The short is between the switch and the gauge unless both sending units are
Check the valve that switches the tanks and the switch on the dash---the
gauge could be wired to either---have to get a wiring diagram or trace the
wire to tell
Put a quart of carb cleaner in the bad tank and drive it on the good tank
for a couple days then drop it and dump it
replace all ruber fuel lines on both tanks while you are under
there---better under controlled conditions than on the roadside somewhere
The original fuel sender from my 91 Ranger measures 15.0 Ohms empty
and 168 Ohms full. The float is plastic. The replacement cost $82.99
Pull the red tab out of connectors with needlenose pliers to free the
pins to pull out the back through the silicone rubber. Autozone sells
Ford pin replacements.
In my experience circuits are much more likely to be open than
The bed bolts are T55 Torx and there's a taillight connector behind
the bumper and the fuel filler screws to undo before lifting the bed
off. I place a wood spacer behind the cab to protect the paint. It's
an easy one-man job with an engine hoist and a 2x6 cut to fit under
the top rails of the bed.
Disconnect the yellow and white wire from the switch - see what
happens. Then ground the yellow and white wire and see what happens.
On a lot of the later Ford products the guage works backwards from a
Chevy and most others.
Your Ford may well have a guage system that reads full when the sender
is OPEN and empty when it is GROUNDED.
Thiswould make sense on your truck, having sat for so many years -
the very low current through the switch to the senders, and possibly
the contacts on the fuel sender units, are oxidized enough that NO
current gets through and the guage stays pinned on full.
From Advance AutoParts.com:
To test the fuel sending unit, you will need to fill the tank with
gas. Use a multimeter to test resistance. In an old-school classic
with analog gauges, you'll need to know how the gauge works, as
manufacturers used different electrical conductance to operate the
gauge. For example, a Ford fuel sending unit has almost zero
resistance on a full tank, while a GM sending unit of the same year
has maximum resistance on a full tank. Your repair manual will advise
If the resistance reading is off by several ohms, you have found the
culprit. Before yanking out the fuel sending unit, go the affordable
route with a bottle of fuel system cleaner. While there are no
miracles in a bottle, car forums are littered with posts explaining
how an $8 bottle fixed their fuel gauge/sending unit problem. The
float on the sending unit may have become corroded with sulfur from
low grade fuel, and there is a possibility the fuel system cleaner may
resolve the issue. GM technical service bulletin #06-00-89-07BB
specifically states to use fuel system cleaner to resolve a stuck
That's because they are "ford lovers" - they haven't had to workon
That said, I'm on Fords 5 and 6 right now. #1 was a 1976? Granada
Ghia. Then I had an '89 and a '90 Aerostar, and a 1995 Mystique
(Mondeo). Other than rust and a few electical problems on the Mystique
(due to it's British DNA) I was pretty happy with them.
Currerntly a 2002 Taurus and a '96 Ranger.
The problem will LIKELY be in the tank selector switch. The wire
from the guage unit to the selector switch is being grounded
SOMEWHERE. Disconnect the wire on the selector and youwill LIKELY get
the guage to drop. A spdt switch between the 2 tankj senders and the
guage unit will then make it work - independently of the tank switch.
Wieber has said many times that he has electronics skills, and owns
several oscilloscopes. For example: "my electronics shop"
Why would you be giving basic troubleshooting advice to a guy who
claims to have an "electronics shop?" Are you thinking there's some
planet where electronic techs need basic advice on how to fix a fuel
I know a lot of electronic technitians and even engineers who would
not have a clue what to look for on an automotive fuel guage -
muchless on a dual tank system.
Also, the tools most definitely do not make the man - or the
technitian - even if you know how to use the tools.
Fortunatrely I've had a lot of experience inthese things, and I'm
willing to share my knowlege.
Unlike somany who know nothing and are more than willing to share
Techs who claim to charge $75 an hour to troubleshoot and repair
machine controls, but who don't know how to read a fuel gauge wiring
No. If he knew how to use an oscilloscope, then he'd know how to
troubleshoot by read a wiring diagram.
But he doesn't. And here's proof, an independent review of his
electrical troubleshooting skills.
There can be no doubt - Wieber is allergic to common sense and wiring
Oh sure, I can build a plane, but can't fix a fuel gauge. That makes
sense to you? Of course it does. Get a clue. I don't help liars.
Especially deadbeat liars. Doubly especially liars who espouse hanging
people from lamp posts. If only I had the kind of "Christian"
sensibility that allowed me to be OK with hanging millions, eh? Wieber
deserves mocking, not help. The best part is that he's more likely to
claim to have a fuel gauge repair business than he is to ever fix that
gauge. At least we're all the wiser for learning how to use PB Blaster
to fix electrical problems.
Hey, it's only been seven years since it was proven that "tech" Wieber
doesn't know what to do with a wiring diagram.
So what if he hasn't learned since? Maybe he just needs another seven
years. :) Try not to be so impatient. And hope that we aren't culled
before we get to read Wieber's inevitable post asking why flashlight
are often installed in opposite directions.
The EGR position sensor on an '88 Ford will cause that problem, and
being "OBD1" - or technically EEC IV, it will not necessarily throw or
hold a code..
Check the connections on the EGR - also check to be ABSOLUTELY CERTAIN
there are no vacuum leaks in the EGR control system. Perhaps remove
the EGR valve and clean the heck out of it. The postion sensor may be
mis-reading the position, or the valve may actually be sticking
Put your 'scope on the alternator output and check to be sure the
output is constant. NOT LIKELY, but possibly the brushes are jumping
and the charge is intermittent - which on SOME vehicles will screw
with the CEL.
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