fuel sender

[Frank Hermann]

I have a 1974 31 with 215 gal fuel tank ( diesel) and the gauge stopped working recently.
I believe the sender is bad and would like to know if there is a special sender or can someone recommend a replacement.
Thanks

[CaptPatrick]

Frank,

Isspro is my choice... http://www.isspro.com/page.php?page=ISSPRO_Fuel_Senders" onclick="window.open(this.href);return false;

[Frank Hermann]

thank you for your referral
I will call them and see if they can help
Any suggestions as how to isolate the sender or the gauge?

[Bruce]

Frank,
First make sure you have +12v and a ground to the guage. Turn key on and measure or use a test light.

If you do, take a wire and jump from the ground connector to sender and the guage will go full scale. This is done with the key on making sure not to touch the +12.

If you get full scale that eliminates the guage. If you don't recheck ground and +12, if good and don't go away under load, bad guage.

On the sender should be two wires. The sender connection and a ground.
With key on take the sender wjre off and touch to ground wire. It should go full scale again. If it does, sender bad.

If it doesn't it then could be the following,
2. Bad ground on sender.
3. Bad sender wire to guage.

2 is easy to eliminate by running a temp ground to sender base.
3 can be checked by running a wire temp from sender term on guage down to sender connection on sender.


One can also use this to check oil pressure, water temp, oil temp, gear temp, gear pressure gauges.


Edited to add:
This won't work with microprocessor based gauges or new com systems using single wire data com lines between all the gauges.
It will work with 95% of analog gauges. One of the gauge makers this won't work is AC brand gauges although I don't think I ever saw them used outside a Detroit Diesel application.

[Frank Hermann]

is it necessary to have a ground( makes sense) on the sender?
I dont recall ever seeing one although I may have knocked
it off the last time I was working in the bilge.
Keeping in mind a fiberglass tank this would make sense!
Thanks for the insight and I will loook for a ground

[Bruce]

Yes a ground is needed. The sender is nothing more than a variable resistor to ground.

Sometimes either the factory or in most times owners or mechanics use a bonding wire instead of a ground to engine block.
While they should be connected together at the engine, old electrical systems may have poor connections between electrical ground and bonding system.

Bonding systems should never be used to carry electrical current as a primary capacity. It is for carrying stray currents in the water to a central least noble metal such as a zinc plate to corrode rather than one of the boats thru hulls or such. We tie them all together to make the potential the same between all devices exposed to stray currents.

On dc systems all battery grounds are tied together including a cable between the engines. On rare occasions I've seen where all batteries are isolated from each other and if what powers the gauge clusters in terms of the ground is not the same as the ground on the tank, it won't work because of the isolation.

Trying to cover all angles for you.

[Frank Hermann]

thanks Ill take a look next weekend and check it out.
Maybe this is a saving for me and I don't need to by a sender
Will let you know the outcome