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MG TD TF 1500 - TF fuel sender/dash light

Guys
I am totally frustrated in my attempts to get the low fuel light working properly on my TF. The wiring is quite different than the TD, so I'm asking advise from you TF guys.
Last year it worked properly. I replaced the dash light fixture last year with a good used one. I have it isolated from the metal of the dash plate, as it should be.
I convinced myself that the sender had failed. I went to all the work of replacing the sender with a new one. Before installing it last weekend, I wired it up and had my wife watch the dash light while I moved the float arm back and forth. The light went on and off last weekend!
Now, as before the new sender, the light is on all the time! Tank has about 10 gallons of gas in it.
(fortunately, I have no leaks from the screws or gasket on sender).
I suspect the problem has to do with the black ground wire to the sender. The TF wiring loom includes one.
Should it properly be fastened to one of the 6 screws fixing the sender to tank? I wonder if the sealant I used has blocked my ground.
I don't think I installed it upside down. The positive wire connection is at the top. It always is, right?
Any ideas on why my light is always on?

Tom
'54 TF
Tom Norby

Forgive me for asking Tom, but you did put the sender in with the hot terminal to the top side of the tank? Yes the ground wire should go to any screw on the sender. Your making a complete circuit if the light is on, so it's getting a good ground.
LaVerne

Make sure the terminal wire or fitting is not touching the body of the tank or sender. I think there is a fiber insulating washer that could be left out causing a short? You can do a temporary ground to verify ground not the problem also. If that looks ok, remove the wire from the terminal, and the light should go out. If it does, the problem is in the sender. If not, in the harness or dash. BTW, TD and TF wiring are exactly the same, except for a dedicated ground wire to the TF sender and a different bulb/socket. Both bulbs get current from the A4 fuse terminal/switch, and the sender completes the ground circuit. George
George Butz

Tom - You can quit worrying about the ground - if the light is on all the time, the ground is getting to the sender. Your problem may be that the sender is mounted upside down (as LaVerne asked a bit more delicately than I have stated) or the output terminal may be shorted to ground as George suggests. You could check the first item by looking at how you mounted the sender - electrical output terminal at the top. Removing the wire from the output terminal on the sender will tell you if there is a short to ground within the sender as George suggests. You will get the same light on all the time if the float is stuck in the down position (or is flooded). Cheers - Dave
David DuBois

Thanks
No, I did not install upside down. As I said in my initial post, positive wire connection is on top.
I disconnected that wire, light out. So.....sender is bad or float flooded.
What is interesting is that I had the same problem with the prior unit. That is why I changed it out.
That float was not flooded. So what else could cause light to be on always??

Tom
Tom Norby

I had one where the float was touching the internal baffle. The plastic float had been installed the wrong way around.
If it is the original metal can then bending the arm a little might give sufficient clearance.
darnoc31

Another thought Tom (I know, that's dangerous). I'm getting old and my memory isn't what it....forgot where I was going here. I don't remember if the float drops clear to the wall of the tank. If so the possibility exists that if you had the tank coated the float might be sticking to the wall of the tank. Just a thought ( I know I know).
LaVerne

Laverne, I think that is a good thought. The new one came from the guy on ebay (NOS Locators). It replace one from Moss, and I still have the original Smiths unit. They all have different lengths to the shaft holding the float. The current one was at least one full inch shorter overall, making it less likely that it is hitting the tank wall.
I think I'll jump on the rear bumper and try of move it.
Also, I did as George suggested, using a test wire to ground. No difference.
I guess I'll have to wait until I drive this tank of gas down and pull the darn thing out again. Doing that, I'll be guaranteed to end up with a leaking gasket!!

Frustrated Tom
Tom Norby

Tom, if all else fails, get a mirror and a light and really look at the terminal area before you remove the sender. The original senders have a fine wire that goes through the terminal opening under the insulator, that could get bent up and short (not sure if the new one is like this or not). George
George Butz

Tom--Your situation is very similar, in fact almost exactly, to my situation a few months ago with my TF. I was also installing a new sensor from NOS. What we finally figured was that the new sensor was probably set up for a different car (perhaps Jaguars). I ordered a new sensor from NOS and returned the old one. The new one worked just great. When I installed the new sensor is used a little bit of LocTite on each screw hoping to prevent leaks. Thusfar I have not had any leaks.

Larry
LD Kanaster

Tom, can you remove the 4 screws holding the cover plate onto the sending unit without it leaking gasoline? If so, inside of the box looks like this:
the two parallel brass arms are attached to the float rod and pivot up to touch the fixed brass arm that is connected to ground. The pivot arms are connected to the screw on top of the case by a thin, s-shaped piece of bare wire. If there is fuel in the tank the two parallel arms should not be contacting anything. Bud



Bud Krueger

Larry K
Thanks much for sharing your NOS experience. I will phone them tomorrow. I am convinced that it is the sender.
They seem like such a fragile, simple, under-designed piece.
And Bud, thanks. I have opened my old Smiths, and the just prior Moss sender. They looked like that.
The mystery is: why did the Moss unit I just took out misbehave in just the same way?? Can two different units from two different venders fail in the same way?

Crazy, eh?

Tom
Tom Norby

Your problem, Tom, is that 10 gallons of gas in the tank. At the moment I have the fuel tank of 'the53' sitting on a bench. I've been de-rusting it. I just slipped the sending unit and proved that it's easy to move the float by moving the two parallel arms inside of the switch case. When you drain your tank you can check that way to see if the float is being obstructed before you remove the sending unit. It it's an obstruction issue then I think it's quite feasible for two units from the same manufacturer to show the same problem. Could be that NOS-locators and Moss use the same source. Took me about 2 months of soaking, etc., to get the sender from 'the53' freed up. Bud
Bud Krueger

Guys
Add this to the diagnostic process: last evening I took the old sender, the one I bought from Moss that at one time worked properly, but for the past year was one all the time. I got a test light and ran current through it and it worked just fine: light on and off appropriately. Doesn't that beat all?
And, I disassembled my dash light and placed a new better thin fiber washer between the fixture and the dash panel, to prevent grounding. So that is not the culprit.
When I remove the hot wire from top of sender, light goes out. So, it has to be some internal ground inside the sender.
I use a lead additive with my fuel. I wonder if that allows some short within the sender. A wild guess.

Tom
'54 TF
Tom Norby

Tom,
They worked just fine with fully leaded gas in the 50s.

Regards,

Jim Haskins

1953 TD
J. M. Haskins

Bud, great idea, much easier than removing the whole sender. Could be the angle on the arm- the float hits one of the baffles or something and sticks? George
George Butz

Bud K.
As you have your tank off the car, can you shoot a photo into the sender hole? That way we can see what is in there that the sender arm might get caught on.
Fisheye lens maybe??

And Jim H: D'oh!! I feel dumb. Of course the lead additive wont' make a difference, as the cars were designed for leaded fuel. Just grasping at straws.

Tonight I disconnedted the sender wire in the engine compartment. Disconnected the wire at the connector up front. Light off. So, the problem is NOT in the dash area. Darn, this has me frazzled.

Tom
'54 TF
Tom Norby

Tom, I installed the sender last night. There is nothing in that hole but the view of the inside of the back of the tank. There is a baffle about 4.5" to the right of the C/L of the sender hole. It's virtually in line with the drain plug. I have some images that I took while monitoring the re-rusting. Here's one of the 'almost' straight in view, next will be the toward the baffle. Bud


Bud Krueger

Looking toward the baffle, about 4.5" away:



Bud Krueger

That small chamber is not gas-tight...when you remove that back plate you'll hit gas if it's up that high...and 10 gallons definitely is.
Gene Gillam

Just a caution about NOS-Locators sending units, not related to this Post.

I bought one for my TD. After a year it quit working. I took the sender out and examined it. The problem was that the float was filled with gasoline. Upon further examination I determined that the problem was caused by the end of the wire holding the float wore through the plastic. NOS was kind enough to send me a new float. Before installing the float I bent the end up and away from the float. It has been two years now and no problems.
Frank Grimaldi

Gent
I'm a satisfied man, so some extent. I have solved my diagnostic dilemma.
I finally drove through those 10 gallons of gas. I removed the sender I bought last month. It had gas in the float. So, that is why THAT one did not work. I have not found the leak yet. Must be a pin hole. But, the liquid in it proves the point.
This is the one I bought from NOS liquidators. They said they would send me a new float, so I'll let them.
I looked more closely at the Moss sender I took out last month. Recall that it initially worked, then was on all the time. That float was cracked also. Float failure times two. Those plastic floats are fragile!!

I still had the original Smith's sender with the metal soldered float. That puppy is solid. No leaking there. I decided to use that float and arm on the new sender. Fit right in the hole.
I tested it before install with my wife watching the light. Works!! Who knows at what level the light will come on, but I don't care at this point. I want it to work.
Will install tomorrow. Reading prior posts, you fellows seem to prefer the cork gasket. I have both. I have the cork one soaking in oil now, ready for tomorrow. Which would you use? I have R & R's the sender about 5 times in past 3 years, never a leak around the sender. Don't expect one now. Original tank and screws.

Tom
'54 TF
Tom Norby

I used the cork gasket, soaked in oil for a few hours. No leaks after half day.
All is working well thus far.
Lesson learned....the plastic floats on any replacement sender are fragile.

Tom
'54 TF
Tom Norby

This thread was discussed between 17/06/2012 and 05/07/2012

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