The wiring diagrams I looked at for the two tank systems are confusing, I see two possible ways this is wired as follows:

Battery +ve---Ign sw---Fuel level indicator----upper tank level sender (0-180 ohm)---lower tank lever sender(0-90 ohm)----ground

Or

Battery +ve---ign sw--- Fuel level indicator--- lower tank level sender (0-90 ohm)---upper tank level sender (0-180 ohm)--- ground

Which of the above is correct? Or is neither correct?

I left out any relays or fuses.

Or is it wired some other way?

Thanks,
Doug

 

i can give you the colour coding> low level fuel = brown/pink..........normal fuel level = light green/ orange

 

I have red/white between the two senders (that's also per the diagram) and black (full ground/zero ohms) off the other top tank sender terminal, and green/orange stripe off the second terminal of the lower tank sender. But that doesn't mean it's right. If I found aluminum window screen wrapped around the lower tank fuel pump and a check valve installed backwards on the lower pump (it NEVER would have pumped gas to the top tank), lord knows how it was originally wired. There is plastic split loom wiring cover over all these wires, also, not factory tape..

I am thinking that the green/ orange stripe wire should be on the top tank sender, and the black ground wire on the bottom tank sender.

So, I think it should fuel gauge--green wire---top sender---red/white wire-----bottom sender-----black wire---ground

Doug

 

Should'nt the guage senders and pumps be wired in parallel? IF not (trying to remember my O level physics) won't the pumps' and guages' combined resistances affect their performance?

 

Maybe it help

 

The resistors (senders) must be connected in series and add up (R1+R2=R). So 0..90 Ohm + 0..180 Ohm = 0..270 Ohm on the clock (pointer).

 

That is the contradiction I mentioned, fig 5-4 and 5.5 contradict each other, the wiring is reversed, 5-4 seems to have the ground via the top sender, 5-5 has the ground via the bottom sender.

In any event, with my lower fuel sender I am using, I believe it will be easier to ground thru the bottom sender, its easier to reroute a wire, than modify the new bottom sending unit. Electrically, it won't matter, and nobody will see the wire colors when the car is put back together. Had i had the original Hess sender in the lower tank, it would have been much easier to adapt the new sender guts to the Hess top plate.

Or, maybe I will modify the new bottom sender some more, I will look at it again this weekend. Time involved being the criteria.

Doug

 

I'll measure it over the weekend and report back

 

So, two photos.
Boot tank - the white-red wire is important. This is attached (and also has a matching eyelet) to the lens. The other wire on the flange.



Interior tank - Here, the order of connecting the wires does not matter (tested). It also makes sense, because it doesn't matter which side of the resistor the voltage is applied to, the resistance value is always the same.



After connecting, the clock (if the tank is full) should show "F". If you disconnect the wires from the interior tank, the gauge should settle at about half way.
One more note about accuracy on the clock.
The pointer (lens) in the boot tank is movable (clockwise/counterclockwise). It is only necessary to loosen the fastening a little using the cross screws.
If the pointer does not fit at "F" when the tank is full, you can CAREFULLY turn the nut (perhaps using a suitable driver nut) counterclockwise so that the pointer points to "F".
And of course vice versa.

 

Thats how mine is wired. Wish my lower tank sender looked like that...

I ran a temporary connection wire so i could use the top sender as ground.

I am Leaving the factory wires in place, as I am going to take the time to make one of the two commercial sending unit I ordered, into a pass thru sender so the top sender will once again act as the ground. Probably about 3 hour jib with machining new mount plate and electrical isolation connector/pass thru connections.. The sender can be changed without taking the whole middle part of the car apart, if the wires are left in situ

I put the new tank elbow 45*connector , along with new Tygon lower fuel pump transfer tubing installed into the upper tank.

Now, to make sure it runs, reinstall the upholstery, get the brakes lights working and then get new tires.

 

If you have a bad lower indicator, then it is best (in my opinion) to buy a potentiometer (0-approx. 150 Ohm). Connect to the wires of the lower indicator (it doesn't matter how). Fill the tank and set the potentiometer to "F" on the clock. Then you will always know that if the clock shows half, you still have a full lower tank. And thus gasoline for some distance. Of course, the clock will then always remain at half.

One more note. If you have the H&E Repair manual, please refer to page 294, there is a description of the recall tank problem. Basically, if the top tank is empty, due to the factory design, sometimes the bottom pump is not able to deliver enough gasoline to the gravity tank (via the surge tank in the top tank) and the engine dies.

 

Thanks for the pics!

I determined that i must use the upper tank sender for ground, so i will modify the new lower sender for power in from gauge/power out to top sender. Won't take too long to electrically isolate it, just a strip of nylon to mount the sender potentiometer to and an insulated electrical feed through.

I did ohm my top fuel level sender, with an empty tank, it shows 90 Ohms, not 180 ohms...Don't know if something is keeping the float elevated, or what.

Doug

 

It is 180 Ohms, see original Rochester drawing.