recently my fuel gauge and temp gauge started spiking past the point of no return , if i shut the ignition off for a second and turn it back on it is ok but intermitantly spikes back up both gauges at the same time , pita .
When my fj62, (long gone now) did this, very soon after it started the alternator went out. Dunno bout the BJ set up? But you might drop by a parts store and see if you have the correct out put from your alternator..
I nearly craped my self when my hj60 did this. Simple fix though, left boot carpet, unscrew fuel sender cover, clean earth on sender and you are on your way. The temp and fuel gauge use the same earth. Hope this helps.
Have you read this thread on common problems/fixes?
My 62 does this when I'm on the freeway for a while. It will spike, then return to normal several times. I haven't tried this fix yet but intend to when I install a new radio and have the dash disassembled.
Very common problem, and very common thread. Pull the instrument cluster and clean the ground contacts on the back of the fuel and temp gauge. The temp gauge gets it's gnd off of the fuel gauge, but may as well do both if you're in there.