Hi everyone,
New to the forum and need some advice. I have a 1965 F250, 352ci, Custom Cab, nearly all stock and original. The issue is with the driver's side tail light. The running light works, however the turn signal, brake light and hazard do not work on that single light. (Bulb has been replaced). All others lights, front and rear work fine. Is this most likely a problem with the turn signal switch in the steering column or should I look to other solutions first? Thx....

 

The brakes and turn signals share the same wire and bulb filament. Tail lights are on a separate wire and circuit. The two wires run to the housing. The ground comes from the housing being grounded to the bed itself.


Do you have a multimeter? I start by laying a long piece of wire out the length of the truck from the negative post of the battery to near the rear taillight housing and check that I get a very low reading, essentially zero ohms, between the end of that wire and the housing with the meter. There is often a continuity setting on a multimeter that gives a beep if it gets very close to 0 (zero) ohms and the display shows the actual number. I use a spring clamp to hold the wire to the negative post. A larger binder clip should work fine for this purpose, too.


Since your running lights do work I'd think you've got a ground, but this check can eliminate a weak ground. Weird things can happen if things aren't grounded 100%. The lighter, finer bulb filament can be fine because it doesn't draw as much but the heavier filament can fail because not enough juice can flow to illuminate it, for example.


Next, you can set the multimeter to Volts DC and start probing the socket and wiring connectors at the base of the steering column for readings on the wire that runs the brakes and taillights. If you've got no readings coming off the connector at the base of the column then I'd suspect the turn signal switch like you.


If I got a good reading at the base of the column then I'd trace it toward the rear from there. The connector at the housing itself could be corroded inside. They aren't always the most waterproof/dustproof of connectors out there.


I've often used a heat gun (hair dryers work, too) - gently - to warm the rubber connectors - works especially well during cold weather. Once it is warmed a bit they pull apart a LOT easier and won't stress the connectors as much. I've found dust built up inside the connectors, corrosion, all sorts of badness. Typically cleaning the connectors with a brass bristle brush and blowing out with compressed air can help a lot with that.


There's other things you can do with the multimeter - same wire you used for the negative continuity check - use it to check continuity/ohms between the wire at the base of the column and the particular socket connector in the taillight housing. Again looking for very close to 0.00 ohms.


.

 

Thanks TA,
Will start in on those trouble shooting recommendations.....

 

Just a quick follow up.....yes, the issue was a weak ground. Rectified and all's good.

 

If I have not already done so, Welcome to FTE!!

Considering the age of the wiring, tracing electrical gremlins can be a major pain in the backside, suggest purchasing a wiring manual, majority of the Ford part supplier's carry them, if more than $10 suggest purchasing from the source, Jim Osborn Reproduction Inc., for $7 plus shipping.

See where the problem has been resolved so decided to edit out the electrical circuit diagrams.

Again, welcome to FTE, looking forward to your input!!

 

Thanks Dave, great to be here.

Have a feeling I will be asking more questions than being able to give answers, but will help when I can!

 

To piggy back this question. One side of my rear running lights on my 66 f250 is not working. I've just become aware of this. Brakes and turn signals both working.