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Joseph Book
Joseph Book, Classic Car Mechanic
Category: Classic Car
Satisfied Customers: 61
Experience:  Diesel Technician and classic car builder
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Installed new sending unit in gas tank,it only has one post.

Customer Question

installed new sending unit in gas tank,it only has one post. ran single wire to new gauge that has4 post on it 1 is for light power 1 is for light neg 1 is for 12vt switch and the last one is marked "S" for sending unit going to the tank. when I turn on the ing key the gauge needle goes from below "E" to "E" . but when I use a test light to test at the "S" terminal or the post on the unit at the tank the needle swings to 1/4 tang where it should be. why is that? like it has to have a load or draw to work
Submitted: 1 year ago.
Category: Classic Car
Expert:  Pete replied 1 year ago.

My name is ***** ***** I am a professional here at Just Answer. I noticed that your question had not received a response and thought I would see if you still need help with this.I apologize for the delay and I hope I can still assist you with this here.

Usually the sending unit needs a ground to operate.Make sure you have a ground connected where it should be and see if this corrects this fault here.If this is or has been attempted with no success let me know.

If more help is needed, use the reply tab to continue our conversation. If no further assistance is needed, kindly rate my service.You can rate at any time and we can continue to work on your question as this will not close out your question.Keep in mind in some cases it can be difficult to fully diagnose or help repair your vehicle without seeing it and I work on delivering the best possible answer from what I see to work with.

Thanks Pete

Customer: replied 1 year ago.
Thank you Pete I probably should have put that in my comment write a ground at the rear of the car also ran a separate all the way up to the battery still no difference seems like when you put a draw on it with a test light it moves right to where it should be any more suggestions please let me know thank you
Expert:  Pete replied 1 year ago.

Was the sender that was installed one that is made or compatible for this model here?

Customer: replied 1 year ago.
it was the tank and sending unit is for a 49 Mercury everything fits perfect and the gauges are made by vintage gauges
Expert:  Pete replied 1 year ago.

Unfortunately this is all of the info I have on this here myself.

I will open your question up for others here to see if someone else can assist further on this as there may be others here that may have more info on what to check or do with this issue.I hope you can get this resolved with ease.No need to reply to my last post here unless it is a last resort as it will keep your question locked to me and others will not be able to view it.If you feel you want to continue to work with me on this feel free to reply at any time but keep in mind in some cases it can be difficult to fully diagnose or help repair this without seeing your vehicle.

Thanks Pete

Expert:  Joseph Book replied 1 year ago.

Good Afternoon Pete, I am Joe one of the experts here at Just Answer. I have a few questions that will help me route you to the right answer. The fuel sending unit that you installed is a direct replacement for a 49 Merc, correct? Your gauges are aftermarket gauges from Vintage Gauges or are they 49 Merc Replicas?

Customer: replied 1 year ago.
The gas tank and sending unit was ordered for a 49 Mercury replacement the gauges are vintage gauges not replacement. I still don't understand after running aground at the back of the car and then one up to the battery that when I use the test light and it puts a draw on the sending wire it barely lights up the test light what is enough to move the gauge to a quarter tank where it is proper. I have yet to find in any forum how much is voltage should be going back to the sensor maybe that's part of my problem
Expert:  Joseph Book replied 1 year ago.

the sending units are variable resistors with a specific ohms range and the fuel gauge needs to match that range.