Dashboard warning lights?

My car runs okay. It used to be very intermittent but now it seems often. It appears that when I turn on headlights or windshield wipers (it has daytime running lights) that the dashboard lights go on and all of a sudden, I lose fuel gauge, temperature gauge and my speedometer--by losing they go to empty, no temperature & zero on speedometer. Sometimes all the LH lights come on--Brake, Check Gauges, Theft system, Airbag and service light. On my RH side I have a continuous Check engine light, ABS and just recently an intermittent Coolant light. I have had codes scanned with dash warning lights on. Check engine light is something with catalytic converter. ABS light--I have bought 2-left Engine removal procedures right wheel speed sensors with new wiring harness and just awaiting when my mechanic friend has time to help me. A couple days before Christmas some of the LH dash lights came on and I immediately went to an auto parts store to check the codes--The person said that a "coolant sensor relay?" showed up. I did have my car overheat (stuck in traffic line) maybe 2-3 months back. At that time I let it cool and added coolant Engine removal procedures the only thing that happened was very occasionally the RH coolant light came on but disappeared quickly (I have been checking it on a regular basis)--I don't know if that incident caused the coolant sensor relay to crap out.
Either way both the sensors I listed above will be corrected ASAP. In talking with people some say it may be a short or grounding problem.I know absolutely nothing on how to check and fix. It is very cold in the mid-west, I am not allowed to do work on my car due to the lease and my friend just recently moved and I do not think he has a heater / salamander. Also, he works for a municipal street division and has been on 12 on-12 off snow removal duty. I don't like having to buy parts all the time until what car situation is taken care of along with being an elder on a fairly low fixed monthly income. I am willing to buy the coolant sensor relay if need be, as I already have bought the wheel sensors. Also many years ago I had a Datsun P/U and it had an EGR? That just counted how many times the engine had been started for servicing purposes. Back then all I had to do is pull a rubber plug out & take a paperclip and press to reset it. I am not sure if my vehicle has something like that--I've googled it without much success for info. Besides taking of battery cables to attempt to clear computer and gauge diagnostics I do not know how to clear the computer memory to go back to factory reset. I really try to stay on top of maintenance of my car to minimize other problems. I would really appreciate any advice to correct my car problems and where to start.
Thank you!