Which ohmn rating gauge do I need?

[RPM 1,190]

Another rookie question. I may embarrass myself so bad with this question I'll have retire from this forum. Auto Meter has about four gauges with different ratings for ohmns:

 

•Empty/Full, 73 Ohms/8-12 Ohms

•Empty/Full, 0 Ohms/90 Ohms

•Empty/Full, 240 Ohms/33 Ohms

•Empty/Full, 0 Ohms/30 Ohms

 

Does it matter which one I use? I've got a 1970 22 gallon sending unit from NPD. Their web site doesn't mention ohmns for the sending unit. My electrical brother is not available to axe. Help Mr. Wizard, I don't want to be an electrician!!!

[j69302 11]

The top one. 10 OHMs full, 73 Ohms empty is the FORD specification.

 

The 22g sending unit should be calibarated for the original gauge. Therefor if you buy a autometer gauge set for the original calibration, it should all end up the same.

 

 

To verify this, drain your gasstank. Get a Multi meter or ohms meter. Stick on lead to the threaded stud where the wire connects to the sending unit at the tank, touch the other lead to the sending unit body, or any bare metal part of the car (ground).

 

Record the OHMS reading, it should be around 73 ohms.

 

Now fill up the tank and check rsistance again. It should be about 10 ohms.

 

Regardless of what OHMs reading you get, buy the gauge that most closely matches your measured ohms reading.

[RPM 1,190]

Cool, thank you very much J!

[SA69mach 39]

You may find some useful info in this post, which is one of my older ones. The gauges and sending units can be frustrating, simply trying to diagnose the problem component is a challenge.

http://1969stang.com/forum/index.php?/topic/52736-make-a-tool-to-test-your-gauges-easy/?hl=%2Bsending+%2Bunit

 

With autometer gauges you should be able to assume the gauge will be accurate and will work out of the box. No issues with printed circuit boards, or 5 volt power feeds, etc. Simple wiring for power, ground and illumination.

 

IF, if you have problems it will be the sending unit or the sending wire. The wire takes power down to the sending unit and the sending unit is grounded to the chassis. The unit provides a resistance (variable with levels/temps)and the gauge shows a value.

 

Ford uses the 10-78 ohm range. That is the range on the sending units on your 69 fastback.

 

Best of luck and don't give up! It took me quite some time to figure it out, and it was worth it.

[RPM 1,190]

Outstanding post SA69mach! Thank you. No idea how I missed your original post or why it didn't come up in my search. Now you guys have me worried about bad new electrical parts. The gauges and fuel sending unit are about the extent of my electrical purchases for my Mach. Thanks again!

[SA69mach 39]

Yes, you are not alone. Being able to test all the parts before installing makes me a lot happier and confident. It also cuts down the time taken to figure out where the real problem lies.

 

My next purchase will be a variable voltage power supply, so I can provide 5 volt power to the gauges when testing them off the car. It is a pain to rig up clips on the CVR when assembled in the instrument cluster.

 

Best of luck to you..

[mustangmike6996 34]

Ford is pretty unique as far as fuel senders go.  As long as you have the corrosponding sending units you can use that guage with no issues.  Easy way to check this is read the resistance for full and empty to get the limits of the sending unit if you cant identify it.

[RPM 1,190]

Thanks guys, you are correct. My tank is new and empty and it read 73 ohms.

[Chelby-Ann 47]

The top one. 10 OHMs full, 73 Ohms empty is the FORD specification.

 

The 22g sending unit should be calibarated for the original gauge. Therefor if you buy a autometer gauge set for the original calibration, it should all end up the same.

 

 

To verify this, drain your gasstank. Get a Multi meter or ohms meter. Stick on lead to the threaded stud where the wire connects to the sending unit at the tank, touch the other lead to the sending unit body, or any bare metal part of the car (ground).

 

Record the OHMS reading, it should be around 73 ohms.

 

Now fill up the tank and check rsistance again. It should be about 10 ohms.

 

Regardless of what OHMs reading you get, buy the gauge that most closely matches your measured ohms reading.

Hey Guys

I am having some trouble with my new fuel gage reading correctly. I have done the following:

1. I have 12V power to the feed terminal at the fuel gage.

2. Checking the gage, I removed the fuel sending wire and with the ignition key on and grounding the sender the gage to EMPTY. Removing the sending unit wire from the chassis ground the gage goes to FULL.

3. The gage and sending unit are acting right.

4. I emptied the fuel tank, Grrrrr,, removed the sending unit and tested it and tests good.

So, I made sure I had good metal to metal contact with the sending unit and the tank and reinstalled the sender and the gage reads about 3/4 full.

I was at my wits end when I decided to search the forum for help and came across this thread.

 

I looked at my Auto Meter Fuel Gage #4314 packaging and see that I am using a 0 ohms empty to 90 ohms full.

I believe I bought the wrong gage and is giving me these issues.

AGAIN OPERATOR ERROR.

I purchased  a 20 Gallon tank with a fuel sending unit brand new from Mustangs Unlimited for a 69 Mustang, so I feel I have that right.

 

Before I spend $50+ on a new fuel gage, to solve my fuel gage problem, would the be the right gage to go with?

Auto Meter Fuel gage #4315 Empty/Full, 73 Ohms/8-12 Ohms.

 

Thanks

Bill

[RPM 1,190]

That's the gauge I'm using Bill.

[SA69mach 39]

The correct gauge for a Ford sender is the 73 ohm - 8/12 ohm.

 

 

chelbyAnn, can you just confirm if your gauge went to empty when grounded? The normal situation is the gauge pegs out to full when grounded, not empty. That is how the stock gauges work.

[Chelby-Ann 47]

The correct gauge for a Ford sender is the 73 ohm - 8/12 ohm.

 

 

chelbyAnn, can you just confirm if your gauge went to empty when grounded? The normal situation is the gauge pegs out to full when grounded, not empty. That is how the stock gauges work.

I removed the sending unit wire and with the ignition key on, I grounded the sending unit wire to a good chassis ground and the gauge immediately went to EMPTY. When I removed the sending unit wire from the chassis the gage went directly to FULL. The gauge is not a stock gauge and the wiring harness is AAW.

[j69302 11]

I removed the sending unit wire and with the ignition key on, I grounded the sending unit wire to a good chassis ground and the gauge immediately went to EMPTY. When I removed the sending unit wire from the chassis the gage went directly to FULL. The gauge is not a stock gauge and the wiring harness is AAW.

 

 

I would check the wiring. Make sure you have the correct polarity at the gauge, and wiring in general. That is behaving the opposite of how it is supposed to behave.

[SA69mach 39]

Can you tell us the gauge you re using, and any technical markings that are on the casing (or paperwork)?  Voltage and resistance range in particular please.

 

Do you have the stock Ford sending unit in your tank?  If YES, then it is fixed at the ohm range of 73-10.

 

I am not familiar with the AAW wiring, but I am going to assume it is set up for the same wiring style as stock Ford. 

 

I am not aware of any gauge that has a default setting of FULL, with no power to the gauge.  Are you sure you don't have the power wire for the illumination hooked up there?  Something not quite right there.....

[Midlife 814]

It's easy for someone to reverse the polarity of fuel and other dash gauge lines, due to the reverse resistance of sending units.  The sending unit line ends up at the grounding point rather than at the voltage source.  Some believe it is the other way around.

[Chelby-Ann 47]

Can you tell us the gauge you re using, and any technical markings that are on the casing (or paperwork)?  Voltage and resistance range in particular please.

 

Do you have the stock Ford sending unit in your tank?  If YES, then it is fixed at the ohm range of 73-10.

 

I am not familiar with the AAW wiring, but I am going to assume it is set up for the same wiring style as stock Ford. 

 

I am not aware of any gauge that has a default setting of FULL, with no power to the gauge.  Are you sure you don't have the power wire for the illumination hooked up there?  Something not quite right there.....

The sending unit is new and is described for a 1969/1970 Mustang from Mustangs Unlimited.

I disconnected the gauge and used a different keyed 12V power source, hooked up a separate ground and tested the gauge again and got the same EMPTY/FULL results.

Here are a few pictures of the Autometer Pro Comp Fuel Gauge #4314 ( we now know its the wrong ohm range) I have now. It appears that from these tests everything is working correctly except for the fuel reading. I ordered a new Fuel Gauge #4315 and its expected to be delivered by April 3.

[SA69mach 39]

The sending unit is new and is described for a 1969/1970 Mustang from Mustangs Unlimited.

I disconnected the gauge and used a different keyed 12V power source, hooked up a separate ground and tested the gauge again and got the same EMPTY/FULL results.

Here are a few pictures of the Autometer Pro Comp Fuel Gauge #4314 ( we now know its the wrong ohm range) I have now. It appears that from these tests everything is working correctly except for the fuel reading. I ordered a new Fuel Gauge #4315 and its expected to be delivered by April 3.

 OK,  I checked the online installation instructions for your gauge, and if you look at the relative values for the gauge you have and the Ford senders, they are completely opposite.

here is reference (which you have in your paperwork)

http://www.autometer.com/media/2650-1079.pdf

 

You have the GM gauge  Empty is 0 ohms, FULL is 90 ohms

Ford gauge and sender    Empty is 73 ohms, FULL is 8 ohms

 

Opposite end of the scales for Full and Empty between the GM and Ford gauges.

 

So, your gauge is reading correctly for its range, it is just the opposite of what you should expect with the correct Ford value gauge.  ie grounding your sending wire momentarily will (should) send the gauge to Full. 

 

You need to send back the 0-90 ohm gauge and get the Ford 73-8 ohm gauge, and all should be well.

[Chelby-Ann 47]

Gas gauge fixed.

Went and filled her up.

Reads FULL now.

Now its off the next problem. Getting the Tach to work.

Thanks for the support TEAM.

Bill.

[SA69mach 39]

Cool.  Glad you got it done.