My guess is a grounding issue somehow.

 

So I am guessing the stock blinking on/off to get to the lower voltage of your on all the time 8.5 volts.

Did you run a jumper wire from the powered wire to the sender and not hook up the ground to see what happens?
Are you sure you are hooking the wire to the right stud on the sender?
Could the voltage of 8.5 be to high for the sender?

On my other project in the factory service book it gives how to test the fuel gauge using resistors.
I would figure what the empty / half / full resistance is and using resisters to test the gauge workings.
I would think if that did not work out right the gauge is bad.

Oh I did look over the links and there is nothing to hooking it up so I am at a lost??
Dave ----

 

 

What if you run a ground wire from the gauge to the tank sender so they are both grounded to each other.
Just pulling things out of the air here LOL
Dave ----

 

 

Okay, the Equus wiring diagram shows only a single wire to the sender. However, the sender shown at Rockauto has two insulated terminals, so I'm assuming (Danger! Danger!) your second wire is the sender ground?

If so, where exactly is this wire grounded? I like Dave's suggestion to run a ground jumper up to the ground point at the gauge. If that wire is attached to the cab, the cab itself may not be properly grounded. A jumper between the two points may clear it up.

Do you have an electric in-tank pump or anything else electrical at the tank? If the tank sits on rubber strips, the tank itself may not be properly grounded. Add an electric pump or who knows what, and now not only is tank not grounded, it has an electric potential above ground. My head spins thinking of the possibilities, but something like that could give you grief.

Please help me understand the sender. Set your multimeter to read ohms. Is there any continuity (less than 1 ohm) between the sender body and either insulated terminal? The way I'm thinking, there shouldn't be any, but I'd like to confirm this.

The gauge gets its power directly from a 12v source, right? If so, the previous discussion about the IVR doesn't apply at all. That means the only part of the circuit relevant to an 82 F150 is the tank and sender. None of the other wiring in the circuit follows the 82 wiring diagram.

The 8.5v you're reading at the sender? Don't worry about it. The meter is connected in series with the gauge. The resistance of the gauge is so deliberately high (this intentionally limits current flow through the sender) that the meter skews the current flow. I could bore you to tears with details of how a circuit behaves under test, but the short story is that isn't a valid test so don't worry about this seemingly misleading value.

 

 

I'll try to answer your questions, please disregard my ignorance.

Correct, the second wire is the ground wire for the sender. I have it attached to the vehicle frame. Its a good clean ground.

No, the fuel pump is mechanical, located in the engine block.

I will try this when I get a chance. Are you saying to test ohms on the terminal of the sender and the terminal on the gauge? I'm a little confused.

Yes, I believe you are correct. The only '82 specific parts are the tank and the sender.

Okay this is good information. I was pretty confused about this.

 

When you say two insulated terminals, you are referring to the terminals on the sender unit, correct?
I don't believe the arm rests on the bottom of the tank when empty. But even if it did, when there is fuel in the tank and its floating, the gauge is reading empty.

 

Let me make sure we are talking about the same thing. On the sender you linked at RockAuto, I see two insulated terminals. I'm not concerned with the terminals on the gauge for the moment, just the sender.

With the sender removed and sitting on your workbench, fire up your ohmmeter. Select a range of about 200 ohms, or something close. Test the meter by touching the leads together. The meter should show good continuity, usually just a fraction of an ohm for the test leads.

Connect one lead to the body of the sender. The flat ring (the mounting surface) is a good place. Connect the other lead to one of the insulated terminals. I'm thinking there should not be any continuity. Cycle the arm up and down but I'm still thinking the resistance value should not change, but am not positive.

Next, keep the first lead on the sender body and move the other lead to the second insulated terminal. Cycle the arm again and it should not change, if I'm thinking correctly.

After that, put a meter lead on each of the insulated terminals. Cycle the arm up and down and you should see the value change to reflect the fuel level.

Anyways, that's how I think the sender is wired. Can you please take a few minutes to confirm this?

 

Yes, I will bench test the OHMS on the sending unit when I get home. The factory sending unit is supposed to be 73 full-10 empty +/-.

 

Equus 7361 Details Fuel Level Gauges

• Range: Empty=73 Ohm, Full=10 Ohm
  • Compatible with most Ford and Chrysler Senders
    • Back-Lit illumination for night use
      • 90° Sweep
        • Rear twist-on ring mount design makes mounting simple Installation adapters sold separately
          

        Specifications:

        Manufacturer's Part Number:7361
        
        
        I wonder if you have one of them not most sending units?
        Dave ----
        

 

Back up in this thread, you guys were mixing up the factory setup with his aftermarket setup. No IVR and no blinking voltage in his setup.

I would say 8.5 volts is normal. You are going to have some voltage drop through the gauge. Even though this is a aftermarket setup, it generally works the same as the factory units, 12v all the time to the gauge, the sending unit varies the GROUND to the gauge, making it read the correct level. Since you are reading voltage on the GROUND wire, 8.5v is probably correct, and is also why it works when out of the truck.

The only difference I see being in the truck or out of the truck is grounding. I may have missed it if you already did this test, but I would still ground the sending unit out of the truck and see if it fails to work correctly. If it works correctly being grounded to the truck while holding it in your hand and moving the float, the only other thing I can think of is the float is not floating properly.

 

I was just pointing out how the stock setup works with the hope someone would see something and say "Hay you need to do xxxxx".

I would think you are right on the after market gauge and how it works. I am thinking it has an internal IVR made from electronics to drop the volts and why it does not blink like stock does.

I think he did test it out of the tank / truck and it worked so he put it back in and got the same "no work" thing.
I would like to know how he gets this to work just because as there is no reason why it should not.


Dave ----