Blowing gauge fuse and now a P0500 code

So last week I drove my 1998 Tacoma, 5 speed 4X4 non ABS a few miles and I noticed that my speedometer had stopped working. Then I realized that none of my gauges were working. I replaced the blown gauge fuse and drove on. Later that day the gauge fuse had blown again. This time I noticed that my windows would not roll up or down, and my fan would not come on as well.
I came home, replaced the fuse, poked around under the dash half the day, but found nothing. Then today as I was driving and my speedometer stopped working, but the rest of the gauges were fine. The windows worked and the fan worked. Then my Ultragauge alarmed and it displayed a P0500 code. Shortly after that the CEL came on and a little while later all the gauges went out again.
I came home, replaced the blown gauge fuse again, unplugged the vehicle speed sensor plug and went for another test drive. About five miles into the drive the P0500 alarmed on my Ultragauge, but no CEL and all the other gauges continued to work. I drove about 10 miles and nothing else happened. With the VSS disconnected, I'm curious how the ECM would know to throw a code and not light up the CEL.
Does anyone have a clue as to what may be the issue?
Thank you.

 

Tested and replaced the speed sensor, still blew the gauge fuse.
Disconnected the aftermarket trailer wiring harness, still blew the fuse.
Unplugged the connector at the reverse switch on the transmission, I'll drive it around and see if that does anything.
I'm hoping it's not the gage cluster itself.

 

Drove about 30 miles on and off road with the wiring connector removed from the reverse switch on the transmission. Fuse didn't blow, even after placing in reverse and backing up a few times.