Peterbuilt

No, that should not matter.

Any chance the 12 volt and the ohm wires are backwards at the gauge?

MBrianB

I'm installing a new M&H harness. The connector is indexed by the bumps. I suppose the wires could have been installed backwards. I will check to see of the hot wire is actually the bottom connector.

I also thought to put power to the lower connector and ground the ground post and see if it gets hot without going to the sender.

Peterbuilt

OK. Let's try that, just be ready to kill the power or disconnect the battery.

MBrianB

Checked the connector and the hot wire is the bottom one.
Put power to the bottom tab and connected the ground and, nothing.
Checked the sender wire and it goes to ground???
I don't think that is supposed to happen or is that how the tank sender works?

Peterbuilt

The ohms wire goes from the gauge to the sending unit in the tank.
A variable resistor changes as the float goes up or down and its all connected to a ground.

MBrianB

Then it must be a problem with the sender in the tank.

Or I just use a yardstick!

0Willcox Corvette

I'm sorry, I've been on vacation killing lobsters in Maine... lol..

So.. lets to a fundamental test

With the key on, pull the ohms wire off the sender.... When you do this the gauge should go to full.... Next take the ohms wire from the sender and ground it out... the gauge should go to empty.

If this works as pictured below, the issue is most likely in the sender... if the gauge doesn't function this way the issue is the gauge. The picture below should help you figure out the issue.

Willcox

MBrianB

MBrianB

Did the test procedure above. Gauge checks out fine per the results. It must be the sender then.

Still doesn't explain why ground post on gauge gets hot???

Peterbuilt

The gauge tested good so how about installing the gauge in the canister and with a fused jumper apply 12 volts to the bottom terminal and see what happens.

MBrianB

All tests were done while the gauge was in the cluster and grounded to the cluster. Ground was supplied by the temp gauge. The temp gauge and the fuel gauge were the only gauges/lights in the cluster that were connected.

0Willcox Corvette

Well my next advice would be to pull the ohms wire off the sender and take an ohms reading off the stud.

A follow up test would be if you have an old turn signal flasher laying around you can run one wire from the flasher to ground and the other to the sender wire.

Normally a flasher will have around 50 ohms on it (you can check this before you do this test to know exactly what ohms the flasher is reading) then when installed this flasher to the sender wire you should have just above 1/2 a tank showing on the gauge. This will let you know for sure the issue is the sender and not the gauge.

Willcox

MBrianB

I was doing that exact thing when you posted
There is 1.2 Ohms resistance which is probably caused by using probes. It is really 0 resistance, essentially grounded out.
Too bad since it is a new sender.

0Willcox Corvette

Nope.. 0 would mean it's putting out 0 ohms... 1 on a multimeter is open circuit. It's a 72 so get something like a coat hanger, and go in the tank and move the lever, see if the reading changes.

MBrianB

OK will try that.
The ohms connector on the gauge goes to ground? Is this correct?

MBrianB

Coat hanger moves the float up and down and the reading on the gauge corresponds to the float level.
Gauge connections stay cool.

Release the float to empty and the gauge connections (pink +) (Ground -) get real hot real fast.

Peterbuilt

That's interesting!
Time to remove the sending unit and find out why it does that.

0Willcox Corvette

The sender must be shorting out to cause that, because o ohms is o ohms... no resistance. This wouldn't play any part in wires getting hot unless the sender itself if shorting out when empty.

Willcox

MBrianB

Since I'm taking the sender out I'm also going to replace it at the same time. Ordered from you Willcox this morning.
Will test the takeout. Shame since it's new.

MBrianB