Electrical problem
1990 Mercury Marquis V8 Two Wheel Drive Automatic 110000 miles

Trying to determine if there is an cause I haven't checked>
Initial Symptoms: Sudden loss of all electricals except interior lights and horn. Wiggled the battery terminals (found to be a bit loose) not change. Waited a few minutes fired up with one more mishap on my way home.

Next day, power available (dash lights), but would ebb away within a 10-15 seconds. Swapped for known good battery,swapped main battery cables for known good ones. Checked every fusible link listed in the owners manual and ever fuse in the fuseblock. Also tested a ECM, Fuel Pump, & A/C relays & diode No luck.

Next check, same ebb of power. Swapped ignition switch. Started and ebbed a few times, then nothing. Swapped switch back to original without change.

I get power to the ignition switch when off, but it disappears when the switched to any on position. I haven't found any broken or damaged wires. Engine will crank if solenoid is jumpered. No power to do a ECU test.

Any ideas?

Hi pdubu,

Thank you for the donation.

The symptoms described are most probably due to a bad connection. I would suspect one of the main harness connector from the battery to the ignition is bad.

Check for burnt connectors at junction or fuse boxes.