Topic: 1948 Ford (convertible) Lighting Circuit Mystery


oosterhousek@gmail.com    -- 06-18-2022 @ 5:00 PM
  Headlights work. No other lights - no dash lights, parking lights, tail lights or brake lights. Traced the wiring diagram and took the multimeter out. Power to both battery contacts on the light switch, but no power except for the headlight out, so I assumed the problem had to be the switch. Just replaced the switch (that wasn’t very fun trying to find the elusive release button) and still no other lights.

The circuit breakers under the dash (just above the instruments) show power on both sides. There is a circuit breaker (I think). on the firewall right next to the power top switch, that isn’t showing power from either post, but that doesn’t seem connected to that circuit and the power top works, as does the other dash items - gauges all work, radio, lighter, etc.

What am I missing?


trjford8    -- 06-19-2022 @ 7:16 AM
  Check all the grounds to the parking lights , tail lights and dash lights Grounding is critical in these old Fords especially in the 42-48 cars.. Also check the power to the brake switch. There should be a constant hot to one side of the switch and when the pedal is depressed the other side of the switch should also show power. If you have power to both sides then it has to be grounding. You can run extra ground wires from the tail lamp housings to a clean place on the frame to see if it's a ground problem.


TomO    -- 06-19-2022 @ 9:32 AM
  The online wiring diagram is incorrect for a 1948 car and has serious errors, like a black wire changing to green without going through a connector.

It shows that all of the lights that you are concerned about go through the left side of the circuit breaker. Do you have battery voltage at all 3 light circuit breaker terminals?

Tom


Tooster    -- 06-20-2022 @ 8:43 AM
  I need some help understanding the “left side of the circuit breaker”. Under the backside of the dash, above the instruments there are two blocks (each with two posts). There is another breaker on the firewall near the power top switch.

Under the dash, with the power running, all four posts on the two circuit breakers show power. When I put the headlights on (which work), the post nearest the passenger side doesn’t show power.

On the light switch, the two power in posts show power all the time and the headlight posts shows power when turned on (obviously, since the lights work). On the other side of the light switch (left side), the power in post shows power, but the other tow “out posts” don’t show power no matter what position the switch is in. Note, this was the same as the original switch.




TomO    -- 06-21-2022 @ 8:03 AM
  From your description of the voltages at the circuit breaker, it sounds like one of your circuit breakers has corroded contacts. I don't know if a good replacement is available, if one is I would replace it.

If a good replacement is not available, I would remove the circuit breaker and clean the contacts with a 800 or finer sand paper.

I don't have a wiring diagram that fits your description of what is in your car. If you have a 1948 Operators Manual, it may have a correct wiring diagram.

Tom


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