2007 Toy Hauler Fuel gauge help

[Derby6]

Unit is a 2007 Desert Fox. Old fuel gauge filled with water and I replaced it. I swear I wired it the same (just had to use splice plug ends vice loop ends) but fuel gauge shows full; even when its empty. Been googling but can't seem to find info on one with as many wires as mine.
1 red (hot), 1 Black (Ground), and 3 white. Backlight for the gauge has additional 2 wires.
This is how it was wired:
- Red to positive (+) pole with backlight red (hot) wire also connected
- Black to Ground (-) pole
- 3 Whites and the backlight Black (Ground) wire all connected to the sending pole

There is an on off switch on other side of camper that is working--When its off no power to the gauge.

Now with new gauge backlight is on and always shows full.

I disconnected the 3 White wires and the backlight Black (Ground) wire all connected to the sending pole and played with them individually.
- 2 of the white wires did nothing alone or together or with the Light Black (Ground) wire when connected to the sending pole.
- 3rd white wire makes gauge show full and when the Light Black (Ground) wire is connected light does come on. But I found the fuel pump would not come on.
- So with the 3rd white wire and 1 of the other 2 white wires the pump works.

Side note. I connected the Light Black (Ground) wire to the Black to Ground (-) pole and assumed light would come on but it didn't...

I pumped about 17 gallons out and tank was empty. So I dumped about 4 gallons back in so gauge should be reading some but less than a 1/4 tank.

I'm so confused. Have no idea what one of the white wires do? And why the gauge won't work. And from this post you can tell I am far from an electrician....

 

[TheBar]

I've never heard of that many wires on a single gas tank system.

I would guess you have grounding at the sending unit on the tank or a break or corrosion at some connection between the tank and dash. Since you had water in the gauge I'd start looking under the dash.

You could buy a tone generator and connect to each wire at the gauge to see if they have continuity all the way back to the tank.

Finding someone with gas gauge wiring knowledge won't be easy. A hot rod shop might be willing to help you. They have to make custom gas tank and dash setups.

Alternatively you can buy custom gas tank gauges and matching sending units. The sending unit has to match the gauge resistance which would be tricky for a non-electrician to figure out.

 

[Rene T]

I take it you didn’t take a picture of it before disconnecting
Are you sure the white wires were indeed hooked up to the gage

 

[Derby6]

Lol yea I normally take a pic but this was so easy and straightforward I didn’t.
I am sure they were all hooked up.

 

[Derby6]

Gauge is outside. Gauge resistance might be it. Of course when I did it weeks ago it lit up and went to full so I thought it was Good to go and tossed old gauge.

 

[Kirk]

Do you know what type of sending unit you have? It really doesn't sound like it is the typical float level sensor. The sending unit usually uses a float connected to a potentiometer but I'm suspicious that you have something different.


A typical automotive type fuel gauge has three or four wires.

"S" or "Send" terminal: This connects to the signal wire from the sending unit.

"I" or "Ignition" or "Pos" terminal: This connects to a switched 12V power source (like the ignition switch) to power the gauge.

"G" or "GND" or "Neg" terminal: This connects to a good ground source.

"L" or "Light" terminal: If the gauge has a backlight, there will be a separate wire to connect to a power source for the lighting circuit (like the dash lighting circuit).

 

[Derby6]

I don’t Kirk.