Wiring of Oil Pressure Safety Switch

[forcenine]

Don,
I've attached a picture of what I believe to be my oil pressure safety switch which must have been installed when my new fuel pump was installed. As you have written, there is a wire from the positive side of the coil to the blue fuse and into the assumed switch. My problem is that the two other wires at my fingertips were left unconnected. I guess the thicker black is a ground and perhaps the other is neutral but what do I do with them? DO I connect both to the engine block?
Thanks a lot.
Lisa ("forcenine")
Cat 27 "Knot His"

[Don Moyer]

Lisa,

Your photo is indeed of the oil safety switch, and the lower contact should be connected to the pump.

In the original Universal configuration, the lower terminal was also connected to the "R" terminal of the starter solenoid to provide power to the pump while the starter was being energized during starting. This would have been the second wire you were asking about.

We have discontinued using the wire from the "R" terminal due to the fact that the starter solenoid would occasionally create a spike of current back through the fuel pump circuit from "inductive feedback" which can blow the fuse between the switch and the coil. Universal never had this problem because they didn't install a fuse between the switch and the coil.

Don

[forcenine]

Should I Remove Bottom 2 Wires Then?

From your response, Don, the top wire with the blue fuse should be changed to the bottom input where the 2 unconnected wires reside. Should I take off the lower 2 wires altogether and not connect them as grounding wires?
Lisa

[Don Moyer]

Lisa,

Leave the wire from the coil attached to the top terminal where it is currently connected. Connect the pump lead directly to the lower terminal of the switch.

I can't tell much about the two wires that used to reside on the lower terminal from your photo (or even if they're still residing there), but one of those two wires would have been the lead from the pump. If that's still the case, you can leave that wire connected to the lower terminal of the switch and cut the other wire off which used to go to the "R" terminal of the starter solenoid.

There are no requirements for a ground. The pump grounds through its mount. You can completely ignore the original two wires that used to go to the lower terminal of the switch.

Don

[forcenine]

Bad switch preventing start?

Hi Don,
Rewired the oil pressure safety switch as per your advice. The engine cranked but did not turn over. A check of the fuel line at the fuel pump revealed no fuel getting pumped into the fuel pump. The fuel pump is brand new. Then I discovered the oil pressure safety switch seems corroded so I have ordered one from you. Could that be the sole source of the failure to start? It's already been determined that the compression is OK, and the carb is rebuilt.
Lisa (forcenine)

[Don Moyer]

Lisa,

Corroded oil safety switch terminals could indeed prevent power from getting to the fuel pump and prevent the engine from starting.

Don

[ArtJ]

rewiring replaced fuel safety switch

Don
I just replaced my fuel safety switch today. I wired it originally per the
instructions given 10 years ago.

I just replaced things, copying wire for wire.

Therefore, I have the case of the switch and the pump case both wired to ground.

The Pump hot lead goes to one terminal of the safety switch

I have connected the starter R wire and the wire, via fuse from ignition, to the
other terminal.

Should I now remove this R Terminal wire ???

Thsnks Art

[ArtJ]

From perusing the above discussion, it appears that the R wire was
supposed to be on the same side of the switch as the Pump. Do I
have it on the wrong (ignition side ) of the safety switch?

Probably a moot issue in any case, since you suggest removing it, but
wonder if i have it miswired currently.

[thatch]

That depends...

ArtJ,
You are correct in assuming that the wire from the solenoid terminal marked R, belongs on the fuel pump side of the pressure safety switch. The R terminal is only hot when the starter is energized and gives the fuel pump power while oil pressure is building in the engine. Current thinking on using or not using this extra circuit seems to depend on weather or not there is a fuse in your fuel pump circuit. If you have the fuse, remove the wire if you don't have the fuse, leave the wire in. My A4 dosen't have the fuse so I still have the R circuit in place.
Tom

[Don Moyer]

Tom,

Your understanding of the "R" terminal connection is right on. In recommending removal of the "R" connection almost 5 years ago, FACET's concern was/is that at the instant the starter switch is released, inductive feedback from the coil in the starter solenoid can periodically cause the fuse on the other side of the oil safety to fail.

We also strongly urge everyone using one of FACET's current line of pumps to follow their other recommendation, which is to use a 5 amp fuse inline between the coil and the safety switch. I know that Universal never installed a fuse in that location and (since we use the same FACET part number as Universal) I have no explanation of how they got away with that practice, other than that the pumps of that era may have been less likely to short out internally than the ones in current use. While FACET pumps are quite reliable in general, you need look no further than earlier conversations in our Forum to see what happens to the power lead, cord connector, and the case of the pump itself if fuse protection is not provided.

Don

[ArtJ]

Thank you Tom and Don

My pump has I believe, a 10 amp fuse which was installed back a number
of years ago when Don and I were trying to Isolate facet fuel pump issues.

It has never blown, probably because of being 10 amps vs 5 amps.
The R terminal was connected on the pump side of the safety switch.

How does the pump, without R terminal power, get around not being ran during starter operation?

Isn't this necessary to help the pump initially prime the fuel line during
cranking? I have always heard that electric pumps don't self prime well.

Thanks again

Art

[Don Moyer]

Art,

Most oil pressure safety switches close at 10 psi or less on rising oil pressure (ours close at 7psi), which means the switch will close within seconds of starter activation. This makes the "R" connections almost irrelevant.

Early model Prestolite starters don't even have an "R" terminal, and there never seems to be any issue with regard to electric fuel pumps causing hard starting within the early model fraternity, with the possible exception I suspect of the first start after a layup when all fuel may have evaporated out of the carburetor.

Don

[thatch]

Question for Don

Don,
Thank you for clearing up some of these "old to new" conversion questions.

Since I will most likely be converting from my early style electric pump to a "fuse protected" Facet pump in the near future I would like your input on the best way to prime the carb after a rebuild or fuel draining for other purposes. I know that many people use a squeze bulb for priming but I would like to know if others have created sort of a manual "R" circuit override to use the fuel pump for priming. If I took this route I would most likely use a momentary contact, fuse protected switch located outside of the engine compartment (for saftey reasons) so that it could not be left on accidentally.
Any thoughts?
Thank's again,
Tom

[Qben]

I have just jumped between the terminals of the oil pressure safety switch for a few seconds with the ignition on when I've needed to prime the fuel system.

Perhaps not the safest practice, but I always make sure to have the blower on and check for signs of fuel. Also, my oil pressure safety switch is located some distance away from any fuel sources on a bulkhead attached to the Indigo oil filter kit.

Qben Oliver

[Don Moyer]

Tom,

There're lots of approaches, I'm sure, but my favorite way to "manually"
operate an electric fuel pump on a boat is to connect a remote starter switch across the terminals of the safety switch. Then with the ignition switch in the "ON" position, you can operate the pump by depressing the button on the hand-held starter switch. In case you haven't seen one of these hand-held starter switches, they're usually connected between the big battery cable and the "S" terminal on the starter solenoid to operate the starter from the engine compartment.

In fact, as long as you have your "R" connection intact, you can connect the hand-held starter switch between the big battery cable and the "R" terminal on the starter solenoid to run the fuel pump without even having the ignition switch on.

Don