Why does my brake an abs light come on a nd my tach jumps

stanleyearl55 , check battery connection at both ends for loose/corrosion (maybe remove and clean, tighten) to be sure, have alternator and battery checked to see if failing/weak and at the same time have vehicle checked for diagnostic codes that may relate to your issues. Some of the auto parts suppliers offer free code reading, battery and alternator testing like Pepboys, Nappa, Advanced auto parts,etc and some of the guys are very knowledgeable and may have seen the issue often and put you on the right track.

Do a wiggle test of wiring harness,especially the one under battery tray. While doing the test with engine running have a 2nd person observing the gauges and dash lights watching for a change. If change is noticed the problem will be in that area. Check wires for damage/loose/corrosion and do necessary repair. If not wanting to diagnose/repair yourself have a good local repair shop have a look diagnose and estimate repair. Good luck. I hope this helped you out, if so let me know by pressing the helpful button.