Chrysler Repair: 91 New Yorker: no dome lights,radio, rear defrost, digital ohmmeter, amp fuse

Question
i have no interior lights and no radio , power windows ok,blower motor works, fuses ok inside the car and the ones under the hood, but fuse for rear defrost is out ,40 or 50 amp i belive,

thanks for reading

Answer
Hi Randy,
Yes the 40 amp rear defrost fuse in the power distribution box under the hood also supplies the interior light circuits so you have to trouble shoot that and fuse #12 which is in series with the 40 amp to supply the lights. I would use an ohmmeter to check the resistance that the cold side of the 40 amp fuse socket "looks at" with the rear defrost "on" and  with the fuse #12 in place and a door open, and with the #12 fuse removed, to see if you can get the reading down of the resistance up over 1 ohm (using a digital ohmmeter. If not then the wiring to the defrost is shorted. If so, but the ohms approach 0 with #12 back in and a door open then you have a short to one of the interior light fixtures so you will need to open up each one and pull the bulbs until you find a shorted out bulb/socket as the case may be. The radio also uses fuse #12 to maintain the station presets, so that could be the shorting source, so try unplugging the gray plug in the back of the radio to begin with as it may be the culprit for everything. Let me know what you learn.