I'm trying to get my (new to me) '42 truck's brake lights to function. 6v system. The truck was restored 20+ years ago, and it's wiring was replaced. The new harness accomodates turn signals, and the rear lights are the dual single-filament bulb assemblies. The tail lights work, but the brake lights do not. The turn signal switch is broken. Still learning a lot about these old workhorses. Looking at the wiring, I have a single brown wire feeding the tail lights, with a yellow wire going to the left assy, a green wire going to the right assy, for turns. There is a single brown wire, unterminated, coiled up and hanging from the left assy getting 6v live from the light switch. At the brake switch, I have two black wires that both have continuity to ground (disconnected from the switch). And the brake switch is good. I first assumed the switch was simply switching ground, but the diagrams I found show power coming from the light switch to the brake switch. I defintely feel I'm missing something....likely something simple.
Can anyone shed some light on this? (pun intended).
You should find that the wire coming off the brake light switch that is hot when brakes are applied will go to the turn signal switch. Then if turn signal is on only one side has brake light and the other has turn. If your turn signals don’t work I would start there.
The wire that is energized by your stop light switch would go directly to your stop lights (filaments) if you did not have turn signals. To allow you to have a signal on one side while the stop light stays lit on the other side, the aforementioned wire is routed back to your turn signal switch so it can handle the issue for you. This type signal switch will typically have 7 wires. They will often have an inline fuse holder. A turn signal switch with 5 wires requires lamps separate from your tail/stop on the rear and does not route through the stop light switch.
I'm with Dennis, start with your turn signals and check your bulbs. I believe they should be # 1154 for tail/stop.
Mike
Many Miles of Happy Motoring
3469 Posts on Old VCCA Chat
What I found was one of the brake switch wires is indeed hot....well, more like luke warm.... read .97v with lights on. Checked at the turn signal switch (which is falling apart) and found the same voltage at the yellow, blue and brown wires. Also noted, the flasher relay is missing, so adding that to my list too.
And all bulbs are brand new 6v, single contact, as are the tail lamp sockets. 7-wire turn signal switch.
Depending on the room you have in your tail light housing you can make your tail and brake lights much brighter. If you have the rectangle housing you can modify as I show below. Use a #81 bulb for the tail light (double the candle power of the stock #63) and use an #1129 for the brake/turn signal bulb. You may have to put a slight bend in the bracket as shown below to clear the lens since the 1129 is a larger bulb. Also paint the inside of the housings gloss white to reflect more light through the lenses. Also use plastic lenses. They let more light through than the glass lenses. The pictures below are of a car housing. The truck housing has a flat back but the process should be the same.
7046 old site posts
Save a life, adopt a senior shelter pet
1938 Master Business Coupe
1953 210 Sedan
There is also an LED light option available. They are a huge improvement! I believe The Filling Station and some of the other parts vendors sell them? After almost being rear ended twice in my ‘37, despite functioning lights, I bit the bullet and made the change.
EDIT: oops!… looks like these LED lights are available only for 12volt systems.🥴
@tiny This is what I currently have..... 81's in both tail and stop lamp sockets. Nice and bright.
Now just to sort out the low voltage issue on the brake lamp circuit....
The stock wiring has both bulbs on when braking (at least that's how my 38 is wired) which gives you 12cp of light with brakes applied. If you do the 1129 conversion, that jumps to 27cp. A significant increase. I suspect the low voltage is due to a bad connection. 6v systems are dependent on clean connections. Also, painting the inside gloss white makes a noticeable difference.
7046 old site posts
Save a life, adopt a senior shelter pet
1938 Master Business Coupe
1953 210 Sedan
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