Dash light issues

A

AD1948Ford

Senior Member
To start, I have a 1948 Ford Tudor Sedan. The dash lights work but something weird is occurring. When I have the key in the vertical position (off) and pull the light switch out, all dash lights light up like they are suppose to. When I turn the key to the right (coil wire and accessories become hot), the speedometer and clock lights stay illuminated but the lights on the other 4 gauges (fuel, temp, amp, oil) turn off.

Any ideas on what could be causing this?


Best,
Aaron
 
That is interesting. Assuming you have stock wiring, the diagram in the 1939 to 1948 Service Manual shows that the ignition switch has nothing to do with the dash lights. The ignition switch is fed off the circuit breaker by a yellow/black wire. From the switch, a black/red wire goes to the ignition resistor, and a black/green goes to power the instruments.


A red/yellow wire goes from the center terminal of the circuit breaker to power the headlight switch. A black wire goes from the other terminal on the same side of the light switch and splits in two, with one black going to the license plate light and the other going to the dash light dimmer switch. Two black wires come off the dimmer switch, one black wire powers the two instrument lights and the speedometer light, while the other black wire powers the clock light.


My guess. Something is not wired right, because the diagram shows the instrument and speedo lights are on the same supply from the dimmer switch. Does the dimmer switch work? I had to take mine apart and clean the contact arm and resistor windings. Is there is a bad connection in the bullet connectors?
 
Dimmer switch replaced recently and everything was working fine. Just started acting up now. I’ll check dimmer switch again
 
There's a wire on the wrong terminal on the headlamp switch. It's possible the lights for the gauges are on the terminal for the parking lamps. Dash lights should be wired with the wires for the taillamps. Parking lamps are on a separate post.
 
AD The only light on the dash that the dimmer switch is connected to is for the high beam indicator by a green/white wire. I have attached a wiring diagram, which I hope will be clear enough to use.
 

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Believe you are misreading the wiring diagram. The high beam indicator is not connected to the dimmer and all of the dash lights are connected to the dimmer as is the clock light. There are three dash lights, two labeled Instrument Lights and one labeled Speedometer Light. The Clock light is on a separate circuit from the dimmer.
 
Now I am confused. Maybe I have an incorrect electrical drawing, as mine shows a green/white wire for the high beam indicator coming off the same terminal on the dimmer switch, as does the two green/black wires the go to each of the headlights.
 
51woodie said:
Now I am confused. Maybe I have an incorrect electrical drawing, as mine shows a green/white wire for the high beam indicator coming off the same terminal on the dimmer switch, as does the two green/black wires the go to each of the headlights.
Click to expand...

Ok, now I see the problem (and I was using the diagram you posted), it's the term "dimmer switch". You are referring to the high/low headlight beam switch. I thought we were talking about the dash lighting and the dash light dimmer (rheostat).

Just reread all the reply's, and floor dimmer switch seem to be what is being referenced, :)

But think we are all in agreement, there is a wiring issue somewhere.
 
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Thanks everyone. I’m referring to the dash lights and the dimmer switch on the dash that controls the brightness of these lights. The high/low headlight beam switch and headlights themselves work correctly, as did the dash lights up until yesterday. To everyone’s point, somewhere there is a wiring issue. Given everything was working a few days ago, I will go back to check to make sure I did not accidentally bump something while working under the dash and disconnect a connection somewhere.
 
Its interesting how component descriptions become confused. In England, Australia, NZ etc. we call the floor foot switch for the headlamps the DIPPER or DIP switch because it dips the headlights down or up. The dimmer switch or rheostat is for the instrument lights to make them bright and dull. Having said that some early cars had only one single filament headlight bulb which had a switched resistor in series so that could be DIMMED or it might have a solenoid dipping reflector. Still confused ? Oh well. Regards, Kevin.
 
51Woodie, no luck so far. Everything is wired correctly and the dimmer switch (rheostat) is working properly. Still trying to diagnose the issue
 
When things that aren't supposed to function start to function when a different circuit is powered up, there is a likely possibility of cross shorting. When the switch is in the "ON" position, all other circuits other than individually switched hot all the time circuits will then be powered up. This would be accessories and and ignition.

Lighting, horns, and starter circuits are hot all the time so that the park lamps or even head lamps can be left on with the ignition switch key removed.

I have no idea what the condition of the wiring in your 48 is in but you need to check for a short. Being near the instruments sort of points the finger to the hot wire to them cross shorting to those affected light circuits since they are close together.
 
Is all of the wiring original, as in original Ignition Switch on the column, Light Control Switch, Circuit Breaker Panel, etc?
 
I think they changed to a regular type ignition switch in 1947 or 48. I was still on the column but it's not a flip switch.
 
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The 46-48 wiring diagrams still show the flip switch, but they can be highly stylized and I'm not that familiar with these model year changes. Wondered if there was some none original wire routing contributing to the problem. If the problem started with the change of the dimmer switch I think I would remove it and jumper the wires across to see if the dimmer itself is defective.
 
Good point on the short. Did not think of that. The wiring has been completely replaced with new original wiring harness. The ignition is not a flip switch for my year and model. It’s located in the column mount. I did hook up the radio power wire to the ignition switch so that it would have lower when the car was on but not when the key was off. I also installed the original radio into the car and was working under the dash so I could of easily jossled the harness around and some how created a short. I will give it a good once over tonight or tomorrow.
 
Figured it out. Had a loose ground wire, as well as a connection on the back of the gauges that was loose and was contacting another wire. Fixed both issues and everyone works as it should. Thank you all for the help.
 
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