Fuel gauge help!!!

SO this is a weird one.
I have a 2012 tacoma and got my fuel pump changed by a friend of mine.

The issue is this.
My gauge reads empty, I know you are all going to say SENDER SENDER but hear me out.

Things we have done.

We pulled the pump back out and checked the sender, measured the resistance during full sweep, it all checks out.

We plugged the sender into the truck and lifted the float, it sweeps on the gauge from Empty to full like it should.

So wheres the problem you might ask... this is where it gets weird.

If i turn the key on with the float at E and sweep it to full, it works 100%
If i turn the key on while the float is at 1/2, the gauge jumps to 1/2 Works 100%
If i turn the key on while float is at 3/4 Gauge shows 3/4 instantly - works 100%
If i put the sender to FULL while the key is OFF, the gauge will ALWAYS read the last spot it was on, so say i turn the key off while the gauge is at 1/2 and i put the sender on full and turn the key back on, its still at half. Anything after 3/4 full does it, the HIGHEST it will go to while turning the key ON is 3/4.
Yet if have it anywhere below 3/4 and turn it on, the gauge corresponds as it should, if i lift the float to full the gauge goes to full.

It only does not work if the float is already at full when turning the key on.

For example to make it read right, we plugged my sender in turned the key on, then stuck the pump in the tank. Its going down as it should as i drive and run my tank down, when i refill, it gets stuck at w/e it was when i fill it full


Sorry for this long post, i hope i explained my issue well enough. This is frustrating me and i cannot figure this out.

Any thoughts?

 

The ground is controlled through the Instrument cluster. So would i not have issues with all the circuits in that line?

 

Did you check the resistance with a digital or analog(needle) meter? If there's a bad spot it may not show on a digital meter. Did the problem just start after the fuel pump change? My guess is.....a bad sending unit.... I suspect it has a bad spot on the potentiometer of the sender, an analog meter should show this. Is it possible the sender was damaged or bent during the fp change?

 

We used a dvom when we tested it, i thought of the analog thing but, why would it sweep properly on the dash as well? Its only when i turn the key off, put it to full and turn it back on it doesnt work.
The problems did start after we did the pump. I don't see how we could have damaged it, but you never know.

I had that flow chart haha.
Only thing i did not try is shorting the wires together while the key was off, then turning the key on to see if it goes to full.

My resistances are all in spec.

 

Sender.....Sender......Sender.....

 

Haha I guess I will try find one. And get Bck to you

 

As of today, I have NOT ever had to dig into a fuel gauge issue on a Tacoma, so I have nothing to bring to the table from a hands on Tacoma point of view.

HOWEVER....For years and years, up until 2 years ago, I had a business where I restored antique tractors. They are almost famous for electrical issues (because of sitting outside in the elements most of their days) From the late '40's on, MOST tractors had fuel gauges. Some were simple float types, but mant were electrical gauges (such as modern automotive types) .....I had MORE than my fair share of experience with fuel gauges that didn't work/didn't work correctly/worked intermittently. THAT said, somewhere in the neighborhood of 90%/95% of the electric fuel gauge issues I've ever dealt with WERE BAD GROUND RELATED in nature.

JMHO, and worth everything you paid to get it.