View Full Version : How best to test a fuel sender off the car?

12-28-2009, 10:10 AM
Have a couple old ones hanging around and want to make sure they are worth hanging on to.


12-28-2009, 10:23 AM
Sorry - should have added that I have a multimeter and when i connect the leads to the using the OHM setting I get a reading of "1" initially and then it goes to nearly zero on the first sending unit. That indicates that I have flow through the gauge and that it will probably work? Yes/no?

12-28-2009, 10:26 AM
That's how I tested mine. Acid test, so to speak will be when I put fuel into the tank.


12-28-2009, 10:28 AM
Thanks Dick. The second gauge remains at "1" (which is infinite, right?) so it's probably hosed.

Can these be easily repaired or it better to pop for a new one?

12-28-2009, 10:52 AM
I thought that as the sender dropped the value should also drop

As - it should not show 1 than a zero. there should be a few decimal numbers in there.

12-28-2009, 11:43 AM
It depends on the gauge and type and type of sender. The ohm range would be 0-90 or 0-180, maybe 0-270. Some have a zero reading at full, some a zero reading at empty.

Do you have the ohm meter set at the correct range??

12-28-2009, 11:44 AM
Hi Don - Happy Holidays to you. I doesn't drop all the way to zero, but it is close.

12-28-2009, 11:57 AM
On a TR2-3B, the resistance should be nearly zero with the float at the bottom. On a TR4-6, resistance should be nearly zero with the float at the top.

Some digital meters do read '1' with the other digits blanked, to indicate out of range. However, the fuel sender on a TR2-3B should never go full open, and I think the same applies to the TR4-6. If it does, the sender is defective and probably will only work through part of the range.

My suggestion would be a new sender; but you've got nothing to lose but time (and sanity) trying to repair the old one. Open it up carefully, find the broken wire, clean the broken ends and twist them together securely. The wire will be Nichrome or similar, which is usually impossible to solder.

If you are really crazy, you can even remove the old winding and try to replace it. You'll need to find resistance wire with the same resistance per foot, and then duplicate the original winding.

12-28-2009, 12:11 PM
Remember all we are testing here is continuity. It should read 0 or infinity on the ohm meter. As you move the float it should be at infinity because you have continuity. Are you connecting the leads to the gas gauge itself or to the connections on the sending unit?
Go to: https://mgaguru.com/mgtech/electric/fg_01.htm for a full discussion on the gauge itself.


12-28-2009, 12:21 PM
Uhm, Dick, "continuity" would be zero ohms, "no continuity" infinite.

But the thread is about how to test the sender, and IMO checking only for continuity is a poor way to do that. Senders "wear out" because the resistance wire rubs through, which both changes the resistance and eventually causes the wire to break.

Note that Barney's excellent article is written for an MGA; the TR2-3B gauge is very similar but not identical. And the TR4-6 gauge (I'm still not sure which one Tom is working on) is totally different.

12-28-2009, 01:47 PM
Your right Randall, been a long time since electricity 101.