Oil idiot light wiring question

[rderr]

Just got off the phone with EZ Wire tech line. I was asking about how to wire my 66 custom cab oil sender with an oil gauge and idiot light. He told me to basically wire them in series. Meaning 5V out of the CVR to the gauge then straight to the oil light then to the sending unit. This doesn't sound correct to me. This would put only 5V through the bulb if I had low oil pressure. Can someone please clarify this for me?

[banjopicker66]

That is ABSOLUTELY wrong.
Each indicator needs its own separate ground. Both the gauge and the light use a ground, but through different sending units. Further, these two do not use the same voltage.

This is how they work:
Light: The light sending unit is an ON-OFF switch. 12V Power is fed full time to the oil light, and from there to the sending unit. When the engine is not running, the sending unit grounds out the bulb's current. The current flows through the light, then the sending unit, illuminating the bulb. Once the engine is running and when oil pressure reaches the trigger point, the contacts inside the sending unit open, interrupting the ground for the light, and it goes off because it no longer has a ground to complete the circuit.

Gauge: The gauge's sending unit is a variable rheostat. It isn't ON-OFF but continuously variable. ~6V from the ICVR is fed to one side of the gauge, and the wire from the other side of the gauge runs to the sending unit. When the engine is not running, the sending unit has no ground, so no current flows through the gauge; it registers "0". Once oil pressure builds up, the variable rheostat allows some current to flow. Inside the gauge is a tiny wire that heats up, depending on the amount of current flowing though it. The more current as allowed by the sending unit, the more heat which means the needle deflects more. Less current, of course, means the wire cools, and the needle deflects back down to a lower oil pressure reading.

Again, BOTH sensors require their own voltage sources, and their own separate sending units. In this case, they use different voltages as well.

By the way, I am assuming you are using Ford original gauges, which are calibrated for ~6V. Other gauges or a non-Ford wiring setup might be different.
Hope this helps.

[rderr]

Thanks. You confirmed what I was thinking. However, my truck has but 1 oil sending unit and the light and oil pressure gauge always seemed to work before I took it apart nearly 2 years ago. I can't imagine the single oil sender tied to a 12V bulb as well as a 6V gauge would work right. I feel like I understand how it is supposed to work but I can't figure out how it worked before with just 1 sender. Could there be another sender in some obscure location other than right at the oil filter?

Thanks,
Rick

[Toyz]

Got my attention now! Were you originally using the factory light with an aftermarket gauge, or do you have the optional gauge package?
Paul

[banjopicker66]

On the 352, and I think on the 300-6, both sending units were on a "T" shaped plumbing arrangement out of one oil port.
The 352 had them down near the oil filter stand, and the 300-6 on the side of the block. 289s and 302s had theirs in the same location as well.
If I remember correctly, though, some of the Ford V8s have another oil port at the top of the engine in the back - I know my 460 does, but I do not remember if my 352 did.

There is no way one sending unit can serve both the light and the gauge. The gauges works completely differently from the light, and the sending units are matched to either the light or the gauge. Not both (or either, for that matter).

[SRSControls]

Correct me if I am wrong here Banjo (as I often am), but did not Ford, in their infinite wisdom, have oil gauges that were basically "go/no-go"?

For example, I used to have a '91 F-150 with the 300 I6 that had an oil gauge in the cluster. At some point the gauge stopped working. If memory serves I had to replace it with a new "oil switch" which basically read 1/2 to 5/8 on the gauge when the oil pressure was "good". I may be wrong but that is how I recall it. Maybe someone else can chime in here as well. Of course I know this has no relation to Slicks, but if I remember the situation correctly, maybe it was common practice on our slicks as well.

Respectfully,

Scott.

Edit: I actually found an interesting read on the subject and my suspicions were confirmed.

http://www.rowand.net/Shop/Tech/FordOil ... ugeFix.htm

Again, I do not know if this was applicable back in the 60's, but it is food for thought.

[Toyz]

You are absolutely correct; TMK, it first started with 70's T-Birds. I have encountered some slicks where that switch had been installed in place of the original sender.
Paul

[banjopicker66]

Well, this is very interesting!
I do not know how the pressure gauge works in the article you described, it is completely out of my experience. I would have to read a lot more to better understand it. Thanks for posting about it!

I can say, though, that it wasn't set up like this in the '60s. The gauges and idiot light work as I described. Apparently, the EZWire tech was looking at the later gauge wiring or switches, not the '60s.

If Rick's truck is using later gauges, it may very well be possible to wire it up as EZWire described.

What does this "oil switch" look like? I am familiar with the idiot light type, and I know the canister shape of the pressure gauge sending unit, but I am not familiar with this type.

[Toyz]

John, that was my question; not sure what kind of gauge/lamp combo he has nor how it might be wired, as well as plumbed.
Paul

[ICEMAN6166]

If I remember correctly, though, some of the Ford V8s have another oil port at the top of the engine in the back - I know my 460 does, but I do not remember if my 352 did.

my 292 has 3 i think on the drivers side, not sure about the passenger side
pretty sure the fe has multiples as well

[SRSControls]

Here's the switch mine took, it definitely was a switch and not a sender.

[bruceandersson]

If you do not care about the originality of the gauges, I'd go with a mechanical oil gauge. I trust them a little more than the electric ones. I've done nothing to my 66 and it does have both the light and gauge. I'll try to take a look at them tonight if the rain ever stops.

[banjopicker66]

Well, I learned something new.
I did not know that a single sensor can be used for both the gauge and the idiot light - I am having difficulty getting my brain around how it is done.

Oh well, thanks for the ride!

[rderr]

My 66 custom cab is bone stock (including original gauges). I wasn't aware that having idiot lights and gauges was considered the "optional gauge package" but if so, then that is what I have. I will need to do some more poking around when I have time and adequate light to see if there is another sender in my 352 engine bay. If someone could post a picture of their set up I sure would benefit from it.
Also, while I had the EZ wire tech on the phone I asked about the ALT idiot light. He told me to wire that bulb in series in the white Alt Exciter wire coming from the voltage regulator I terminal. I am not sure what the Alt Excite signal is or does but if it is always hot then wouldn't wiring the Alt exciter to both sides of the bulb make the alt light always on? If someone could explain that signal and the Alt idiot light wiring, I sure could use that help as well. I did see where someone posted in the hints and tips that he wired the Alt excite to the bulb but I can't remember exactly how the other side of the bulb was wired.

I appreciate all the help you guys have already provided. If you were closer the beer would be on me!

Thanks,
Rick

[rderr]

OK figured out that I do actually have two oil sender units. Question now is which one is for the idiot light and which is for the gauge? One is a larger canister looking thing and the other is more streamline almost like what I would call a switch.

Thanks,
Rick

[SRSControls]

Large canister is for the gauge.

[Toyz]

Wow, since my "Camper Special" gauge cluster has aftermarket gauges, i had forgotten, or never paid attention to, the redundant setup! Like John, I can not picture utilizing a series arrangement since when the switch is grounded, it would seem to affect the gauge reading. I think I would stick with independent wires; based mostly on my lack of understanding. As to the ALT lamp, what he is suggesting makes no sense to me; I don't believe the "I" wire acts to excite the system directly. That wire is in fact originally used for the lamp, in combination with a parallel resistor.
Keep us posted; this looks to be a learning experience at your expense!
Paul

[Toyz]

Moment of (potential) enlightenment! I wonder if his wiring identifies the white wire as such based on applications using an integral regulator, while for your application, it simply sends power to the regulator. There must be one of our members who has installed EZ Wire with original components!
Paul

[banjopicker66]

Also, while I had the EZ wire tech on the phone I asked about the ALT idiot light. He told me to wire that bulb in series in the white Alt Exciter wire coming from the voltage regulator I terminal. I am not sure what the Alt Excite signal is or does but if it is always hot then wouldn't wiring the Alt exciter to both sides of the bulb make the alt light always on?
Rick

The ALT idiot works just like that.
One side of the bulb is connected to the ACC stud on the ignition switch. This means that the bulb has full time power when the truck is on. If the other wire is grounded, the bulb lights up.

The other bulb wire is connected to the "I" terminal of the regulator. As long as the alternator is not producing voltage, the bulb is grounded through the "I" connection on the regulator, and so illuminates.

However, when the alternator is producing juice, the "I" also supplies 12V to the other side of the ALT bulb.
So yes, the ALT light has 12V to both sides, but the "I" terminal doesn't produce juice unless the alternator is producing voltage.
Once the "I" produces voltage, the bulb goes out - it has no ground.

Make sense?

[Toyz]

Rick, I believe the shunted resistor between the lamp terminals needs to remain in the circuit for the lamp to function. The increased charge voltage works with the resistor, causing the lamp to shut off.
Paul