Truck Won't Start with Tow Tail Fuse Installed

I finally got around to hooking up my car trailer to my 2018 Tundra SR5 TSS Double Cab today. I noticed that the running lights on the trailer weren't working so I started by troubleshooting the connector (got it cleaned up but no dice) and then moved on to checking fuses. Sure enough, the TOW/TAIL fuse was blown. So, I took the spare 30A fuse and put it in. After I did that the truck would turn over (and over and over) but never start. The message on the dash was something about the start system being disabled and in error (I didn't catch the exact error as I was in a hurry). The problem was resolved by removing the fuse. Of course I still have no running lights on the trailer and the trailer brake doesn't work either.

Anyway, has anyone ever run across this scenario?

 

Where is the spare 30a fuse from? Maybe that’s the starter?

 

No, not from the starter.

There are 4 "spares" for fuses in the fuse box. Don't get hung up on the spare.

 

Occams razor haha, I had to ask .

Next guess is there is some short in the tail causing the original fuse to blow and creating a new crank issue.

 

When the truck cranks and doesnt start its not reading the security chip in the key. Does you trailer have LED lights? They can sometimes cause and issue because there is not enough resistance in them so the truck doesnt know they are there.

 

On this line of thinking ^^, did you happen to leave the key in the ignition while troubleshooting and replacing the fuse? Leave a transponder key in long enough with the ignition off and somehow the security module will ignore it and not allow a start. Take the key out, put it back in, truck should start.

 

No, the key was in my pocket. When the trailer lights didn't come on, I worked through the simple troubleshooting steps. Connectors at the trailer end then the truck. Once those all seemed in order, I moved to the fuse box. That's when I discovered that the TOW/TAIL fuse was blown. Obviously that was the "Aha!" moment. I swapped in a good fuse. I tested the trailer lights by turning on the headlights. Once I did that I saw that they worked and then turned off the headlights. At that point I closed the fuse box up, closed the hood and then proceeded to load the car one the trailer. That took a bit to get everything done there. Probably 15-20 minutes later when I went to start the truck I got the situation where the truck would turn over but not start. Obviously it worked when I parked it to start this process. After pulling the fuse, the truck started right up.

 

Wonder what happens if you install the fuse while the truck is running?

 

That's a good question. Unfortunately I don't have the truck at home right now. I took it to a friends house to get the car it's hauling and the truck out of the way for a family gathering. I've thought of giving that a try as a troubleshooting step.

 

Is there any chance some sort of after market anti theft device has been installed?

 

Not from anything I can find. The truck is totally stock under the hood. Like I said, the original fuse was blown so my suspicion is that there is a problem elsewhere (obviously).

 

OK, yeah, the trailer does have LED lights. One thing I have not tried is disconnecting the trailer and putting in the fuse and trying to start it. However, even with the fuse blown, the truck shows the little trailer symbol on the dash with the trailer plugged in. The brake lights and turn signals do work on the trailer.

 

My suspicion is that this is the case. The original fuse being blown would indicate a problem down the line somewhere for sure.

 

I would guess any demobilizer would be under the dash ...and highly visible. At least the wires outside of the looms.

 

Yep, definitely nothing there. This truck is a one owner and the previous owner definitely used it as a work truck. Other than the factory bells and whistles, he didn't do anything to it.