Thread: '51 Chevy taillight wiring

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brake light switch is brand new, and I have brake lights on the right side.

Is it possible that this car was really designed to use 1 stop light? DOT provisions before january 1952 allow vehicles to have 1 stop light, and I know not all GM trucks before that time got 2 taillights.. I'v got good grounds, solid connections both sides and it just doesn't make sense. It's wired correctly. ither the turn switch is malfunctioning or it's only supposed to have 1 brake light.

You really can't tell without a schematic of the turn signal switch internals, seems to me. However, on your schematic you have a "natural" color wire going from "connector on stop lamp switch wire" to the lower connection on the turn signal switch, which would seem to be a +6V when you actuate the brake switch, and that lower connection has "existing jumper" to the top connection on the turn signal switch. Logic would say that this powers both "legs" of the turn signal switch when braking. What I don't understand from your schematic is that it only shows one wire to each of the rear lamps, "natural with black & green cross tracer". You need two wires to each for separate tail light and stop light filaments. It appears to me that this schematic only shows your parking & tail light circuits, and that there must have been a second schematic for your rear stop/turn circuits.

If you compare your wires on the turn signal switch to the schematic you've shown do they match, or do you have two wires to the rear that are not shown on the schematic? You either need a helper to press the brake and energize that circuit so you can check for voltage at the turn signal switch, or a right sized stick to wedge between the seat back & the brake pedal to keep it pressed down tight enough to set your pressure switch. As an alternate you could jumper from your battery + to the switched lead on the pressure switch, and continue to work alone (often my approach).

IMHO, it's easier to pull the bulbs in the tail lights and put the turn signal in either socket and check for voltage.

I do have a seperate feed for the tail/ parking lights, and each socket for the tails has 2 wires/ twin filliment 1154 bulbs. The turn signals did not come standard in '51 and this is the dealer installed Guide 6004 switch, so the '51 Chevy diagram itself, shows no turn switch and the brake lights are just connected to a main feed from the brake switch in that diagram. The turn signal diagram is more of a suppliment to the main diagram for cars with turns, and is probably the schematic used when they were installed. exactly what I have down to the pinout on the back of the switch, except the feed for parking/ taillights which is not shown on the turn diagram. I can jumper the pressure switch pretty easy with a test lead

OK, so the schematic is only for the turn/stop circuit, which is the brighter of the two filaments. In that case the "existing jumper" appears to be to feed both sides when the brake circuit energizes, IMHO.

Originally Posted by NTFDAY

IMHO, it's easier to pull the bulbs in the tail lights and put the turn signal in either socket and check for voltage.

I get good voltage both sides doing this.

Originally Posted by Matt167

I get good voltage both sides doing this.

Where the "existing jumper" is shown on the schematic can you hook a jumper wire between those points and see if it gives you both brake lights?

Originally Posted by rspears

OK, so the schematic is only for the turn/stop circuit, which is the brighter of the two filaments. In that case the "existing jumper" appears to be to feed both sides when the brake circuit energizes, IMHO.

Your right, it does. didn't look that close before. The backside of the switch has soldered connections and is not very assessable. can I make the repair outside of the switch? as in jumper from the brake light switch to the LH turn/stop wire?

The bright filliment is for the brake lights

Originally Posted by rspears

Where the "existing jumper" is shown on the schematic can you hook a jumper wire between those points and see if it gives you both brake lights?

The switch has soldered connections and it's not easy getting to the back side of the switch itself..

The voltage will fluctuate between 0 and 6 volts depending on which side you have actuated .

That's what I'm getting thru the sockets on both tails with the turn circuit working. reading just about exactly battery voltage on and off like it should.

Originally Posted by NTFDAY

The voltage will fluctuate between 0 and 6 volts depending on which side you have actuated .

Ken,
I agree for turns, but that jumper is the brake circuit which appears to jumper both sides together. If so, then when he jumpers power to the brake switch lead then the bright filaments in both sides should light. What I cannot figure out, without an internal schematic of that turn signal unit, is the case where you press the brake, and at the same time have one turn signal "on", in which case both rear lamps should be "bright", with one flashing for turn. I don't see how that is accomplished with this switch.

I don't see how it would work like that ither, unless it was not taken into account given turn signals were still pretty new.. I think I can jumper the stop switch with a diode so it doesn't back feed and get around the broken jumper in the switch. I may have to pull the switch apart again, which is a pain.

"can I make the repair outside of the switch? as in jumper from the brake light switch to the LH turn/stop wire?"

No you will lose the turn signal function for the left side and end up with brake light only. It sounds like the switch is toast.

Does your switch look like the one pictured in the drawing, if so there is a very good chance you can just open it up.

Could be just a dirty wiper for the left side. Best suggestion hit it with some contact cleaner, aka tuner cleaner.


This guy shows a very similar wiring layout as you posted.

Universal Turn Signal Switch | 7-wire unit for vehicles with combination stop and turn signal lamps requiring brake light circuit.

BTW the only thing that makes the switch/unit 12v or 6v is the flasher.

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"you press the brake, and at the same time have one turn signal "on", in which case both rear lamps should be "bright", with one flashing for turn. I don't see how that is accomplished with this switch.''

* With RH turn selected; the switch opens the brake switch voltage path to the RH bulb. At the same time it creates a new path for the flasher voltage out the to the bulb. Think of it as a double poll single throw switch.

This is why only a turn flashing signal is seen out back when the break has been applied.