Bouncing Fuel gauge

[76 3+3]

how about bouncing gas gauge? a fix for that?

[4x4orbust]

if by bouncing you mean it will go from a full tank to 1/4 tank when you stop,  that's because the gas tanks don't have any baffles in them, and the fuel sloshes around pretty good.    i put new tanks in my truck that have baffles and it doesn't do it anymore,  but my gas gauge stopped working about 1 day after i put the tanks in, so it could have been a fluke.

[76 3+3]

thanks 4x4orbust...the fuel gauge worked for over a year with minimal movement (bouncing around from normal sloshing in the tank). now what i see is a jerk like bounce sometimes from half a tank to 1/8th of a tank. it normally does it only when driving or when i put it in drive. while parked and not in drive it still moves slightly but still jerky. im sure i have some type of electrical issues. i have replaced the curcit board on the back of the cluster and new alt battery, checked the ground..not sure what is going on. volts on the gauge when idel is around 13. once lights, fan, and put in drive volts drop off to 8 or sometimes less. lights dim then come back bright..who knows. electrical systems i lack skills.

[DnStClr]

It does sound more like an elect. issue rather than a faulty fuel delivery system. You might have to keep looking for a loose wire connection or loose ground. Begin at the starter, alternator belt, battery ground, and make sure all the screws are installed in the instrument cluster. Some are used in the grounding system. It might be a job of elimination to fix it.

[Josh454]

If your volt gauge is intermittently dropping to 8v and your lights are going dim I would start there first.  If you have already replaced the alternator I would thoroughly test and inspect the battery power and ground cables.  They are cheap and easy to replace.  On a 25 year old truck they are usually shot.  Have you checked the battery connection at the starter?

[76 3+3]

Took the truck for a drive tonight and noticed that gas gauge only bounces when lights are on. When they are off gauge stays in one spot. I also noticed that when I switch to high beams volt gauge jerks and stereo cuts out for a second then comes back on. Fairly sure some electrical issue with lighting. Another thing I noticed was when I put my hazards on with lights off and in park I get nothing. When I press on the brake side marker lights and parking lights illuminate but stay constant-no flashing. Jeez.

Cluster / curcit panel is one I pulled from another 76 and is in excellent condition and wiring harness is good. Positive battery cable is new with good connection as well as ground. Have not checked at the starter but will check that as well. I pulled the starter a few months ago and had it checked. All was well so I threw it back in. 

Thanks for the suggestions Josh454 and DnStClr. 

[Irish_Alley]

i would think the alt would be a problem mine charges at 14.5 with lights on 14.1 and with lights and wipers on its only at 13.9. but my 94 would everyonce in a while jump down to like 10 went to replace it found the neg bolts on the bat was just barley tight enough replaced the alt and tighten the bolt all is good now, get it tested

[tj wand]

my gas gauge does the same thing. but it only bounces when im down to a 1/4 tank