factory fuel guage to aux fuel cell

[Thornton]

I've got an aux. fuel cell in my 71 that is my one and only fuel tank. I'm not sure who the manufacturer is, it came as part of a package deal on a bunch of parts and a 40. I'd like to use the oem fuel guage with it. It's hooked up now and it constantly reads 1/2 a tank. I notice that Downey has a 6 volt drop for their aux tank for a 64 to 72. Would this work or does anyone have any suggestions on what to do.

 

[alkarich]

Is your float level correct? Did you install this sending unit? Might be worth checking this first. I run both my tanks with the stock gauge.

 

[mustardfj40]

I've got an aux. fuel cell in my 71 that is my one and only fuel tank. I'm not sure who the manufacturer is, it came as part of a package deal on a bunch of parts and a 40. I'd like to use the oem fuel guage with it. It's hooked up now and it constantly reads 1/2 a tank. I notice that Downey has a 6 volt drop for their aux tank for a 64 to 72. Would this work or does anyone have any suggestions on what to do.

Can you please post more info on this Downey "6 volt drop"?

All can say is to run the same year of fuel senders front and rear...I have a stock '75 sender in the front and a late 60s sender in the AUX tank and my AUX can only register 1/4 even it's filled up.

 

[alkarich]

I'm running the same year senders in my tanks. But I think the old Conferr tank is deeper than the depth of the stock float.

As a side note, I originally was going to install a OEM aux fuel gauge on my dash pad. It came out of a 75 series pickup/ute and has the same molded housing as the old 4Runner altimeter/inclinometer. Pretty nice item, ended up on Ebay.

 

[Coolerman]

From old MUD posts:

Here's the deal; 9/72 and older gauges/senders work this way:

110 ohms empty
3 ohms full
and with a 7 volt drop built into the sender (a full 12 volts will instantly burn out the gauge).

9/72 and newer gauges/senders work on
120 ohms empty
17 ohms full
and do work on a full 12 volts.

Most (not all) aftermarket gauges work on 240 ohms empty, and 33 ohms full.

 

[mustardfj40]

From old MUD posts:

Here's the deal; 9/72 and older gauges/senders work this way:

110 ohms empty
3 ohms full
and with a 7 volt drop built into the sender (a full 12 volts will instantly burn out the gauge).

9/72 and newer gauges/senders work on
120 ohms empty
17 ohms full
and do work on a full 12 volts.

Most (not all) aftermarket gauges work on 240 ohms empty, and 33 ohms full.

Has anyone tried to add an 10 ohms resistor to make the old senders compatible with the newer gauge? Thanks.

 

[Downey]

That was my old post. The problem is not simply that Toyota changed the ohm values at 9/72, but they also changed the volt values, and this gives us fits when a guy wants to run both tanks off a single dash gauge using two different sending units. Originally we thought the 9/72-older senders had a 6 volt drop. One of our customers installed a 6 volt drop and his gauge read correctly. Subsequently TMS got us some information from Japan and evidently the stock sender actually has a 7 volt drop. This means you could use your stock front tank with pre 9/72 sender and dash gauge, combined with a post 9/72 Toyota sender or Downeys digital sender "IF" you put a 6 or 7 volt drop on the rear sender wiring----make sense????

 

[Thornton]

Thanks for the responses from everyone.
Jim, what you say somewhat makes sense. One thing is that I'm only running the aux tank. No stock tank at all in the truck. I extended the wire from the old sending unit to the new one. I know almost nothing at all about automotive electrics is there some way to test the sending unit in the tank that I have to see what it is.