Fuel Gauge pegs, not sure where to start

[FillupD]

I have a 1989 Tracker 1800 sf and the fuel gauge pegs when I jump the sender wire to ground on the sending unit.That (from reading lots of posts) tells me the sending unit is bad? I am getting 134 ohms reading out of it though. At my fuel gauge I am getting the same but it is below E, not responding at all. When I turn on the key, the ohm reading goes to 1 or disappears. I have 12 volts going to the hot wire. I think I have a ground problem but I don't know where to start?

It did work before a bunch of mods.
I removed the old 12/24 volt trolling motor and plug and replaced it with a 36 volt plug. Power is coming from a min kota breaker by the batteries and the ground is going to a grounding post. The old 12/24 switch was also removed. That grounding post also goes to the starting battery neg, (because I read that is what to do).
This was an added thing but the post is bolted to the boat frame but its back is plastic so I don't think that is the problem because it is not really grounding the boat, just the trolling neg battery cable. I have the 3 batteries connected for 36v and it checks OK.

I reworked some wires on the trim pump motor but didn't add or change anything there. I really can't see where any wires back there are hanging loose where a ground should be connected.

So I have an ohm reading at sender and gauge with key off
I have no reading at gauge with key on, sorry I guess I didn't check a reading at the sender with the key on.
When I jump pink to ground on sender, gauge pegs.

Any advice out there on where to start tracking this down? I have read a bunch and I can't find anything as screwed up as this seems.

Here is one thing I noticed. There is a flasher in it and it is noisy. After I removed the control and turned the cables around so it would go forward when pushed forward, ( I just got this boat and started cleaning the special rigging up)
The flasher quit working and it was quiet when I turned on the main power. Then one day, I turned on the power and it came back to life. I don't know if the fuel gauge worked at this time or not.

 

[mjf55]

Fuel gauge will read full when the sender to ground resistance is 33 ohms ( or less), and will read empty at 230 ohms. You say that when you put the S terminal to ground it pegs ( full? ) the gauge. Also, you have a resistance of ~134 ohms at the sender ( terminal to ground) and also at the wires at the gauge ( I assume With the pink ( sender) wire off the gauge.

Make sure you have 12 volts at the I terminal when you turn the key on ( use battery ground, not the ground at the gauge )
Make sure that you have ground on the G terminal of the gauge. ( check for 0 ohms between the ground on the gauge ( ground wire ) and say battery ground )
Now, with all wires connected on the gauge ( I, G and S ) and wires on the sender ( terminal and ground ) and the key on, the gauge should read over 1/2 full.

If not, I suspect the gauge.

Make sure all connections are clean and good.

 

[FillupD]

Thanks, I used the ground that was on a fuse box and not on the gauge, I didn't check the gauge ground G terminal resistance but I will now thanks to your suggestion. I have 12v on the gauge but I'm not sure if there is 12v off and on. I do know that when I turn the key on, the ohms drop to 1 or blank from 134. I do have about a 1/2 tank in there.
I'll check G terminal between that wire and ground on fuse block. Make sure it reads 0 ohm.
I'll see if I have 12v when key is on, I'm pretty sure I do. When 12 v hits, the ohm reading goes off.

Thanks, I'll check it tomorrow. I almost get stuck under there it is so tight. I have to kind of wiggle under there and it makes me nervous I'll get stuck under there and can't wiggle back out.

 

[FillupD]

My pink wire was not off (removed) from the gauge when I checked the resistance. I got the reading from the S gauge post with it all hooked up.

 

[mjf55]

If the sense wire is connected when you measured the resistance, then i am not sure of what the total system ( gauge + sender ) would be. That is not specified ( as far as i know ).
Also, you cannot measure resistance when power is applied because the DVM itself sends out a small current and measures the voltage drop. It then knows the resistance using Ohm's Law. By adding 12 volts to the mix, the meater cannot read the drop correctly.
So, you have 12 volts on the i terminal when the key is on, you have a good ground at the gauge, and you have a known 1/2 tank of gas with the correct resistance ~130 ohms at the guage end of the pink ( sense) wire measuring feom pink wire to gauge ground.

You have all the correct inputs to the gauge, but it reads incorrectly. I still highly suspect the guage.

 

[FillupD]

I'll see if I can come with another gauge to test it out. My scenario is I have a reading (ohm on pink) at gauge but when 12v are applied, the reading is gone. The gauge never does move, except if I jump the pink with ground at the sender.
I'll get that ground at the gauge checked today and see where I'm at before I buy a gauge though. I'll try to keep it at one step at a time.
I am using a VOM for testing.

 

[gm280]

My 2 cents worth. If your fuel gauge and sensor worked before you did any new wiring, then they will work after you figure out what your new wiring stirred up. I'm thinking grounds and battery voltage issues on this one. Not the fuel gauge or the sensor. JMHO

 

[FillupD]

I couldn't get the ground wire all the off the gauge without pulling the steering wheel, windshield and dash board but I did get a 0 ohm from the center of it to a ground. I have 12 v when key is on. I unhooked the ground from the back and re-did all the grounds back there on a block strip instead of 5-6 eyelets on one screw. At least I have my pumps and aerator wires figured out now. When I check ohm with the wire disconnected from ground, but not disconnected from the sending unit, I get 4.3 ohm. Should this one be 0 also?

I guess I need to plan on looking up on how to remove the dash and give it a good going over. My pressure gauge is pegged and I want to fix that and find where it all hooks up too. Looks like a tube running back there and it squirts out water when it is running.

 

[FillupD]

After I redid about every ground in the boat, which probably needed all sorted out anyway, I took my sender apart, cleaned and polished the connections and inside surfaces where magnet makes contact. It was pretty dirty under the glass looking bulb where the pink wire hooks onto. Turned out to be a bad ground on that sender, works now. Thanks everyone for the help and suggestions.