Cortina MK1 fuel sender.

[peteleo]

A reading of 20 ohms at the fuel sender should read full on the gauge.
What does the gauge read when you touch the sender wire to ground ?
or what voltage reading do you have at the fuel gauge ?

[1970 cortina GT]

Hi Pete, so I have 3 volts at the sender, 1.8 volts at the gauge. My son is currently at school and has done a chart, you probably understand it better than me but I’m not sure from the figures what the issue is. Thanks for looking at it.

[peteleo]

MK1 GT '66 voltage stab. output should be a pulsating volts 5 volts
( square wave 0 volts to 5 volts )

First check the 12v input to the volt. stab. output 0-5v. Output wire connects to #1 terminal to the f/gauge. #2 terminal of the fuel gauge goes directly to the sender.

Somehow you are getting a high voltage drop at the sender ??

Your son's ohms law calculations works though.

[1970 cortina GT]

Ok I’ll check when I’m back home on the weekend, voltage stabilizer is new so I’ll check my connections. Thanks Pete I’ll let you know what I find.

[1970 cortina GT]

So I get 12 volts to the voltage stabilizer. I get 5 volts out of the voltage stabilizer. I have the sender out and it reads 20 full and 200 empty when I move it manually. I have hooked up my MK2 fuel gauge using the MK1 wiring harness and that reads half full when I manually move the sender arm to simulate a full tank. I know the MK2 gauge works fine. This is baffling me as it is a pretty simple circuit but I can’t figure out what to try next.

[peteleo]

Just to clarify. Your using a MK1 GT voltage stabilizer with a MK1 C5BH sender unit to a MK2 GT f/gauge. I think you may need a MK1 GT f/gauge, will solve the problem.

[1970 cortina GT]

Hi Pete, I’m using a MK1 fuel gauge, a new MK1 voltage stabilizer and a new MK1 20 ohm full, 200 ohm empty fuel sender. I get a reading on the gauge of half tank when it’s actually full, despite a reading of 20 ohms. I get the same, half tank reading when it’s actually full when I try hooking up my MK2 fuel gauge which works fine on my MK2.

[peteleo]

Sounds like you have some additional resistance in the harness or the wire is not going directly between the f/gauge and sender unit. Take a single separate wire from the f/gauge to the sender.

[1970 cortina GT]

I’ll give that a try and let you know, appreciate your advice.

[Brett Wilkie]

This may sound silly and unlikely but is it possible that the tank itself is somehow not grounded fully to the body?

[peteleo]

I believe Lee also grd'd the tank which made no difference.

[1970 cortina GT]

Yes I ran a separate ground from the tank to the battery to be certain. The sender seems to read accurately, the gauge seems to work correctly, the voltage stabilizer seems to work correctly . There really isn’t much else to it but it still isn’t giving an accurate reading . I have the sender out, the gauge out, a gauge out of my MK2 out. Jeez I’m missing something simple here. I tried the sender at the gauge with a short piece of wire and even when I simulate a full tank on the sender it still only reads half a tank on the gauge.

[peteleo]

You haven't mentioned, that the voltage stab has to be grd'd.

It could also be the the pulsating square wave duration is not right. Staying too long on 0 volts and short on 5v. Try a used v/s.

[1970 cortina GT]

Yes I made sure it’s grounded, in fact I added an extra ground to the whole speedo as the ground from the bulb connection didn’t seem too great. I don’t have a spare voltage stabilizer but surely the other gauges would be inacurate if it was faulty. I think I’ll try and run a wire straight from the voltage stabilizer to the gauge, just in case there’s something going on in that part of the loom.

[Brett Wilkie]

Does it make a difference if you reveres the polarity of the stabilizer? If you get totally messed up I MIGHT have a Mk1 fuel gauge and stabilizer here if I didn't discard them yet?