Tan/lt grn wire/Fuel Pump Relay

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I am starting a new thread on this because I totally agree with Stan's post to me. For those that may look in the archives at this, the original problem is a 1988 Mercury Grand Marquis, with a 302 fuel injected engine. I
had tuned, and maintained the car to prepare for my trip across the US, with all the normal parts. New spark plugs, wires, distributor cap, rotor, fuel pump, new drive belt, new tires, etc.. It ran like a dream all the way across. Three days after I reached my destiny, it would not start one morning.
The battery was drained. When I charged the battery and started jiggling wires, the wires attached to the fuel pump relay kept referring a clicking noise to somewhere down in the center of the engine compartment. Still don't know where it was coming from. I checked all wires and wrapped any that were questionable. I also replaced the EEC and Fuel Pump Relay to be on the safe side. And, by that time, the older battery had been drained one too many times, so I replaced it also. Whatever it was, it was causing a drain on the battery without any key in the ignition. So, it was a constant drain.
In any event the fuel pump will no longer start on it's own. If I ground the tank and hotwire the relay, I can force it to turn on. A whole lot of other things have happened in between. You can read about them by searching "won't start" on this NG.
I started this new thread because Stan sent the NG a post today that I think gets to the real crux of the problem. I agree with Stan. I do not think that the tan/lt grn wire coming out of the relay is working the way it should. And I think that following it will eventually take me to my problem.
This is my understanding of the fuel pump relay circuit on this car. (By the way, I did understand the majority of this circuitry all along.) There are two circuits to the fuel pump relay on this particular car. The yellow to orange wire circuit is like a gate. The yellow wire is coming in and carries 12 volts at all times. It is called an 'always hot' wire. There is an internal 'gate' on this circuit that 'rests' in the open position when the car is parked and off. The outcoming wire of this circuit is orange and it goes to the inertia switch (turns off in case of an accident) in the trunk, and from there to the fuel pump. That outgoing wire only has voltage running through it if the gate is closed. The second circuit is the red to tan/lt green wire circuit. The red wire is incoming and inside the relay on this circuit is a magnetic coil. When the voltage flows through this circuit, it activates this magnetic coil and magnetizes the gate on the yellow/orange wire circuit to a closed position. This allows the orange wire to feed volts eventually to the fuel pump and turn it on. That is one of the things that is not happening in this car. The fuel pump is not getting turned on.
I have tested the relay to make sure it is working properly and it is (this NG carries the instructions for that). I have tested the socket, and I believe it is not working properly. Although I think that Thomas disagrees with me. If I jumper the yellow to orange wire in the socket, I can force the fuel pump to run. So, that tells us that the inertia switch and the fuel pump connections are working properly. When I test the red to tan/lt green wire, I believe it is not doing what it should be doing.
Voltage does enter on the red wire. I get 12 good solid volts on the multimeter. But, at no time (key off, key in 'on' position, key in 'start' position) is there any voltage reading on the tan wire. It does not get a starting blip or anything. That seems totally wrong to me. I would think that even if it is nothing more than a grounding wire (and it really isn't JUST that), then I would get an outgoing volt blip on the meter. The tan/lt grn wire that is outgoing on the fuel pump relay actually goes to the EEC-IV connector and gets coupled with an identical tan/lt grn wire. This page shows you this connector as the Fuel Pump Connector: http://www.shotimes.com/SHO3eeccodes.html
According this write-up grounding this connector will run the fuel pump continuously. That is not happening. So, I absolutely agree with Stan. I think I have to track down the cause of this circuitry not functioning properly. I have changed the fuel pump relay three times, to no avail. And the relay has been testing using a procedure described here in this NG. It is working properly. I can not find a replacement socket that is correct. My local Napa place has one, but the gauge of the yellow and orange wires is much smaller. I don't want to cause further problems by causing incorrect impedance.
That's it. I don't want to stray from anything other than this circuit and what might cause the self connector to not allow the pump to run continuously or what would cause that tan/lt grn wire to not at least have an outgoing blip on the meter. If we keep it down to just that topic, I think we can solve at least that problem and get the fuel pump to engage properly.
Keep in mind a these things: The yellow to orange wire circuit is working properly. The relay has been tested and works properly. There is 12 volts coming into the relay from the red wire.
Thanks for all your patience and suggestions. Take Care, Sharon
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I think I have figured out a way to test socket of the tan/lt green wire. I need to make some external connectors from that socket, since I can't find a correct replacement socket. I have already cut the wires hoping to find a replacement, but I couldn't. So, can I put slip on connectors on those wires and put them on the relay, taping the crap out of them so they don't arc? Starting with the yellow wire first so that it is properly insulated since it is always hot. Do you see a problem with this thinking?
Thanks and take care, Sharon
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There is nothing wrong with not using the socket. If you want to just crimp on new terminals, get terminal that have shrink seals. That way you don't have to use tape. It is a much better and will prevent future problems.

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I either missed it or you did not mention you had the pump replaced......at any event lets move forward.

This could be a coincidence, of just a bad battery, but again, moot issue.

Lets assume we are at square one with no prior posts. Does the fuel pump run with just the jumper wire installed and WITH OUT the extra ground you installed? Also, when you "force" the pump to run, will the engine run?

This is where you do not understand. That is a ground, and the ground is made by a transistor in the engine computer. If the ground is made you will not see voltage on most meters. Some you might see 1 volt. Now if the ground is not made you should see source voltage ( 12 volts ) if you do not then you have only two possibilities. 1) the relay terminals are not making contact in the relay socket. 2 ) the relay coil is open.
Now it has been explained to you as to how to test the tan wire. I'll go through it again. If you do not understand please say so.
The tan wire will be called a circuit, because that is what we are testing. Make sure your batteries are installed correctly. Set your meter for ohms. Question, is you meter an auto-ranging meter?
A) Key off. B) Remove the relay. C) At the relay socket, find the terminal for the tan wire. Probe the terminal with a test lead. D) put the other test lead to a good ground.
You should see infinity. ( very high resistance )
E) Have some one turn the key to start and keep it there long enough for you to get a reading.
You should see about 5 ohms or less.
<snip>

You need to have a little more understanding of DC electronics. And what is happeing.

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The tan wire is a just ground wire. Look at the schematic you posted. You will see it goes the eec self test connector and engine computer. Look at the eec self test connector, it's just an open connector nothing more. The wire stops there. The only time it is used there is when some kind of test equipment is installed and that equipment needs to run the fuel pump. It makes ground energizing the coil in the relay. That is what the engine computer does. It just makes ground nothing more. The engine computer makes that ground only when required. It makes that ground only when it sees a crank signal and briefly when you turn the key to run. That has been explained at least once by me and at least once by some one else. That is how the ignition module became part of the discussion.
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I took the connectors out of the plastic socket. I spliced in two new shrink wrapped connectors for the larger wires (orange and yellow) and used the original connectors for the smaller lines because their nipples were too small to adapt to a 'normal' connector. On these, I tightened the slot and taped, taped, taped each with electrical tape to avoid any arcing. I also put a new connector on the self test module just to make sure that the tan/lt grn wire had a good connection there. I turned the key to on, and did not hear the pump. I turned the key to start, no pump.
I believe I need to keep following that wire down the line. Since I have 12 volts coming in on the orange wire, and twelve volts coming in on the red wire, the only thing that I can think of is that the tan lt/grn wire (grounding) is not allow the circuit to complete and allowing the electro-magnet inside the relay to work properly. Keep in mind these things: I tested the relay, using the car battery (read this NG for details), and it works correctly. I have now rewired the relay connecting wires with new or tightened connectors, ruling out a bad connection in that area. If I am wrong on any of the procedure I have completed here, please let me know.
I am ready for the next step of checking this wire and circuit. Let me reiterate, Thomas, what you said yesterday, and ask a couple of questions: Set your meter for ohms. You asked is your meter an auto-ranging meter? My reply and question: I am not understanding what an auto-ranging meter is. I can tell you that there are only two setting for the ohms on the selector. One is RX10, one is RX1K. And the needle scale for ohms goes from 500 to 0. A) Key off. B) Remove the relay. C) At the relay socket, find the terminal for the tan wire. Probe the terminal with a test lead. My question. By this, do you mean attach the + side of the multimeter to the tan/lt grn wire? (keep in mind that I can now check the wire directly, since there is no more socket). D) put the other test lead to a good ground.
You should see infinity. ( very high resistance ) My question: Is this without inserting the key in the ignition?
E) Have some one turn the key to start and keep it there long enough for you to get a reading. You should see about 5 ohms or less.
Thanks for helping me through the next step, by answering the questions and giving me a little clarification. Take Care, Sharon
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An auto ranging meter has only one OHM setting. Set your to the lowest level. That would be RX10. It really does not matter what lead to attach to what part. But I'll say put the positive on the tan wire.

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part.
terminal.
I get a reading of 7 on the Ohm scale at the top of the meter.

you
I get a reading of 10 on the Ohm scale.
Just to let you know that I am looking at the right markings, Ohm scale on my meter is at the very top, like this one: http://www.homedepot.com/prel80/HDUS/EN_US/shop_cart/pg_alt_view_popup.jsp?C NTTYPE=PROD_META&CNTKEY=shop_cart/pg_alt_view_popup.jsp&BV_SessionID=@@@@143 0444221.1069174288@@@@&BV_EngineIDceadcjmehmdhecgelceffdfgidgjl.0&MID7 6&prod_id00180&DRC=4
Can you tell me if these readings tell you anything about how to proceed Thomas. And thank you for answering my questions. Take Care, Sharon
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Here is a clear picture of the meter. I will let Thomas tell you how to use it.
http://home.ptd.net/~stankt3f/GMT-19A.jpg
Stan

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Thanks Stan, but it is a little different. Just so that Thomas can see what scale I have on mine and what setting I used, I loaded a pic on the web here:
http://www.rare-cancer.org/car/meter.jpg
The meter is set to the setting that I used and the readings that I quoted are from the green upper scale with the Ohms mark. Just wanted him to know that I am doing this correctly. Thanks and take care, Sharon
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Your meter does not have the range to properly test a transistor. I can not trust any of the values it would give. To 0 that meter turn the slot next to the Electro-Tec.
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not
to the
I did calibrate it, according to the instructions you just gave me. I set it to RX10, touched the leads, moved the calibrating knob until it just touched the 0 mark. Then I did the test, without touching that knob again.
Take Care, Sharon
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Just did it from scratch again, and it is pretty close to the same reading. Started with calibration. No key - right around the 3 mark, key in on positions, it dips down a little, key in the start position, it goes up to right around 5, then when turned off it is right around 3 again.
Take Care, Sharon
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With those "readings" the relay should be "on" all the time you have 12 volts to the red wire, yet you say the pump does not run?

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Yes, the pump does not run. But, keep in mind that I got that reading WITHOUT the tan wire hooked up. And without the yellow and orange wires hooked up. I have wondered all along if there is something that is causing that tan wire not to ground properly. It travels from that relay to the self tester through the firewall near the steering column, as far as I can tell. It does not get grounded anywhere in between onto the body of the car.
That tan lt/grn wire goes to the engine control module, according to the wiring diagram I have. And that is in the dash, behind that firewall, near the steering column. Right where the engine control module is mounted. I am not sure if it does anything there other than ground. Can you tell me?
I ask this question because I was wondering if I can possibly test this out by NOT connecting the tan wire to that relay and just connecting the other three wires. Then check the volts on the nipple for the tan wire. Is that a possibility? Or will not having that ground, with the other wires hooked onto the relay, cause damage?
Thanks Thomas, Take Care, Sharon
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You are not looking for anything but continuity. It does not need to be hooked to anything but the tester.

Being that is not part of the circuit, it does not matter.

That is correct.

I've already told you , it only goes to the ECM and EEC self test connector. Look at the schamatic, it is correct.

I have already lead you through that test. You claimed there is 12 volts there.
"Sorry Thomas, I had another situation to attend to. I checked the volts on the red wire in the start position. On my scale, it reads a little over 12+ volts coming through when I put it on the 10 setting. That would be reasonable. Then I connect the red wire to the relay, put the positive lead on the tan wire and put ignition on start. I show a little over 12+ volts all the time I am cranking. I hope that helps you to see what it is doing.
Thanks sooooooo much for trying. Take Care, Sharon"
Now here is what we have. 12 volts to the relay on the red wire. good condition 12 volts through the relay coil with no ground attached. good condition You claim that you can jump the yellow and orange wire the pump runs, and you are even able to smell fuel, proving the pump circuit is good. With all wires installed to the relay, and when the original relay socket was in place you have 0 volts on the tan wire indicating a complete circuit, meaning pump should run. Even though you are not using the correct meter, you have what appears to be a good ground, although it appears to be making ground all the time. So If all is "hooked up" correctly, that relay should turn on the pump as soon as you turn the key to run. Yet you say that the pump does not run.
So what does that mean? If the relay is installed correctly, every time your turn the key to run, the pump should come on. What can be wrong? Relay not installed correctly. Wire gong to wrong terminals. Bad relay. Misunderstanding of what you are seeing and doing resulting, because of that giving incorrect information back to us.

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Thanks Stan.

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You should be using a digital volt ohm meter for this. From that picture, I can not see what scale is what. The best thing to do is go to Radio shack and get a digital meter, they are very inexpensive, and you do not run the risk of false readings and damaging the electronics you are trying to test..
6&prod_id00180&DRC=4

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I can

get a

false
This is an automotive multimeter. Here is another pic of the actual meter I am using, not the one that Stan published. I have no difficulty reading this scale. And I tried it several times to make sure that it was constantly registering the same reading. The green upper scale with the ohm symbol is what I am reading, and as I said before it is set on RX10:
http://www.rare-cancer.org/car/meter1.jpg
Hard to get to a Radio Shack that is over 30 miles away when you don't have a car. LOL
Take Care, Sharon
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Yes I know it is called an automotive multimeter. It is not the meter you use for testing the electronics in a computer. It's fine for checking voltages in non-sensitive things like wires, but not for electronics. It does not have the range or accuracy. Example, If I wanted you to check the voltage drop on the alternator ground circuit, I would want you to look for .10 volts. You can not do that with this meter. I would much rather have you use a test lamp to see if the ground is being made or not. In fact it would be better because it is a go-nogo test. Light on it works. No light no work. And again, not just any test lamp, but one designed for use on electronic equipment.
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