Technical wiring help

ok so its been awhile since i have wired a car but i am rewiring a 49 chevy with the ez wiring harness. it has a mustand gas tank with sending unit. with the key off the wire thats suppose to go to the sending unit is dead. with key on my test light is showing a very dim light. so there is some power going to it. my question is does that seem right?

 

the gas tank wire should be dead with the key off

 

Sending units are a variable resistor that read Ohms through them The applied voltage goes through the resistance to ground so your test light will be brighter/dimmer with the level of gas in the tank.

 

Gauge gets power. Ground comes thru sender to gauge. Sender flange MUST have good ground, which passes thru sender kind of like a dimmer switch affects a bulb.

 

ok so the wire coming from the gauge and going to the sending unit should have power with the key on correct?

 

it should have some power, but not full power. It's not something you should be testing with a test light.

also, the sending unit needs to match the gauge. If you're having issues with how the gauge works, they might be mismatched.

 

ok i undertand now. thank you so much for everyones help. i just didnt want to hook it up and have a major problem or have a fire on my hands. again thank you so much

 

Not really 'power'. The light WILL light, but only because you are completing a circuit with the resistance of the light bulb. You will notice, too, that the gauge will register slightly as well.

Cosmo

 

No.
If disconnected from gauge, there should be NO voltage coming thru wire from sender. That wire provides ground thru a variable resistor to the sender pole of the gauge.
You can measure what is coming thru sender and wire, but it will not be volts or "power".

 

Your gauge is a V coil style AC brand magnetic gauge. There is a ground connection through the gauge to the mount plate and one through the secondary coil to the sending unit. It is the balance between these two paths that determine the amount of electromagnetism that is created and thus, how far the pointer deflects. You should have continuity through the system at those points, but a test light tells you very little. Be sure that you have a 30 ohm sending unit in good condition and obviously that it is well grounded.