THE ACFT WAS 1 OF 3 USED IN A POLITICAL CAMPAIGN IN OKLAHOMA. AFTER LNDG AT MCALESTER, THE PLT WENT WITH THE CAMPAIGN GROUP WHILE THE OTR 2 PLTS STAYED AT THE ARPT & CHECKED THE WX. AFTER THE GROUP RTRND, FLT TO THE NEXT STOP (IDABEL) WASCANCELED DUE TO BAD WX. THE NON-INST RATED PLT ELECTED TO RTRN AT NGT TO ARDMORE, THOUGH HE HAD SAID THE INST PANEL LGTSWERE INOP. HE TRIED TO OBTAIN BATTERIES FOR HIS FLASHLIGHT AT THE ARPT, BUT WAS UNABLE. THE PLT OF N9235Z DID NOT GET ANFAA WX BRIEFING. HE ASKED 1 OF THE OTR PLTS ABOUT THE WX & WAS TOLD IT WAS BAD AT ARDMORE, BUT WAS BETTER TO THE NORTH &NORTHWEST. AFTER TAKEOFF, THE ACFT FLEW NRLY AN HR BFR IT CRASHED NEAR COALGATE. A PERSON, WHO HEARD THE CRASH, SAID THEVIS WAS POOR & THE NGT WAS VERY DARK; ALSO, HE SAID A STORM OCCURRED SHORTLY AFTER THE PLANE FLEW OVER. IMPACT OCCURRED IN A STEEP, NOSE DOWN, INVERTED ATTITUDE. NO PREIMPACT PART FAILURE OR MALFUNCTION OF THE ACFT WAS FND. THE 2055 CST WX AT ARDMORE WAS IN PART: 600' OVC, VIS 7 MI WITH LGT RAIN & FOG. THE ACFT WAS FND ON A FARM ON 2/4/90 BY THE LAND OWNER.