Turn sig,fuel sending ghost??wth?

[dezdud]

Ok. So my gas gauge pegs over way past full when its full and shows 3/4 full when it's empty. The guy i bought the truck from put in a brand new gas tank and sending unit. When i put on my headlights,bright switch, the gas gauge slamms all the way to the left?? and seperatly, if i put on my left turn signel, the gas gauge needle moves back and forth with the signal, as well as my little red high beam indicator light going on and off in unisen with the signal??/ omg..wth? (the brights and turn signal do function though even with all that stuff going on)..????

[CC69Rat]

Sorry man .. we're gonna need a video of this please.

(kidding) Welcome to the forum! Seach for a guy on this forum, his ID is VetteVet or something like that. I'll see if I can find him for you. It sounds like someone has wired something into the back of your dash bezel, or used a wire for another purpose .. radio install, or something that's just not quite right. I had similar issues with my GMC and helped get it figured out. Ex. When I turn the dimmer switch for the dash lights, the headlights would dim too. It sounds like a wiring issue.

[bonnieclyde100]

check all your grounds first because bad grounds can make everything work funny. for a while on my 94 chevy when ever i turned on the AC the speedometer would read wrong but i turned it off it would read correctly .

[dezdud]

Ok. I'll check ground. It was recently painted though,and i know they/he,took out the dash instrument cluster and installed a radio. (painted inside of cab,dash etc). So i'm thinking somebody just hooked up to the 1st hot thing they found???

[GCncsuHD]

I agree with the ground suggestion, bad grounds can cause funny things to happen.

[panhandler62]

The suggestions on checking that everything is properly routed to ground are good ones.

When an instrument is not correctly routed to ground there are cases when the current will find a ground path *through* another instrument. You'll swear the dang thing is haunted!

[dezdud]

Haha...Ya, it's haunted alright.! I will go ground hunting 1st. Thanks.

[VetteVet]

Originally Posted by dezdud

Haha...Ya, it's haunted alright.! I will go ground hunting 1st. Thanks.

First off you need to make a signature and tell every body what year truck you have and what engine and trans so we know what we are dealing with. I searched your posts and see that you have a 69 so that helps a bunch.

It's really hard to tell what is wrong when someone has been rewiring stuff so it is easier to show how the wiring should go.

The first problem you have is that the fuel gauge is not getting a ground from the sending unit and as the others have said, it is hunting for ground through the dash circuit, mainly the high beam indicator light and the turn signal light. When it doesn't get a ground it will go way past full like it's doing.
Do you have the battery gauge dash or the idiot light style?

Look on the fuse panel on the right edge and you should see a brown or tan wire going to a terminal labeled fuel. This is the ground wire from the sender in the tank. If it's there then run a jumper to the nearest good ground and watch the gauge with the key on. It should go to empty. If it doesn't then run the jumper to the fuel gauge or to pin 4 on the cluster plug. There should be a pink wire on the no 3 pin of the cluster plug for a battery gauge dash and if it's an idiot light gauge the pink wire will go to the no 7 pin. This is the power wire for the cluster and since you are getting past full on the gauge I'd say it's on the right pin.

Here is the gauge cluster plug connections.



Here is the wiring for the cab and the dash cluster for the idiot lights in the right center of the diagram.



Here is the fuse panel and you can see the sender connection from the fuel tank. This one is on the left end. some are on the right end.

[dezdud]

^^^ KOOL dude. Thanks.!!!

[dezdud]

Oh, and my dash has all the gauges,like 7 holes or something.

[70STOVEBOLT]

I have a similar problem, but not exactly the same. I have the issue with the turn signal causing the fuel gauge to move in unison but both left and right signals make mine do it.
Also, my fuel gauge does not go to 3 o'clock unless I unplug the tan sending unit wire from the sending unit on the tank. After the key is shut off, the fuel gauge does climb to around 3/4 full after a while. Still sound like a bad ground issue? Thanks in advance for any help.

[VetteVet]

Most likely your turn signal bulbs in the dash are not grounded well and they are grounding through the fuel gauge sending wire. The easiest way to check this is to remove the bulbs in the dash and see if the fuel gauge stops cycling. Do the dash lights work?

Pulling the tan wire on the sending unit should make the fuel gauge go past full so that is normal.

The small coils in the fuel gauge are designed to pull the needle towards full or empty depending on the resistance in the circuit. They also are set to leave the gauge needle at the last setting when power is shut off the gauge, so they sort of balance between full and empty. As long as the gauge reads correctly when power is on there is nothing to worry about.

[70STOVEBOLT]

The dash lights seem to be working normally. I think the fuel gauge is reading incorrectly though, because I had a little over a quarter tank last I remember and now it reads empty.
Usually I can tell if I still have a little in there when it's on empty, by swerving back and forth and watching the needle move with the slosh. But this morning it did not move when I swerved back and forth ( this was at low speed, with no oncoming traffic, of course). I am going to check the tan wire, I did change the seatbelts yesterday, maybe I pinched the tan wire and it is grounding out?

[70STOVEBOLT]

Ok, I'm pretty sure it's a ground issue with the tan wire. As I mentioned, the gauge goes up to about 3/4 full when I turn the key off. Yesterday when I opened the door to get in, I noticed it jumped up to about 7/8 and when I closed the door, it went back to 3/4. I did not have time to check it out last night but this morning I stopped and put about 10 gallons in it and the gauge now reads about 1/2 tank with the key on, but it jumps around even when sitting still after it stops sloshing it moves back and forth. I am going to remove the sill plate and check it out tonight. Hope it's just grounding out.

[VetteVet]

Originally Posted by 70STOVEBOLT

Ok, I'm pretty sure it's a ground issue with the tan wire. As I mentioned, the gauge goes up to about 3/4 full when I turn the key off. Yesterday when I opened the door to get in, I noticed it jumped up to about 7/8 and when I closed the door, it went back to 3/4. I did not have time to check it out last night but this morning I stopped and put about 10 gallons in it and the gauge now reads about 1/2 tank with the key on, but it jumps around even when sitting still after it stops sloshing it moves back and forth. I am going to remove the sill plate and check it out tonight. Hope it's just grounding out.

That's a pretty common place for the tan wire to ground. The sending unit float can get pin holes in it and let gas in which makes it heavier and that will cause the gauge to read lower than it should.