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Timer
07-03-2001, 06:43 PM
As I'm a dunce on electrical, I know I need help on this one.
I have a fuel gage for each tank. (It's a dual feed system.) One gage won't work so I went to that tank and grounded out the tank terminal which made the gage needle jump to the top of the gage. So I figured the gage was OK.
I then went to the gage which has 3 connector terminals. Two of the connectors have 2 wires going to each of them. The third has one wire to it. I pulled the one wire off of the third terminal and touched a ground to it and the needle jumped to the top of the gage. I did the same to the good gage and the same thing happened.
I figure the problem is somewhere between the ignition switch and the gage, but I'm lost as to how to progress. What do I do next to isolate/correct the problem?
I can always operate with one gage but that's not in my nature. Thanks for any help anyone can give on this.
P.S. All of the tests were done with the ignition switch on.

Havasu Hangin'
07-03-2001, 07:08 PM
Could be a bad sending unit.
On each gauge, you should have 3 wires- IGN+, GRND-, and sending unit. I assume it's the sending unit wire you took off & grounded. The IGN+ and GROUND- wires usually have more than one wire, as they are run in parallel with the other gauges (all together).
When the key is on, the IGN+ should have power- check it with a dummy light (no offence). If it works, ground the dummy light to GROUND- if it works, your gauges are getting power and ground.
The first thing I would try would be to swap the sending wires on the gauges- if the problem switches sides, then it's the sending unit- if not, it's the gauge.
A sending unit in your tank is nothing more than a resistor and a float. As it floats higher, more resistance, the gauge reads full. Hence, when you grounded that wire fully, the gauge read full. Sending unit tend to fail because of the environment they're in- eventually they rust & die. I've replaced a couple in my time.
They make universal sending unit kits- you can get them at West Marine, etc. Check to see your bolt pattern, and go get a kit that fits. Read the instructions, as you have to adjust it for the depth of your tank. No lie- it's a 10-minute job.
Hope I didn't confuse you too much!
http://free.***boat.net/ubb/biggrin.gif

Timer
07-03-2001, 08:59 PM
Thanks HH. Sounds like you know your stuff -- very clear directions.

Timer
07-08-2001, 03:51 PM
HH, I switched the sending unit wires on the back of the fuel gages and the other gage registered a reading. I then unhooked the wires from the bad sending unit (at the tank), removed it to get the name, etc. off of it and took it apart out of curiousity. Nothing was obviously wrong with the insides per my uneducated eye so I put it back together and hooked the wires back up to it without putting it back in the tank. I then moved the float up and down and no matter where it was positioned the fuel gage was pegged to the max. It seems like the gage shouldn't have even registered, as it didn't register before I removed it. Can you figure that one?
Anyway, it's a Medallion Instruments sending unit so I'll see if I can get something that matches it.

Havasu Hangin'
07-08-2001, 05:14 PM
Originally posted by Timer:
Can you figure that one?
Well, very interesting. One question- did you ground the sending unit to the tank while playing with it? I believe it should be grounded to the tank (by the screws or a wire) for the resistor. Perhaps that's why it was acting funny.
If the sending unit is bad, there won't normally be an visable signs. My last one looked great, but worked when IT wanted to.
Originally posted by Timer:
Anyway, it's a Medallion Instruments sending unit so I'll see if I can get something that matches it.
I have Medallian as well. Good luck finding parts, as I understand they got out of the consumer business. In fact, when I replaced my oil pressure sender, I got one of the last in the warehouse. I was told that the oil pressure sender was a unique scale- I hope it doesn't go bad.
Luckily, there are universal fuel sender kits that work with the same scale as Medallion. There are a couple sizes, depending on the depth of the tank. If you don't feel comfortable yet that it's the sender, you could switch senders, but I think you're on the right track. I think the kits are around $20-$30 (the cheapest part I've replaced to date!).
Let me know how it comes out!
[This message has been edited by Havasu Hangin' (edited July 08, 2001).]

Timer
07-08-2001, 05:52 PM
When I did the last test, the sending unit was not grounded to the tank directly. Hmmm, hope that explains it. I'm intent on replacing it anyway, as the switching of wires at the 2 gages as you suggested makes sense as a test. Thanks for the help -- I'll let you know how it turns out.

Timer
07-12-2001, 10:18 AM
HH, I just finished putting in the new fuel sending unit and the problem is solved! Thanks for the help!!
I ran into a problem with the bolt hole pattern of the new sending unit. It measured OK in the parts dept but when I actually tried to install it, the holes were off just enough so I couldn't put in the screws. I then carefully measured the distance across alternating holes and found a slight dicrepancy. Thanks Stewart Warner!!! After a lot of hole drilling to enlarge them it finally fit. What a pain!

Havasu Hangin'
07-12-2001, 04:38 PM
Originally posted by Timer:
HH, I just finished putting in the new fuel sending unit and the problem is solved! Thanks for the help!!
Hey, I knew you could do it! Glad I could help. Now you can add "boat mechanic" to your resume.
As far as the fabricating, I hear ya. It seems like I'm fabricating something on a weekly basis for my old boat. http://www.goldenplasma.f2s.com/forum/smilies/happy34.gif
[This message has been edited by Havasu Hangin' (edited July 12, 2001).]

froggystyle
07-12-2001, 05:19 PM
HH, I'm not suprised it was a bad sending unit, but I believe you are mistaken on the wiring. There is rarely a hot lead going to a tank, unless it has a fuel pump in it. They usually (every one I've seen) work on a resistance principle. You probably purchased a 90-270 ohm sending unit or something the likes? It works by measuring the resistance between the gauge and the ground. What it is important to get right, is that the gauge and the unit have a similar, good ground. There is usually one sending unit wire (to gauge) and one going to an engine ground, as the boat is fiberglass, and grounding to the mounting screw will not work.
I have been known to be full of crap in the past though http://free.***boat.net/ubb/wink.gif

Havasu Hangin'
07-12-2001, 05:36 PM
Originally posted by froggystyle:
...but I believe you are mistaken on the wiring. There is rarely a hot lead going to a tank, unless it has a fuel pump in it...
Hey Froggy. In my original post, the hot wire test was for the gauges- to make sure they have power & ground.
Originally posted by Havasu Hangin':
On each gauge, you should have 3 wires- IGN+, GRND-, and sending unit. I assume it's the sending unit wire you took off & grounded. The IGN+ and GROUND- wires usually have more than one wire, ...When the key is on, the IGN+ should have power- check it with a dummy light (no offence). If it works, ground the dummy light to GROUND- if it works, your gauges are getting power and ground.
Maybe it wasn't clear. Next, I said to switch the sending unit wires on the gauges. You are correct- the sending unit works off ground (resistance) only.
Originally posted by froggystyle:
I have been known to be full of crap in the past though
I can't believe that...I bet there isn't even any erasures in your house... http://www.goldenplasma.f2s.com/forum/smilies/happy02.gif

froggystyle
07-12-2001, 09:00 PM
That's called an IDIOT light! Jeez, tough to get a break in here. You're right. I mis-read your post and missed the gauge part. I was focused on the sender already. http://www.goldenplasma.f2s.com/forum/smilies/confused24.gif
You da man!