Fuel sending unit location?

[chester40391]

Hi, new here and new boat owner. I have an 83 Ebbtide Catalina 18ft10 I think.
I haven't found yet how much fuel my tank holds. I have 2 gauges that dont work properly, Trim and Fuel. Trim always shows up as soon as ignition is on but right now im mainly interested in the Fuel gauge. In case it matters engine is 302 Mercruiser Alpha 1

I am very familiar with testing the sender and gauge. Upon inspection the fuel gauge was disconnected from all wires. After some research and wiring diagrams found here I found I dont actually have a sending lead there to attach. There is a loose wire but its not the color I expected (some shade of orange) but either way if that the one then im getting no ground signal from it.
I would like to trace the wire back from the sending unit and if needed test the sending unit/connections directly.

My problem is that I have no previous knowledge of where a boat sending unit would be and I have been unable to determine this from online search. Yes, I do know its on the tank! But where are the tanks normally? is it on the back of my tank near the engine or closer to the bow? Im guessing that since I have put in at least 25gal of fuel at one time that this would be a single tank behind the under storage compartment closer to the engine, or would there be more than 1 tank thus going up both sides instead of the middle? Im also guessing since I cant find this info online that it should be obvious but I think it has been covered up by replacement decking.

It might also help to know the path the original wiring would have taken from the sending unit to the gauge. I do have 2 unknown/disconnected wires that come up along with the fill hoses near the fill hole. One of these is black and the other is an off orange color similar but not the same color as the extra wire I spoke of near the gauge. I read no ground signal from either of these wires and no resistance across them..

Thanks for your time. Sorry it is long

-Chad

 

[Silvertip]

Re: Fuel sending unit location?

To determine the location of the fuel tank, follow the fill hose. If the fill hose is at the back of the boat (which it usually is) the tank will also be in back. The sender is installed in the top of the tank but if it has been covered over with new decking, you need to find someone with an identical boat with hopefully an access port over the sender. You can then measure where it is, transfer those measurements to your boat and cut the access hole.

The color of the fuel sender wire at the sender and its color at the gauge should be the same. Your ohm meter can tell you that. It doesn't matter what route the wire takes to get there. Some shade of orange (faded perhaps) could be pink. You have a 27 year old boat and who knows what has happened with the wiring over those 27 years.

The shell of the sender must be grounded, the filler is grounded and the center threaded post on the sender goes to the "S" terminal on the gauge. If +12 volts and ground are present on the gauge, the system should work. +12 volts and ground can be obtained from the same terminals on any other gauge (that works).

 

[chester40391]

Re: Fuel sending unit location?

Thanks for the prompt reply.

The filler is around the bow but the hose travels toward the back on the passenger side (sorry I don't yet know the marine terminology) But I cant see very far without removing some decking. So I would say its in the back in front of the engine.

Yeah when I got it the filler was not grounded. I quickly remedied that.

As far as the color of the wire is that I have no control to measure against. i dont know if either wire is the sending wire that im looking for. For this same reason knowing the normal path of the sending wires could prove helpful. Is it normal to have the sending wire come up with the fill hose or does it normally come from the back of the boat with the other wiring?

Id rather not do the work of removing my carpet and decking to then find that its simply the sending wire got pulled back away from the instrument panel out of sight and not either of the 2 lose wires I was looking at.

-Chad