Juppers

I was towing a small trailer yesterday when I noticed my radio dimming on occasion all on it's own. It happened mostly with the brakes applied, but not always, sometimes it would dim with breaks, sometimes it wouldn't dim with brakes. And rarely it would dim without brakes. So I pretty much figured the trailer lights had a short of some sort. A few minutes later, my fuel gauge drops to completely empty and the fuel light came on. I knew I had about a third of a tank, and I was almost at my destination, so I motored on and unplugged it as soon as I arrived. I turned the iginition back on after unplugging the trailer lights, and my fuel gauge returned to correct operation.

I figured I was in the clear, but on my way back home, I look at my fuel gauge, and it is completely totally full and is not budging from there. I have no idea where to start looking to track this one down and fix it. I don't believe it to be a problem with the float valve, I wasn't on any rough roads or hit any potholes or anything. What in the world could the trailer lights have shorted out that would affect the fuel gauge?

DeathCougar

iTrader: (23)

sounds like your alternator may be on its last legs. My truck does the same thing, lights all dim etc becuase its pulling more amps than my alt. is putting out at idle. When I rev the engine a bit and the alt is putting out full power, everything is cool.

You may want to trace all the trailer wiring, and be sure you have good grounds. Also, what kind of wiring was used on the vehicle end?

Juppers

I don't think it is the alternator. Only panel lights dimmed as if the headlights were on, including the gear indicator. That is all fine since unplugging the trailer lights.

I just need to figure out how to get the fuel gauge fixed, and what could make it go from completely empty with the trailer plugged in, to normal without the trailer, then to stuck on full with no hard bumps or knocks to explain getting the float valve stuck.

Juppers

More weirdness. I filled up today, and now the tanks says it is completely empty again. then after a few stops, it showed as completely full for a few minutes, then back to completely empty. I guess if I can't narrow down as to what is bad, I will take it to the dealer and let them deal with it.

Ironmike4x4

Is it just the fuel gauge or the whole instrument panel? My instrument panel went blank and kept blowing fuses, but that wound up being a prank from a tech I work with. It sounds to me like you may have some sort of wiring problem from the fuel sending unit and possibly the resistor in the level sensor. As far as the trailor lights... from what I've seen at work it may be a totally unrelated thing, somone has wired something wong, or a short to power or ground somewhere. If you know how then try to get a resistance reading from the fuel sending unit level sensor wire, (I don't know how you are as far as driveability and electrical diagnosis). Yes it will be a PITA to get to, but it will save you from having to drop the tank before condemning the sensor.

Juppers

It is only the fuel gauge, everything else is working correctly. There are no blown fuses in the engine compartment or in the dash fuse panel.

I will see if I can hunt down a schematic to get that resistance reading. Hopefully there is somewhere under the dash I can reach it instead of crawling under the thing.

Kschempp

I have a fuel gauge that does not work properly on my 99 4runner. It seems to have started after hooking up to my trailer, which I have done many times previously without any problems. The gauge either reads full, or empty and sometimes the low fuel warning light flashes. I read a post a while back where someone else had a similar problem, but I can't seem to find the post. I am new to the forum and would like any help you can offer.

Juppers

My problem was a blown resistor on the back of the cluster. I bridged it with solder and its worked fine ever since.

Kschempp

Which cluster are you referring to? Is it the instrument/gauge cluster behind the dash?

Juppers

Yes. The instrument cluster with the gas gauge and the speedometer.

ALLDATAdiy INFO

If you have a test lamp, the factory testing in ALLDATAdiy can tell you if it is the gauge or the circuit.