[VetteVet]

Originally Posted by 1929fordtudor

You nailed it! 10.9 ohms from switch to alternator unplugged. Yes I have been testing the voltage with the plug installed on the alternator. Ok, now we are getting somewhere! I have 12 volts on the brown wire at the alternator with the connector unplugged. So from the switch to the alternator I have 12.67 volts. So what could be causing the voltage drop when I plug the connector into the alternator? So let me guess, this is normal with the plug connected and I've been chasing rabbits?

According to Ohm's Law a 10 ohm resistance on a 12 volt circuit would result in a current of 1.2 amps I = V/R or 12/10 equals 1.2
Since you are reading an 8 volt drop with a 10 ohm resistance You must have more resistance or more current flow. I would suspect more current flow which probably means a bad diode in the alternator. Are you positive that the brown wire is connected to the no. 1 and not the no. 2 terminal on the alternator?
Check the diodes by using the meter leads between the terminals and ground and then reversing the leads. You should get continuity one direction and not the other. Include the large output terminal in the test.

Originally Posted by 1929fordtudor

On to the fuel gauge now. Gauge tests good and new sending unit by PO. There is no ground to the sending unit and there is no tab or pigtail on the sending unit. Where or how do I connect a ground to the sender if there is no pigtail or tab to connect to?

The fuel sender is configured to ground to the fuel tank which should be grounded to the cab or frame. Then the sender terminal is connected to the fuel terminal in the fuse panel. If you ground the terminal on the sender you will get the empty reading you're seeing on the gauge. Un ground the terminal on the sender and connect it to the fuse panel instead of to ground and read the gauge. Your Ohm range is 0 to 90 Ohms. Take a reading between the terminal on the sender and the sender body (flange) looking for 45 ohms which would be close to 1/2 tank of gas.

Originally Posted by 1929fordtudor

Ok, I attached a ground to the sending unit. There was a very wide tab that I trimmed down to accept a connector. Ran the ground to the frame rail. With key off the gauge is around 10 o'clock. With the key on it moves to just barely below empty. There is approximately 1/2 to 2\3 tank of fuel. Gauge checks out perfectly fine. Could it possibly be the PO purchased and installed the wrong sending unit?

See Above check.