Pontoon Boat & Deck Boat Forum

The fuel gauge on my 2013 Sylvan is constantly reading max full.
When I disconnected the sender unit at the tank, the gauge dropped to empty so I assumed the sender unit had a short in it and purchased a new one.
The new sender was installed yesterday and the problem is the same as before...... Grrrr!

After further investigation, the sender is working OK - ohm reading changes as the float is raised and lowered.
From what I can make out, the gauge has 4 wires going to it - 2 for the illumination lamp (+12v and -ve) and 2 for the gauge reading (+12v and the sender signal cable).
The sender signal cable reads 6.5v with everything connected correctly (as the sender unit resistance is causing this volt drop) and 12v if I disconnect the ground side of the sender unit. This is as I'd expect - but the gauge stays showing full all the time.

Am I missing something or is it just a duff gauge?

And it has a nice plug on the back of it for easy disconnecting but this may be a pain to get a replacement. There are no manufacturer names on it and the only numbers are 781491PMFB and 326/12 - neither of which show up in Google.

Any help greatly appreciated.

Sounds like your on the right track. I haven't had to look at my boats gauge but I have worked on some vehicle ones. Sounds like you either have a bad gauge or a open on the sending wire. If you can test at the pigtail on the gauge and you have +12V and a varying resistance value when you move your sending unit float I would bet on a bad gauge, or maybe bad connection at the pigtail. Generally if you get stuck on full or empty you have either lost your positive voltage or are shorted to ground on the sender side or have a bad gauge. It's a pretty simple circuit to test. If you can't get an exact replacement anything aftermarket should be pretty straight forward to install. Good luck!

I used to have a 5/16" dowel I stuck down into the tank to check my gas level. It was 100% accurate.

A lot of problems with gauges and the dash boards are grounding problems.

Bamaman wrote:I used to have a 5/16" dowel I stuck down into the tank to check my gas level. It was 100% accurate.

Yep, just light the end of the dowel, stick into the tank, to illuminate the fuel level, right??

Yep it was the gauge. I've got hold of a second hand one which has the same plug on the back (4 pin packard connector) and it's working OK.
But it has a black dial whereas all my other gauges are white faced.
When people have ordered gauges, is it easy to specify the type of connector on the back? I've had a quick look but can't seen anything.