This is going to be the dumbest thing you read today.   1956 Mercury,  Rebuilt the engine this winter, have taken it out a few times since.   Pulled out of the driveway last night, hit the lever to turn the heat on, and all the lights went out.  Headlights, brake lights, and all interior dash lights. It was after dark so i pulled it back into the garage (it was still running after the lights went out).   So i get under the dash to have a look.  No blown fuses, or bare wires that are obvious.  The heat lever did have a wire that ran to the radio under it, that it could have bumped.   Gave the headlight switch a jiggle, nothing seems loose.   With the key on, not running i hit the wiper switch and the lights came back on??!!   I think there must be a short in something?      NOW-   go to start it and it will not.   Haven't had any problems in the past.  Its cranking, but wont fire.   I pulled plug wire off the coil and held it close, and could see the spark jumping (using a remote starter button). Put that back on and pulled a wire out of the distributor, could see that sparking.  Sprayed some staring fluid in the carb, absolutely nothing.   Could a short on the headlight circuit cause it to not start?   It was running fine after the lights initially went out.   I metered from positive battery post to ground and have 2 meg ohms?     I dont see any fuses for the headlight circuit anywhere either?   All other electronics are still working fine (radio, turn signals, horn, blower, ignition, dome light) but no dash lights, headlights, or tail/ brake lights?     Any help would be appreciated 

Beautiful car! Weird things happening electrically are usually traced to bad grounds. Is your negative cable grounded at the engine? Check and thoroughly clean all ground connections and make sure the engine is connected to the body and frame with good connections. With you engine cranking over well, I would suspect a bad bond of the engine/body. 

Thank you.  I'll check that out tonight.  Also thinking i should pull the headlight switch out and check  it all out.   I know the battery negative goes directly to the engine, and there is a ground cable from body (firewall) to engine, but i don't know if there is a link to the frame.  I'll check and add one.  

from strange past experience pull the battery cables off the battery and clean them even if the battery and connections are NEW.

Vnygra:
I have a '56 Ford and it has a circuit breaker on the back of the headlight switch that breaks the circiut when it gets hot, then turns it back on when the circuit breaker cools down.  If your Mercury has the same set up the circuit breaker might be the reason your lights are going off and later coming back on.  The headlight switch on my Ford supplies power to the headlights, tail lights dash lights, interior light and brake lights, so it seems that the circuit breaker may be causing your lights to go off. HOWEVER, if it is the circuit breaker, then it Is just doing its job and there will be an underlying problem in your wiring. The information from the other posters is very good in my opinion and I would start by checking the ground straps.  There are several grounds wires on my car (and I assume on yours) that could be the culprit.  My Ford has a ground cable from the battery to the engine block.  Make sure this cable is not frayed and both ends are clean and tight. There is also a heavy wire from  the engine near the throttle bellcrank to the firewall, and ground wires from the headlights to a ground on the left inner fender near the voltage regulator.  There is also a junction block on the inner fender that your headlight wires, front parking light and turn signal wires go through. I would pay special attention to the headlight grounds and making sure the junction block connector holes  and the bullet connectors that fit in the holes are clean.  Remember that the wires need not be broken to cause the problem, heat can be generated by poor connections anywhere in your light system.  There is also a junction block on your steering column down near the floor that controls your tail lights, but it is inside the car, protected from the weather and would be about the last place I would suspect.  Please let us know how what success or further problems you have.
Larry




   

Thanks for all the info.   When i got home from work yesterday, i took off a battery disconnect switch that i had recently installed, and the car started fine, but still no lights.  Pulled the headlight switch out.  It had power, but didn't appear to be moving the power to any of the out going terminals.   I put a jumper from the 12v to each of the terminals, and each light would turn on fine.   So the switch must have just gone bad i suppose.  Still doesn't really answer why it wouldn't start the other night though...   There is no fuse or breaker on the switch i have, maybe it just burnt something up internally.   Ordered one that has a fuse spot on the backside.  for now, i installed a jumper from 12vdc to the brake light terminal, so i can try to drive it around this weekend and have brake lights working.  

I had a similar problem like yours with tail and brake lights after replacing everything I had taken off for a repaint. Every thing worked before. There is an inline fuse going to the flasher that was not making good contact. It was an ez fix but caused a lot of frustration.

I purchased a fantastic aid in all this from www.classiccarwiring.com It's 11x17 laminated and in full color. The schematic shows every stock wire for your car with a wire color code. Saved me Unbelievable time and well worth the few dollars it costs.

56 Vic, B'Ville 200 MPH Club Member, So Cal.

Slightly OT, but I’ve have 4 of the shut off switches below fail. Very small amounts of corrosion under the knob where the contact is actually made. I carry a wrench to remove them if necessary. They can be different color knobs, or standard terminal. If that’s what you removed, be aware.

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miker
55 bird, 32 cabrio F code
Kent, WA
Tucson, AZ