1956 gauge voltage

My fuel gauge is reading half with a full tank.

I sent my fuel sender in for rebuild but the rebuilder tells me my sender is working fine.

I asked him about the low voltage regulator ( called constant voltage unit in the gauge circuit drawing in the service manual, page 253, figure49 gauge circuit) and he said I should NOT have a voltage regulator in the gauge circuit in 1956 because Ford used 12 volt gauges in 1956. I assumed he was right because this would explain why my gauge was reading half of what it should be reading (half voltage to the gauge gives half reading). HOWEVER....the pictorial of the gauge circuit in the service bulletin clearly shows what they call a constant voltage unit in series with the 12 volt line to the gsuges....so we have a schematic showing NO low volt regulator and a service buliten that shows one. The wire that goes to the gauges from my fuse box that is connected to a low voltage regulator is too short to make it to the 12 volt buss bar so it looks like the regulator should be there.

I would appreciate comments from anyone who knows what is correct here. Thanks

I just noticed that Service bulletin # 73 was written in 1957. The gauge repair guy told me that Ford went back to 6 volt gauges in 1957 so maybe that is why the service bulletin doesn't show the low voltage regulator. I'm determined to learn the correct setup for our gauges and hope this is helpful to everyone.

I'm at a loss why my fuel gauge is only reading half when the sender is at the full position. The temp gauge seems to be working correctly but my oil pressure gauge is erratic. Sometimes seems right and other times reads very low or doesn't seem to move at all. I've checked grounds and other obvious things. Any ideas out there? Can some 1956 Mark II owners please look inside your fuse box and tell me if you have a low voltage regulator mounted to the vertical end piece of your fuse box/ It is a small rectangular unit with 2 connections. 12 Volts and the low voltage out. The case is ground. This is on the outside of the fuse box towards the rider side fender.

Jack,

The entirety of Service Bulletin #73 (including the fuel level measuring system drawing) is for a 1957 Lincoln, it is not for a 1956 or 1957 Continental. As mentioned in another post the service bulletins jump around from Lincoln to Continental so one needs to be careful about which they are referring to.


1957 Lincolns had a constant voltage (ie. swing rheostat) type sender and so were fitted with a) a constant voltage unit (ie. a voltage stabiliser as someone has added to you car), and b) a SIP Relay to operate the low level light. This is clearly described in the 1957 Lincoln service manual which I happen to have a copy of.

The 1957 Lincoln constant voltage unit is 12v so probbaly puts out a constant 10v.

No '56/57 Continental should have a constant voltage unit because they don't use a resistive sender unit.

Bypass the constant voltage unit and see what happens re the fuel gauge, unfortunately unless its faulty I don't think that'll be the problem.

If it still bad, and since you've already had the sender checked and the earth's are OK, then it points to the gauge unit itself. If the bimetallic strip in the gauge is suffering age related hardening then that would explain the low reading when the average current is correct.


Hope this helps,

Mark, I just noticed this post and am confused about paragraph 4.

Did you mean to say it should NOT have a constant voltage unit?

OOPs, I just noticed you have the word NO in front of this. I need to read more carefully.

Jack

Hi Jack,

The Continental MKii has a fully bimetallic gauge & sender system and because this is inherently self compensating for variations in supply voltage it does not need and constant voltage unit to function properly and accurately. You can fit one but you don't need one. adding one won't make the system work any better or worse.

Conversely many cars (including the 1957 Lincolns) have a mixed system of bimetallic gauge and variable resistance sender (basically a potentiometer). This type of system is sensitive to variations in supply voltage leading to errors in the gauge reading so a constant voltage unit in the supply is indeed mandatory.

The most common variation in supply voltages are a) ignition one but engine not running so 12VDC, b) engine running at moderate to high revs supply voltage (from the battery charging voltage regulator at the side of the radiator) is then approx 13.5VDC, and c) engine running at low revs so charging regulator kicks-out so again supply volatge is 12VDC.

The above variations impact the gauge reading for a mixed fuel level system but not for a fully bimetallic system. Indeed in the MKii fuse box you can connect the black supply wire directly to the yellow sender wire and the fuel level system will work perfectly ...but just don't do it for too long unless you fit a step down resistor inbetween (33 ohm 2W resistor is recommended).

Thanks Mark, I understand all that but my gauge won't read full with the resistor in series.

Maybe my bi metal is tired/stiff and needs more current than yours. I suppose they can get stiff after a half century. I know I am more stiff than I used to be. Ha

I don't want to burn out the gauge however so I'm not sure what I should do.

maybe I will put a smaller resistor in series with my 10 Volt output on my new regulator. I'll try 22 ohms.