In the back of my feeble mind I seem to remember this symptom occurring on alternator-equipped cars and being solved by putting a diode in series with the idiot light. Can't remember the details though.
The "sometimes" of your problem may have something to do with whether or not your alternator is providing a charge when you shut off the key.
Last edited by Bill Hanlon; 05/24/2023 7:30 PM.
'57 GMC 102, Original 347 V8, HydraMatic, 3.08 rear gear, added A/C, disk front brakes, HEI, AFB carb, '98 Honda Black Currant paint. T-boned and totaled 10/12
'52 GMC 152 Stake Bed, Original 228, SM420, added A/C, HEI, disk front brakes, '67 Chev 3.55 rear gear. Gets used as a real truck.
| 
