10 amp ignition fuse popping

I have 2008 toyota tundra 4WD. The 10 amp ignition fuse keeps popping. The fuse is connected to air bag system, engine immobilizer, cruise control and multiport fuel injection circuits based on my research. I tried to disconnect each of the systems, start the truck to see if i can isolate the circuit that is shorted. First I disconnected the air bag circuit (the yellow junction under the driver seat), still pops the fuse. then found the engine immobilizer fuse and disconnected it, still pops the ignition fuse. i also disconnected the connectors to the cruise control, did not make a difference. Any suggestion folks?

 

To rule out electrical surge, disconnect the battery and then replace that fuse again to see what happens. These trucks can be sensitive.

 

Thank you, Tundra 234. I definityly will try it early in the morning. Are you suspecting the battery may be sending a large Amp through the fuse...

 

Does it only pop as soon as you turn the key on? Or is it as soon as you plug a new fuse into the socket?

Knowing this can help track down the problem/trigger for the overload in the circuit.

 

It pops when I put it on the start position. I checked in off, on, and acc position it does not pop. As soon as I turn it to start, it cranks, almost starts but not quiet, that is when the fuse pops

 

I don’t know if this helps but 4hi and 4lo lights keep flashing after it pops

 

2 Things you may have a loose ground or an exposure along the ignition wire. You may need to manually inspect the wire from point to point. Not the same, but I had an exposed wire on my fog light and every time I would turn the lights on the fuse will pop. Turned out a small nick was exposing the copper wire and would short out.

 

Blackdemon…. Interesting you say that, I tried to install a fog light a few weeks ago. I was not able to complete the job so left it alone for a while. The truck was working after that.


When you turned your fog light was the ignition fuse popping?

 

It is also connected to the brake light switch which is down the the brake pedal. You could try unplugging it and replacing the fuse on the off chance the switch is shorted out.

Most likely will have to follow the main power wire from the fuse around the truck looking for damage. Rodents maybe? If any part of the insulation is missing and the wire is touching metal the fuse will burn up every time.

 

Wait what all did you move/change wiring wise when you were trying to do this?

 

The previous owner had installed a relay and wires for the fog light. I did not add new wires.. I tied to use what the previous owner set upbut it did not work. I disconnected all the wiring the wiring.

 

I tried disconnecting the brake light switch. The car started and the ignition fuse did not pop. I connected the brake light switch back. The ignition fuse pops every other time I try to start the car (intermittently pops).

 

Sounds like you have a bad brake switch to me. Not really expensive or difficult.

 

Sounds like you may have shorted a wire portion of the wire. I would check wiring for continuity, check cyl 1 and sort of track it from there in search for damage.

This was my Celica andnit's fog lights were installed from the factory, damage to the wire coating was enough to short it out

Another example my SC400 was giving me stalling issues. Decided to jump my fuel resistor, but after some time it fried the wire at the tip and left me stranded at a gas station. Had to remove the rear seat and got the cops called on me.. Anyway clipped the tip and reinstalled the OEM harness as that wasn't the issue, but I'll drop these images for context.

 

Thank you, Blackdemon. What do you mean by cyl 1? I will do that and keep you posted on what I find.

 

Thank you, Blackdemon. What do you mean by cyl 1? I will do that and keep you posted

 

I believe ignition is based off of cyl 1 for advance and retarding of timing. If cyl 1 is not at Top Dead Center you don't get engine noises. If it's damaged you may get a misfire or failure to start.
best advice would be to download the wiring diagram for the ignition on the EWD section here and trace that wire. Check the grounding point and allbother points along the way from the fuse box, relay to the other points. Key ignition, Cyl 1,

 

If the fuse is not burning itself up with the brake light switch unplugged then the break you created in the circuit by unplugging the switch isolated the problem.

Your issue is from the brake light switch to the end of the circuit. The fuse is good meaning the wiring from the fuse box to the switch is good, the problem is after the switch.

I would be checking all the bulbs in the taillights just to be sure. Also a chance your brake light switch failed internally or there is a completely different issue somewhere in the line.

Do you have more history as to when this started? Was it just one day randomly? Was it right after someone attempted to add in fog light wiring? The question is did something fail in the truck or did someone make changes somewhere create this separate problem.

 

You could also just remove the brake switch and test it with a multimeter pretty easily and determine that the switch is either good or bad. Like the post above said, start troubleshooting at the known point of the issue and keep going until you figure it out.

 

I would agree with the above to post, but the brake pedal grounds the starter relay, which allows the grounding to ignition and to start, I would agree a good starting point would be at both stalks behind the steering wheel, followed by the rat's next behind the lower dash panel. The ignition would start from the ignition switch, I would check the grounding point possibly behind that lower dash panel, if no issues there, will have to be followed under the hood. I'm a drop some PDF files you will need to look through them and follow the rainbow through its paces for spliced wires, or possibly damaged switches.

 

Thank you guys. The problem started one morning. It run fine the day before. Would crank but not start. Looking around I found the ignition fuse blown. No work was done on the truck the day before. There was a fog light wiring (but no fog light) when I bought the truck 3 yrs ago.I installed fog lights 2-3 weeks ago and tried connecting the existing wiring to the fog light. It did not work so I did not pursue it further. I disconnected the fog lights from the wiring and the lights are not attached to any circuit now.

 

I took the brake light switch out and tested it with multimeter. There is continuity between the two large studs when the button is depressed. The smaller studs have no continuity and read high resistance with the button depressed it not depressed. Does this mean the switch is bad (the finding on the smaller studs)?

 

I need to correct the continuity is with the button not pressed

 

I am here to report on what I found and thank everyone. I have to say there are wizards and wizardeses (is that even a word?) in this forum. Blackdemon… you are one. Jeff 5_7… you are great!

here is how I went about trouble shooting the problem.

1. Using multimeter in continuity setting, I touched the positive battery terminal to good body ground, I found there is short to ground

2. then, I kept doing the same all the way to the output side of the fuse (the other side being the side attached to the battery side) which kept popping. There was short to ground there too.

3. I studied the wiring diagram and identified the 4 circuits the fuse (10 amp ignition fuse) protects. I kept testing individual circuits for short to ground.

4. I found 2 wires in the harness going under the top part of the radiator harness.

 

Here is I think how it happened.

As you can see the radiator support has been bent before likely from an old accident. About 3 weeks ago when I took the truck for oil change the mechanic had hard time closing the hood and he told me he had to make some adjustments, in addition when I tried to install the fog lights I manipulated the wires going to the lights which is also close to the harness which had the short. I also put zip ties to secure the wires hence making the contact between the bare wires and the body. Happy to report the truck is running great! Thank you guys!!!!

 

And gals.