trying to determine ohms for fuel gauge

[fostersds]

I have a 1984 invader and I am trying to replace the fuel gauge. However I am having trouble figuring out which one I need. I know it is 240-33 ohms but I have found one that is 33 ohms E and 240 F and I have also found the opposite, 240 E and 33 F. Which do I need to get? Would anyone be willing to assist a novice? Thanks.

 

[fostersds]

Re: trying to determine ohms for fuel gauge

In cause it is needed, I have a 1984 mercury 115 bp on the boat. Any help or suggestions would be appreciated.

 

[nigels]

Re: trying to determine ohms for fuel gauge

It will depend on the make of guage you have now, your existing one must have worked with your existing sender, (hopefully), email the manufacturer of the existing guage you have and ask them the question, then replace with same.

Or... disconect battery, remove your sender from the tank be sure to disconnect the wires, attach a multimeter (set to ohms) to the positive terminal and ground of the sender, check the ohms at full and at empty positions then you have your answer, buy a guage that is suitable.

 

[BaileysBoat]

Re: trying to determine ohms for fuel gauge

Just ground the gauge. If it reads full low resistance = full.

 

[nigels]

Re: trying to determine ohms for fuel gauge

Not sure if the op's existing guage actually works, but he should try this anyway to see if his guage is broken or not, if broken the guage will read zero so he will be certain about that.

 

[BaileysBoat]

Re: trying to determine ohms for fuel gauge

Not sure if the op's existing guage actually works, but he should try this anyway to see if his guage is broken or not, if broken the guage will read zero so he will be certain about that.

:facepalm: Darn it, you are right, confused "sender" with "gauge"

 

[fostersds]

Re: trying to determine ohms for fuel gauge

Think I figured it out. I tested the sender and got 59 ohms and then tested the connection from sender to gauge and got 59 ohms again. However, when the sender was connected to gauge i only got 23 ohms. i filled the tank up and re-tested and got 30 ohms from the sender. So i figured I would need the 33 F and 240 E gauge. Thanks for your helps folks.

 

[nigels]

Re: trying to determine ohms for fuel gauge

Sounds like you are testing the sender whilst it is still in the tank. (59 ohms is about 87% full 30 ohms is full to the brim are you sure your tank was 87% full? how much fuel did it take to fill it?) Take it out and test it to make sure the sender is good through full to empty, no point going to all this trouble to buy the correct guage only to find your sender is not reading correctly. Test the ohms in the full empty and half positions, half should be +-135 ohms.

Also test your existing guage to see if it is dead or not.

Check with a 12v test lamp or a dc volt meter across the live and ground of the guage with Ignition switch on, lamp should light, volts should be equal to your battery +-, then,

1.Turn Ignition switch off 2. Remove wire from S (Sender) terminal 3. Turn ignition switch to run guage should read zero. Turn Ignition to off. 5. Connect a jumper wire from the ground terminal to the Sender terminal. 6 Switch Ignition on Guage should read full.

If this does not happen then guage needs to be replaced.

Hope this helps. No point buying a guage if its ok and then finding your sender is at fault.