F250 Schematic?

[brians]

Anyone got the schematic for a 1984 F250 4x4 that they can post? I'm having trouble with the fuel gauge. I swapped out dashes (with towcat's help) and attempted to trace the wires but something is still wrong.

The gauge moves slightly, hovering around E, even though both tanks are full. Switching tanks makes a slight difference.

BTW, we added an instrument cluster with a tach in it. Works great. It's nice to see the RPM's.

Thanks in advance.

Brian

 

[highest_vision]

I'd be willing to bet your senders are shot. Get yourself an average sized relay, or maybe a headlight, unplug one of the senders, and use the coil side of the relay or the light bulb to take the place of the sender. This should make the gauge read full. Or fuller. 10 ohms empty, ~78 ohms full.
James

 

[Agnem]

There are schematics in the Moose Truck Album.

 

[towcat]

I'd be willing to bet your senders are shot. Get yourself an average sized relay, or maybe a headlight, unplug one of the senders, and use the coil side of the relay or the light bulb to take the place of the sender. This should make the gauge read full. Or fuller. 10 ohms empty, ~78 ohms full.
James

james-
I sent Brian under to pull the FSV plug and jumper the terminals on the plug so the needle on the gauge to go to a full reading. No change. This was also done as per Furd's diagnostic procedure in the service manual to determine if the sender has issues or if the wiring has issues. After two heater pannel feul switches, and one gauge pannel, I can safely say there is a problem somewhere in the wiring. besides, Brain is a ****** for chasing down issues in the wiring.

 

[The Warden]

Brian, I don't have anything I can post, but I've got the '84 FSM's sitting in the halfcab of my truck. I think there are wiring diagrams in there, but can't say for sure without looking. If you want to take a look, let me know...

 

[highest_vision]

85 diagram shows yellow/white wire from switching valve up to gauge. Same for both tanks. It appears that (at least for 85 models) you would want to ground this wire, not jump it to another. If I remember correctly later models are different, maybe 84s are too!
James

 

[highest_vision]

Here's a snap of the diagram. You can see where the tanks' senders share a common ground at the bottom.

 

[brians]

Gang,

Thanks for the quick responses! Armed with a schematic I can take a closer look at the wires and see if I can see what's wrong. In the worst case, I can re-wire the circuit from top to bottom.

Since both of the senders share a common ground that seems like the most obvious place to begin troubleshooting.

I'll also check the resistance of the senders and see if I get ~78 ohms since the tanks are currently full. It's possible both senders are bad. Is this a common Ford problem?

Brian

 

[Agnem]

It would be a suprise if both were bad.

 

[Freight_Train]

did you use the same year or style of Dash or did you upgrade to a newer style dash?If so,there was a change in senders around the mid IDI run.

 

[brians]

I upgraded the '84 cluster with an '85 cluster but the problem was identical with both clusters.

Brian

 

[highest_vision]

Did the senders quit working simultaneosly? If not I would not be surprised to see them both be bad. Mine were both bad when I bought the truck and it isn't uncommon for them to fail. Just a printed circuit board immersed in fuel.
James

 

[brians]

James,

Althought I got the truck 2 years ago, I just got it registered. I did change out the front fuel tank and sender (thanks to towcat's 4 wheelin') since the fron ttank leaked but they haven't worked since I've had the truck.

Brian

 

[brians]

I thought I'd post my current process to date.

It seems the problem is a strange one. The hot and the ground have been reversed. I get 12 volts going to the fuel guage via the black wire and the yellow with white stripes connects directly to ground. If the reverse the leads the fuel guage works correctly. This is true of all the guages in the dash cluster. All the others work so I'm assuming only the fuel guage is polarity sensitive.

I haven't yet traced down the cause so I have more fun to lookj forward too.

Brian

 

[highest_vision]

Have you checked to see if someone spliced new ends on at some point and got the wires mixed up? Might end up tearing the wiring harness apart to find out what is going on but if you can simply reverse the wires and make it work, the wires are very likely switched at some point.
You don't have an extra battery hooked up, and hooked up backward do you?
James