulling that sender and plugging the hole. The reason it's there may forever remain a mystery. lol.