And yes, it has some gas in it.........

Brown wire in body harness goes to rear for gauge. Zero ohms is empty, 90 ohms is full.

Take ohmmeter and measure at trunk, drvr kick panel, at sending unit, or behind gauge for ohms value. When at sending unit, be sure ground strap (black wire) is on a good ground, usually at pass side tank strap under trunk floor.

Zero ohms is empty, 45 is half full, 90-100 ohms is full. Console gauges have resistor across gauge connection to calibrate gauge, somewhat, I think. Turn key to IGN and check for voltage to sending unit from gauge and at sending unit, maybe. At least through/to trunk connection.

Could be fuse also.

Everett's tests are exactly what I would do, but we don't all have a meter or know how to use it (tho I suggest you get one and learn how to use it, if you don't, check the electrical basics sticky)

But.... There's an easier way.

In the trunk, center rear, disconnect the tan (brown at this age) wire from the 2 wire connector. Turn the power on. If the circuit is good back that far, the guage will go way past full. (the second wire in that connector is the license plate light, don't mix em up!)

Either way, get back to us.

JIM when i disconnect the said brown wire the gauge goes past full as it should with infinite resistance...I am having trouble with this because I cant find a schematic...

BTW...I am a 10yr Aviation Electricians mate:hurray: ......

On the disconnected tan (brown) wire, what is the ohmic value into the sending unit referenced to ground?

If you read some value of ohms, then the sending unit should be working. Remember the ground wire I mentioned earlier?
Back feed the tan connector referenced to ground and read the voltage from the gauge in both disconnected and connected. Should be the same value. If the voltage drops dramaticly when connected, then not enough volts (current) coming from the gauge, bad or corroded connection from the gauge to the trunk lead.

Driver's kick panel is the body connector from the dash harness to body harness.

I was a Navy Communications tech.

JIM when i disconnect the said brown wire the gauge goes past full as it should with infinite resistance...I am having trouble with this because I cant find a schematic...

BTW...I am a 10yr Aviation Electricians mate:hurray: ......

Then we're on the same page...lol. I was a radar tech in the navy in another life.

Schematics are easy, check the elctrical basics sticky at the top of this forum, find and download the schematics, and pm me for the password to pen them.

Everett, the ohm value at the sender to ground is 24.5. thats about how much gas is in it. When its disconnected the gauge drives past full....

Everett, the ohm value at the sender to ground is 24.5. thats about how much gas is in it.Good, 1/4 tank of fuel. When its disconnected the gauge drives past full....Good, does what it is supposed to do.

Now, you hook up the gauge and it shows zero/empty. I wonder what the voltage is reading?

You might substitute a rheostat, 0-500 or 0-1K, or anything, would be good for the sending unit. This way you can control the gauge and better troubleshoot. Using JimM's sticky on schematics, you can do this.

I would check voltage available for the sending unit. I think there should be a shunt resistor to lower battery voltage to 5 or 7 volts on the back of the gauge or on the fiberboard. You might hook up the DMM as an ammeter and look at the current flow when 1/2-1/4 tankful is selected. Zero ohms will show max current, empty tank. Read available voltage at the trunk disconnected, then the available voltage connected at the trunk, you may have to backprobe the connector to read. If gauge goes to empty, then the shunt resistor may be burnt open.

GREAT!!! AAAARRRRGGGG!!! now the gauge is being tempermental! It just showed me a 1/4 tank! then it quit. What is the black wire attached to the trunk latch housing? It also comes from the same conduit under the latch that the gas gauge wire/lic plate wire comes from? I noticed it was a bad ground....

Ground (return) wire for the license plate light.

Yer getting some weirdness...

Gas guage problems are very common, but for the most part your readings indicate "normal".

There is an article in electrical basics on troubleshooting the fuel guage, might help.

Is this a console guage car?
If it is, send me an email, I'll reply with a different schematic, the one posted is for non-guage cars.
Note the circuit is the same, just different connectors and stuff in different places.

NOW, when I disconnect the sender, it goes past full. When I check resistance, I only get about 8ohms. If the gauge drives past full when 'open', doesnt that mean that my gauge and wiring is good all the way to the sender? Im starting to think bad sender... the gauge drives past full everytime I disconnect it...thanks guys!!!

Should I just say the heck with it and buy a rear body wiring harness? I say this cause my trun signals work but my brake lights dont. Nor does the brake lamps work when I turn the headlights on....This sux...know why? I am on a military installation and they could care less if I am just cruizing my car around because 'the lights HAVE to work...' this sux! I cant drive my car cause the lights dont work...the gas gauge is screwed up...yada yada yada, blah blah blah...(as i cry myself to asleep)

Sounds like the batt ground to the body may be weak as well. I run into this alot with trailers. Try a new ground wire from battery to firewall. If this works you can buy the chassis grounding kit from any repop shop.

Hope this helps

Tail light issues on a 68 are often casued by the tail lights not getting a good ground. New paint in the trunk will do this every time. I get some external star washers and put them under a couple of the tail light mounting nuts on each side. In fact, I use them under every ground connection on the car.

From the sounds of your gas guage, I'm thinking you got some sender weirdness. You might check the ground wire, it is attached to the body on the pass side in front of the gas tank. I'm thinkin yer gonna need to pull that tank out tho.

it could be a bad ground even if my turn sigs are working? I will try to get the tail lights to ground good when i get home tonight...
as far as the gas gauge goes... i should just get a new one and be done with it...

haha, now we're really getting crazy!!!

Your gas guage and wiring are fine. "borrow a 100 ohm pot and a few clip leads to prove it, hook it up in the trunk, one end lead to ground, middle lead to the harness connector where the tan wire goes (tan wire disconnected)..

Study the schematic on the tail lights / brake light / turn signals. Then have someone else cycle the lights thru various combinations while you watch them very closely. The bulbs have 2 filaments, and they are different wattages and brightness. What happens if you have an open ground is, as long as only one signal wire has power, the circuit backfeeds and finds a ground thru the other signal wire. Both filaments glow, but very dimly since they are operating in series. you turn on both signal leads (brakes or turn signals with the taillights on) and since you have 12 volts on both sides of the bulb, the light goes out. This is classic for a bad ground issue, and is very common on 67 & 68's.

It could also be that you simply have a problem with the brake light switch, and everything else is fine.

Also possible that the steering column, turn signal switch, or hazard switch are involved, they all feed the same bulbs thru the same wires.

When people post with these problems, we usually come back with what we see most often (that don't mean we're right this time), there is no substitute for learning the schematic, doing some voltage testing, and giving us all the details you can.

HAHA! the old brake light switch is hung in the open position!! BUT, alas, a new switch didnt change a thing. hmmm can the b/l switch be in backwards?
I checked for pwr at all 4 sockets. no power. hedlit sw on or brakes engaged...but i did notice that when my left turn sigs are on both left rear bulbs light up...with right turn sig on, both right bulbs light up...? is that normal...? or should the turn sigs just light one bulb on each side? this sux!

Clean the grounds on both rear light assemblies. As JimM suggests, corroded grounds.

The rear light bulb socket snaps into the bezel. Each bezel has six studs going through the tail panel. Each stud has a nut with washer to clamp the bezel onto the tail panel. This is the ground path from the bulb socket to body. Remove a couple nuts and clean the stud(s) and tail panel, reattach the nuts.

You might take out the socket and insert them a few times.
When brakes are applied, tail lights, the dimly lit ones, go out. Cuts down on heat generated by the bulbs to prevent the plastic lense from melting.
Turn signal, brake light and emergency flashers use the same wire, the same filament. Tail lights/parking lights use their own circuit.
When a side is selected for a turn, only the bulbs for the side selected should be lit plus dash indicator.
Check all bulbs for the correct bulb part number first.
Back-up lamps are 1156.
Tail & stop lamps are 1157.
Side markers, front & rear, are 194.
Front turn signals are 1157.
Dash indicators are 194.
Turn signal flasher is 512.
Light circuits are designed for these part numbers due to the current drawn by the bulbs.

If this was an F/A-18F, I would have had it fixed by now...lmao
EVERETT, All the bulbs are correct, If my turn sigs work as you say, why doesnt my brake lights work? If they are supposed to work as you state, then I am not getting pwr to the lights....?
I will clean the grnds around the bezel...cross ur fingers...

I "think" it's correct for both bulbs in each housing to light up for brake or turn on 67 & 68, not on 69.

I do not recall that the tail light filament goes out when the brake or signal light is on, in fact I'm pretty certain it does not. Note mine is a 68.

If your turn signals work correctly then the brake light problem is under the dash somewhere, or in the steering column.
What about the 4ways, do they work?

If you can fix an f/a 18 u can fix this.

Jim, what are the 4ways??
none of my marking lights work...(another day)...
Can the brake light switch be installed backwards?

Jim, what are the 4ways??Emergency flashers
none of my marking lights work...(another day)...Markers use the brown wire as power. My book shows power from source from steering column, meaning they flash wiith turn signals. Hmm, I didn't think they did.
Can the brake light switch be installed backwards?Physically, no, unless alot of rework done to mounting bracket. Electrically, doesn't matter. Orange is power to the switch from fuse panel, white is output to steering column for turn signals/stop lights. Remember, same bulb filament for stop and turn.

hmmmm..... might look at that diagram again.
The markers on my 68 do NOT flash with the turn signals, and this has been asked and posted before.

I could be mistaken. Ask my wife, she'll tell you for sure......

GUYS YALL ARE A BUNCH OF d&%m GENIUSES!!!!!!!!!
I just grabbed the tail light socket and a wire broke, so I install a new one from autozone AND THE BRAKE LIGHTS WORK AS ADVERTISED!!! HOOORRAAAYY!!

Now when I pull the headlight switch out, the tail lights still do not work, but the brakle lights and turn signals do, is this a bad ground also?
I CANNOT SAY THANKS ENUFF!! I CAN NOW DRIVE ON BASE DURING THE DAY!!

Could be a bad ground(s) or no power getting to the sockets. The brown wire feeds the front & rear marker lights and tailights.

Brown wire comes from the headlamp switch. Front & rear lights are split at the switch. Red wire feeds switch. PARK position turns on markers and taillights.

Everett, where is this brown wire located? in the terminal connector behind the drvr kick panel?
The front and rear 'markers' are split at the switch?
Using 69-er Schematics...
I checked for power at the kick panel (c200?) and im not getting power except for the orange wire....but I have it at the fuse panel...with switch out or not and key on or off...

The orange wire is feeding your courtesy light, ignore it for this.

I'ma gonna hafta reread this whole mess, my head is spinning... I thought you had brake lights and tail light but no turn signals???

I'ma gonna hafta reread this whole mess, my head is spinning... I thought you had brake lights and tail light but no turn signals???

what happened with the fuel gauge? did it get better?

The orange wire is feeding your courtesy light, ignore it for this.

I'ma gonna hafta reread this whole mess, my head is spinning... I thought you had brake lights and tail light but no turn signals???

I sincerely apologize Jim, It started with a gas gauge stuck on E, you guys helped me narrow that down to a bad sender...

2nd, the brake lights were inop..due to a bad ground/broken wire at socket, which made turn signals work BRIGHTER/BETTER,

3rd is marker lights/tail lights, they have always been inop....sorry for sickness Jim! I am not getting power at connector behind kick panel bt do get it at the fuse....

Cant seem to get the headlight switch out, do I have to remove the dash?!
Thought I might try to see if the headlight switch is bad....again everything is working now except the dash lights, side marker lights, and tail lights-brake lites are good.

thanks to u guys!! these r all I got left to fix!!

Again, I am not getting pwr to connector behind kick panel...but I have it at the fuse box....

Disconnect the battery cable.
Reach up behind the dash at the headlamp switch.
Feel on top of the switch next to the dash panel, a spring loaded button.
Press and hold button down.
Pull out the knob and shaft.
Unscrew the bezel nut on front of the dash.
Pull down the light switch from the rear of dash to below the dash.

Everett, where is this brown wire located? in the terminal connector behind the drvr kick panel?
The front and rear 'markers' are split at the switch?
Using 69-er Schematics...
I checked for power at the kick panel (c200?) and im not getting power except for the orange wire....but I have it at the fuse panel...with switch out or not and key on or off...Brown wire originates at the headlamp switch. Front markers & front park lights are one wire, the rear markers and rear taillights are the other wire tied/split to the same terminal on the headlamp switch.

Power for the switch, red wire, comes from the fuse block. No key/ign needed.

If you have tailights, then the problem is a bad joint/ground between the side tail light and the corresponding marker. Same with front markers, bad joint, or ground, from the front Park lights.

Brown wire originates at the headlamp switch. Front markers & front park lights are one wire, the rear markers and rear taillights are the other wire tied/split to the same terminal on the headlamp switch.

Power for the switch, red wire, comes from the fuse block. No key/ign needed.

If you have tailights, then the problem is a bad joint/ground between the side tail light and the corresponding marker. Same with front markers, bad joint, or ground, from the front Park lights.

I have brake lites.. not marker lites or tail lights...no power at connector ... I have NO interior lights either...

OK Gentlemen, I finally said to heck with it and took apart dash and fuse panel found a bunch of corroded wires. A little wd40 and a rat tail file later, I put it back together and it all works now.

Im saying thanks to Jimm, everett, and 69er for the use of one of his schematics...

Thanks guys!
Harley:waving: :clonk: :hurray:

You're welcome.