I just picked up a 1970 Olds Cutlass Supreme convertiable.The driverside brake lights don"t work.The other side works fine.There is power going to them and taillights work.There is power going to my gas tank but still no gas gauge.Any help would be nice,Thankyou!

 

Brake light sounds like a bad lamp. Gas gauge operates off of ground.

 

Fuel gauge troubleshooting has been covered in many threads on this site. Do a search and you're sure to turn one up.

In short, "power going to my gas tank" doesn't mean anything. Power from where?

Pull the fuel gauge wire apart at the connector at the rear of the car. It should be under the bumper in the license plate area, and the wire is probably orange. Ground the side from the gauge and turn the ignition ON. The gauge should immediately go to E. Remove the wire from ground, and the gauge should immediately move to F or more likely well past it. If these things happen, your gauge is fine.

Next, make sure the other wire coming off the sending unit, the black/ground wire, is firmly connected to the body or frame where it attaches and make sure the attachment point is not dirty or corroded. You'll probably have to get well under the car to find this wire.

If the ground is fine, then the problem is the sending unit itself, and that means possibly dropping the gas tank to get at it. I don't know about your car specifically. It might be possible to get at the sending unit without removing the tank.

 

It's actually Tan and the connector is within the trunk, not below it. The connector is easy to follow and attaches to the rear harness to the left of the latch area. There is a grommet upper trunk floor which the wire passes through on its way from the sender to the wire harness. There is also a small black plastic quik latch that secures the tan wire behind the bumper.

The ground wire for the fuel sender comes out the front of the tank and is secured to the right side of the rear floor panel upright section. In order to get to this, you'll need the rear of the car up at least 15-17" unless you're really skinny. (Also make sure you place jack stands under the frame for personal safety) The ground is in a corrosion area so I'd remove the screw, clean the area, connector lead, screw and reconnect. Then spray with some undercoating or paint to seal against moisture or further corrosion. There is another electrical ground connection for the rear harness that attaches to the latch down for the trunk. Check it and make sure it's clean too.

re: Brake lights. Make sure both of the 1157 bulbs in the tail lights are working. Test them in the sockets you know work. It's possible you may have 2 bad socket connections in those tail light buckets.

If that works, good. If not, test the 4 way flashers to see if the problem may be related to the turn signal switch.

Look in the trunk on the upper left side of the inner deck. The main rear light harness connector is clipped up there. Check the ground clip on it. Wiggle the connector leads. You might have some corrosion going on there. Pull that connection apart and check for corrosion inside the connector. Finally, track down the left tail light bucket wiring connection and wiggle it, or pull it apart and check the connections for corrosion.

Any areas of corrosion you can clean with a small wire brush and electrical contact cleaner. Use a bit of dialetric grease when reconnecting them to avoid the problem recurring.

 

The reason the OP is reading 12v from the wire to the tank is because he lost ground somewhere and it's feeding through the gauge and has no load.

 

Makes sense. That means he has an open circuit, and his gauge should be stuck on F or well past it. I wonder if it is. He says he has "no gas gauge." We have no idea what that means.

 

Which is why I also gave him the 3 locations where most of the grounding issues for his car will be.

You're right. "No gas gauge" can mean several things, but in this case I think he's referring to an existing gauge that is not functioning properly. The rear main harness connector will cause that loss of ground really easily.

 

Thanks for all your help.My tail lights were bad ground.Gas gauge ended up beimg the gauge ,all fixed!

 

Happy Cruising - glad it's all behind you now. Don't forget what happened and the fixes because it may just happen again - especially with these old cars......