Troubles with gas gauge, speedo fan, e brake

[WIDESIDE72]

I am having trouble getting the gas gauge speedo and fan working in my dad's 71 GMC.

The gas gauge read 1/4 way past full. I checked the sending unit wih an ohmeter and the meter moved when I moved the sender. I tried a different gauge with the same result. Could the wire be bad/ broken?

The speedo cable seems to be seated into the back of the speedo and into the trans. I can turn it by hand...???

I can hot wire power from the battery to the blower and it works, I am getting power at the fuse, I tried a known good fan switch...

Also the brake light stays on after I replaced all of the instrument cluster lamps. THe e brake pedal is way down to the floor. I suppose I need to tighten up the e brake cable (?)

[dmack91]

1. Sending unit - if the gauge is at 3 o'clock, you have an open circuit. An ohmmeter from the sending unit stud to ground should read 0-90 ohms if the sender is ok. From what you are saying, it sounds like the sender is Ok. If so, check the wire from the sender to the fuse panel. If the gauge is working, it should go from 3 o'clock as it sits now, to 9 o'clock when you ground out the sending unit wire. Make sure the wire is connected to the fuse block and isn't shorted out first.

2. Speedo cable - what is the issue? If the speedo isn't working when running, the cable is probably broken inside. To check, disconnect both ends and turn one, the other should turn too. You can also pull one end out a couple of inches and see if the other end moves in at the same time. If either of these doesn't do as I described, the cable is broken. Cheap fix - $15 at NAPA.

3. Fan - not sure on this one. I believe there is a resistor inline, but you would have to check. Sounds like you have an open circuit somewhere.

4. Brake - if the pedal is to the floor, there is supposed to be a spring that goes from the firewall to the top of the pedal. This spring returns the pedal to the up position (on mine at least), and that is what also works against the brake light switch (plunger type). If he pedal isn't going back to the up position, the switch is activated. The e- brake works independently of the hydraulic brakes.


Good luck.

[cdowns]

the brake light has nothing to do with the emergancy brake in 67-72 chevy trucks// the brake light is controlled by the switch on the proportioning vallve and indicates a problem in the hydraulic brake system

[WIDESIDE72]

Originally Posted by cdowns

the brake light has nothing to do with the emergancy brake in 67-72 chevy trucks// the brake light is controlled by the switch on the proportioning vallve and indicates a problem in the hydraulic brake system

That's what I thought as well. I recently replaced the rear wheel cylinders and mastercylinder and bled the brakes all the way around. THe truck stops fine, but the brake light is on. Does anyone know if the light would be on if the wire that plugs in to the prop valve were broken or unplugged, or is it the other way around (ie, on a porpoerly functioning brake system, the wire were unplugged, making the brake light come on)?