Please Help! No fuel gauge or map lights. Need diagrams

[SportTrack05]

Hello. Just introducing myself, I have a 2005 sport trac that has been great to me for the past 2 years. It has 189xxx miles and has been used primarily as my tow/ daily vehicle.

As of a couple of months ago the fuel gauge would bounce around and just die below the E mark with the LOW FUEL being displayed on the message center. At the same time i would loose the gauge i would loose the map lights (noticed one day stopped looking for something) and when the map lights would work so would the gauge.

Ive changed/ Replaced:

Checked fuse #25 (dome lights still work perfect)

Cluster (tach and speedo started acting up a month after the fuel gauge stopped reading) 60k like new working unit

Fuel pump assembly Twice
First time was with ebay brand second time with brand new motorcraft (changed it the second time cause i thought the ebay brand might not have been compatible with gauge and just wanted to eliminate doubt)

I went through all connectors and checked to see if they are loose and or corroded. (nothing found bad or damaged)

I back fed the map lights jumping it with the dome light wire next to it and i had map lights and never blew the fuse.

I have a feeling that the power source for the map lights and fuel gauge come from or ground to the same place. I need a diagram to be able to find out whats going on. I talked to a buddy at ford and he told me that i might be the smart junction box. I want to test before i fork out anymore money as I'm already $500+ into this ordeal.

Sorry for the long post, and thank you.
-B

 

[DevinOB]

You could try removing the smart junction box and inspect the conectors for corrosion. Maybe you have some water getting into it from a leaky windshield seal. I will try and bring up a diagram on your fuel sending unit circuit today and see if there is a common ground with the map lights and get back to you.

 

[SportTrack05]

Where is the smart junction box located? I was looking for it yesterday and couldn't really find it. Im sure the fuel gauge and map lights all stem there. If i had the diagram i could at least find the wires and test right out of the junction box

Thank you again i really appreciate it.

 

[DevinOB]

the central junction box is located on the left side of the dash. you should be able to gain access to it by removing a panel on the side of the dash with the door open. It looks like it receives a vpower signal from the battery saver relay(auxiliary relay box 2) and will be a light green and orange wire (pin 1 on the instrument cluster connector)( pin 2 on the fuel pump connector). Signal return/ground for the fuel sender is a black and orange wire and is grounded in the instrument cluster(pin 22 on the cluster connector) vref for the sender is supplyed by the pcm and will be a yellow and white wire and is pin 21 on the cluster. There is a microprocessor in the cluster that acts as a delay circuit to prevent the fuel gauge needle from bouncing around but you have already replaced the instrument cluster correct?

Hope this helps.

 

[SportTrack05]

Just for clarification. Vpower is 12v battery power, Vref is 5v?

The delay circuit in the cluster is working just fine because the needle rests on E and after like 60 seconds dips below E and says low fuel on the message center.

Do you have a pic of the SJB or a blow up of where it is? the only thing on the left side behind the panel is the fuse box. Right now everything needed to put a cluster in is out so i have access to everything

 

[DevinOB]

Sorry for the delayed response, I was having some computer issues. Vpower (lg/og wire) should be battery voltage and Vref (ye/wh wire) should be 5 volts. The fuse box on the left side of the dash is part of the central junction box. If it were me and you have access to a resistance and voltage meter I would want to check: 1. Resistance between the instrument cluster and the fuel sending unit on the vref and ground circuits, 2. Make sure I have 12 volts at the sending unit on the lg/or wire.

If those tests are good you could install a jumper wire on the fuel sender\pump connector on the yellow and white wire(vref) and the black and orange wire(ground) and that should make your fuel gauge in the dash read full. If it does not then you know your instrument cluster is bad.

Note: when jumping the pins on the pump connector you may have to wait up to 30 secs for the gauge to move to allow for the delay circuit in the instrument cluster.

I was also wondering if your tach and speedo are still acting up or did the "new" instrument cluster fix that?

 

[SportTrack05]

Sorry for the delayed response, I was having some computer issues. Vpower (lg/og wire) should be battery voltage and Vref (ye/wh wire) should be 5 volts. The fuse box on the left side of the dash is part of the central junction box. If it were me and you have access to a resistance and voltage meter I would want to check: 1. Resistance between the instrument cluster and the fuel sending unit on the vref and ground circuits, 2. Make sure I have 12 volts at the sending unit on the lg/or wire.

If those tests are good you could install a jumper wire on the fuel sender\pump connector on the yellow and white wire(vref) and the black and orange wire(ground) and that should make your fuel gauge in the dash read full. If it does not then you know your instrument cluster is bad.

Note: when jumping the pins on the pump connector you may have to wait up to 30 secs for the gauge to move to allow for the delay circuit in the instrument cluster.

I was also wondering if your tach and speedo are still acting up or did the "new" instrument cluster fix that?

Update:

The lg/og wire had a faint false 12v with the connector off it must be corroded or open somewhere. It was enough to fool my meter but not enough to even make my test light come on. Once there is any load on the wire it it drops the voltage to 0. I ran a new wire off an ignition open fuse in the main fuse box back to the Red - Lg/og wire ( depending where connector is). The minute i did that i had map lights and my fuel gauge back.

5 weeks and 2 shops and i ended up fixing it myself. Thanks again.

 

[DevinOB]

Awesome good to hear. I was wondering if you ever got it figured out. Thanks for the update.