Electrical Prob no one can figure out

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12-14-2008, 05:54 PM

#21

JC_ez

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Quote:

Originally Posted by 98runner210

where is the factory grounds at? i want to check them and maybe scuff them up a bit. Why wouldn't the bumper be a good ground? it is chrome and goes directly to the frame.

No need to scuff up the paint. The grounding is done via the threads of the bolt with the nut on the body (lots of surface area for electrical transfer).

As Gerdo mentioned, the most likely cause for your fuel gauge reading getting messed up is because the bumper is connected to the frame and the 4Runner's frame is not connected to the negative on the battery. The battery negative is only connected to the engine block (which is isolated from the frame via rubber mounts) and the actual body (which is also isolated from the frame via rubber mounts). The current drawn by your lights tries to find a path back to the battery negative, and is most likely travelling through the fuel line electrical system (fuel tank is bolted to the frame).

If you really want to ground things to your frame you should find a pre-welded nut on the frame and use a thick cable to connect the frame to a good pre-welded nut on the body. Make sure the connection is clean.

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03-15-2009, 10:08 AM

#22

98runner210

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Quote:

Originally Posted by Gerdo

Between the nice highly conductive chrome bumper and the frame are a couple of painted/coated mounts. Also I believe that the frame on 3rd gens don't have a direct ground wire (battery to body and body to engine only)

You're probably getting a ground thru the fuel lines and sending some voltage to the fuel sending unit.

Run a ground wire to a bolt on the body and you should be good.

Update: You were exactly right. After my wreck i had them put a new valance on and moved the lights to a bullbar. I moved the grounds up to the ground on the inner fender next to the battery and now the gas gauge is fine when the lights are on. Thanks!