Electrical Question Re Fuel Gauge

[eightbanger]

Where do I start? I've had this 71 Cheyenne about 3 weeks now and im trying to get the most obvious faults delt with for now. My fuel gauge is not working, i've looked at he sender and all seems fine, I also am not sure were the needle should rest on the dial...if I fill it up is the needle supposed go all the way to were it is now in its stuck position? and when it is empty will it travel all the way back past the word empty to the bootom left of the dial? or should it just stop at the words FULL and EMPTY?


Here's the next part of this question, can anyone tell me from looking at the pics if these disconected wires at the fuse board are the problem, should the Orange wire go to the board where it says Fuel Gauge, or should it be the Pink one, or should they be joined and both go there????????



I have zero idea when it comes to electrics, and im not going to start touching things together under there until someone says I can.

Thanks.

[suville]

There is a color correct wiring diagram I believe in FAQ section, maybe someone can verify. I printed it out for my shop reference. Whoever put it together put some time into it! Thanks. Steve

[greasy68]

The needle should stay between the Full and empty words. Your gauge is not working properly. I'm not sure on the wiring but take a look at the wiring diagram like suville said. That should get you on the right track. Your truck looks a lot better than mine under the dash despite the unconnected wires. You should have no problems figuring out where everything goes if you use the diagram.......the problem will be finding out why they were disconnected in the first place. On my truck everything that was disconnected was because it had problems. Dig in and have fun.

[haysonj]

orange wire is Cig lighter or AC. Pink could be fuel sending unit, when needle goes all the way down it is usually the sending unit or a bad ground at the tank.

[haysonj]

orange wire is Cig lighter or AC. Pink could be fuel sending unit, when needle goes all the way down it is usually the sending unit or a bad ground at the tank. Look at the wire on your sending unit at tank if it is same size and color then connect the pink to fuel gage.

[lks dcvn]

Well...

the stock color for the tank sending unit is tan (like the one circled in the pic below)...notice circled green area near bottom. This is true of all the 67-72 trucks that I have owned...

I would not start plugging anything into the fuel gauge portion of the dash wiring harness UNTIL I knew what it was (and if it had a current)...nobody needs to burn down their own truck.

Trace the wire from the tank to the dash and see what color wire runs from the tank to the harness (following it to make sure of no grounding spots or color changing wire splices).

If the wire is unhooked from the dash wiring harness (like yours is) - you will see exactly what your fuel gauge reads...

[eightbanger]

Thanks folks...

[BLACK AND BLUE 67-72]

The wire that needs to plug into the fuse box is tan and it will run back under the driver's door sill plate.

[soba_03]

I agree trace the wire (tan) from your fuse box back under the drivers sill plate to the tank. It Should hook right into your sending unit.

I have also found that if the battery on your truck is bad (like mine was last weekend) your gage will read off. I had a dead cell in the battery. Worked fine when weather was warmer and even started fine, drove it for 30 minutes left it sit for about the same length of time, (OAT was +6 Deg) went to start it and it just clicked. New battery and everything worked fine including fuel gage.

I would say that possibility exists that the wrong wire is plugged into your backup lights. There was a Schematic in the frequently ask questions portion of this site at one time. You may want to look there.

Regards!

[soba_03]

OK I just went and checked, YES there is a COLOR schematic in the FAQ of this site. I'm NOt sure that the link I'm about to post will work. But if you got to FAQ and search under truck tech FAQ it's there.

Here goes


http://photobucket.com/albums/d159/b...nd-chassis.jpg

Ok so it doesn't work as a link. Cut and paste it in the browser address line it will take you to a location where it is. And again it is o the FAQ of this site too.

Regards!

[eightbanger]

I've studied those color wiring diagrams in the FAQ section, till im cross eyed, and it is definate that a tan wire runs from the instument cluster to the fuse box, then tan again fom the same point on the box all the way to the sender on the tank.....tomorows Saturday and i,ve now got my project for the day.

I just had a thought, petrol & spark make it go, i'll be messin around with the same two things tomorow only in the wrong place, I might get launched straight up instead of forward.

A big THANK YOU to all of you who have helped me with this.

[soba_03]

Ok here is something else to think about. When I was having problems with the fuel gage. GOOGLE search 68 or 72 what ever year truck it is fuel gage testing. It should give you some feed back. I got some stuff off the web that said if your ground the sending unit to the body gage should run to the empty side. If you ground the sending unit to the tank it should run to the full side. I don't recall which is which. It sounds scary (trust me) But it is really ok. It tell your that your sender is fine. I don't remember which was which.

If you don't have something plugged into your (fuel gage) location on your fuse block there is about a 99% chance that your problem begins there.

Wish I was there, you could wait in the house for the (boom)...LOL

I'm kidding, Good luck....

[byrd]

To test the wiring and the gauge, unhook the tan wire at the tank and the gauge should read past full(not as far as yours but a little past) and if you ground out the tan wire to the tank the gauge should read past empty. If you have a mutimeter the sending unit should read between 0(empty) 90 ohms(full), that way you can say if the sending unit is working properly or not. I have a ton of gauges and parts laying around if you need something just PM me and LMK.


Randy

[soba_03]

Byrd, can you fix amp gage? Doesn't move and it doesn't appear to me a problem with circuit board...I'm stumped..

[VetteVet]

Here's a site for troublshooting the fuel gauge. It applies to the later trucks as well
http://www.6066gmcguy.org/Electrical-02.htm

[eightbanger]

Originally Posted by VetteVet

Here's a site for troublshooting the fuel gauge. It applies to the later trucks as well
http://www.6066gmcguy.org/Electrical-02.htm

Thanks mate, good site.

[byrd]

Originally Posted by soba_03

Byrd, can you fix amp gage? Doesn't move and it doesn't appear to me a problem with circuit board...I'm stumped..

Check the two football shaped fuses that are under the hood, one is near the battery adn the other is near the voltage regulator. Both should have 3-4 amp fuses in them. If the fuses are good then most likely the gauge is bad, at least in my experience anyway. If you have never seen the gauge work you need to trace the wiring for the ammeter and make sure it is intact and test it for continuity to be certain.

[soba_03]

Byrd,

What if it has internaly regulated alternator? No voltage regulator any more. That might be my problem...

[eightbanger]

Ok just to let everyone know, I used wiring diagram from the FAQ and I used the trouble shooting guide and went through all the procedures, to find out the sender was fryed all along.

Thanks again for all the help.

[MT1972cheyenne]

By far the most common place to look for fuel gage problems is under the Drivers side sill plate. The tan fuel gage wire under there commonly gets damaged there by years of crud buildup, etc.