R112 wiring questions

If you want to make it easy on yourself and you are not doing a 100 pt. restoration buy an aftermarket turn signal kit of the type used in these old trucks as add - on's. A good one is not all that expensive, you will know that all the internal electrical contacts are working which is usually not the case in an old truck and the fresh color coded wires along with the wiring diagram that comes with it makes for an easy installation. The original column unit in my S truck was a mess. I just cut away the wires, and used the feed to power up the new unit and extended other wires out where needed.

With the switch in the middle position, (no turns signals on) the feed from the brake light switch is connected to the left and right rear feed, when one or the other turn signal is selected, that rear light is disconnected from the brake feed and connected to the flasher feed (along with the front light on the chosen side). The flasher is in series with the lights, and in the center position is not connected to the lights, only connected when a direction is selected on the switch.
It is a complicated switch and only needs to be because the North American mfg chose to use one filament in the rear lights to preform two different functions, turn and stop. European mfg made it much simpler by using separate bulbs for stop and turn. The NA system requires you disconnect and connect the rear bulbs depending on what function you want the bulb to preform at the time.

Thanks Mike. Not doing a full restore but would like to use the stock switch if at all possible. I have a parts truck that has a spare one but it is not wired either. I do have a couple of signal stat aftermarket ones for KB's but would rather not go that route. Thanks though.

Cornbinder,
This is exactly what I needed to know and makes sense. I always wondered how the tailights and brake lights did not conflict using the same filament. Now the challenge is figuring out what wires are what coming out of the harness. I think I need to find the brake light in first and then use an ohmmeter to determine what wires are the output and then from there figure out the blinker out next.

Thanks for your help.

Some states, such as Indiana, began requiring turn signals from the factory on vehicles produced after January 1, 1953. At first the manufacturers sold accessory kits, before they switched to the columns with integral turn signals. [Remember, until turn signals became standard, some manufacturers had only one tail light as standard equipment.]

My KB-1 panel has a single brake-tail light in the middle of one door,
I added signals to it

Cornbinder,
This is exactly what I needed to know and makes sense. I always wondered how the tailights and brake lights did not conflict using the same filament. Now the challenge is figuring out what wires are what coming out of the harness. I think I need to find the brake light in first and then use an ohmmeter to determine what wires are the output and then from there figure out the blinker out next.

Thanks for your help.

The brake and tail light are separate filaments, the brake one being the brighter of the two. The turn and brake share the same filament, so there has to be a mechanical way to separate the two feeds. The turn signal switch is what does that.
Interestingly, Freightliner tractors only had on tail and stop light until somewhere in the 70's. The turn signals were a double faced lamp on the mirror brackets, and met the requirements of the time being visible from both the front and rear of the vehicle. I think they updated the statute in the 70's to require turnsignals to be on the rear of the vehicle, but not sure.
My brother has a boat trailer that only had one taillamp from the 60's and that was also factory.

Don't know what turn signal switch you're using by maybe these will help.

The difficult part is determining which wire from your switch goes where if you don't have them marked by the color coding of the wire. It's a process of elimination. Sounds confusing to read it, but if you mark the wires as you go, this will get you the correct routing. Stock S series switches had six wires. This isn't my workmanship, and I don't know who to attribute it to, but I had saved it years ago, and it's as good as it gets.
_________

All these switches work basically the same, and there's a consistent logic in how the switching is done. You will find different numbers of wires though depending on switch features or design, so that's a good place to start; what wires you may find. First I'm going to number each wire and identify it's function (not all switches will have all wires), then I'll go through how to identify each wire using a continuity meter. If you have a late-model column with 'other' functions on it (cruise, wipers, etc), you need to separate those out. Note that these numbers are entirely arbitrary and unlikely to match however you identify your wires but are merely to show what connects to what when the switch is operated.

The numbers:

1. Brake light power. This wire will come from your brake light switch.
2. Left rear brake/turn.
3. right rear brake/turn.
4. Left front turn.
5. Right front turn.
6. Turn signal power. This wire will come from the turn flasher ('L' terminal on a three wire flasher).
7. Indicator light left.
8. Indicator light right.
9. Horn.
10. Emergency flasher power. This wire will come from the emergency flasher.
11. Indicator light power. This wire will come from the turn flasher ('P' terminal on a three wire flasher).
12. Shift indicator light (some 'automatic' columns).

Identifying the wires.

Now let's get the meat of it. If you have fewer than six wires out of the switch, you have a turn-only switch and it isn't connected to the brake lights. Got six or more? Read the whole post and make sure you do this in the order shown or you can get hopelessly confused. Let's go...

Six wires.

This is your most basic switch. To identify the wires, start with the turns 'off'. You should read continuity between three wires only, and no continuity to/between the others. These are wires 1, 2, and 3 although we don't know which is which yet. Turn the switch to 'left'. One of these three will no longer read to the other two, this is wire 2. Turn the switch to 'right' and 2 now reads to one of the original three, but one won't read to the other two. The one that doesn't read is wire 3. That makes the remaining wire wire 1, or brake light power.

I'll note here that no matter how many wires your switch has, this is the test to find the brake lights. You'll only find one group of three wires with the switch 'off'.

To find the rest of the wires, turn the switch to 'left' again. You'll have continuity between 1 and 3 for brake, and between wire 2 and two of the other wires but not to 1 or 3. These are wires 4 and 6 although we don't know which is which yet. Note these, then turn the switch to 'right'. Now you'll have continuity between 1 and 2 for brake, and 3, 5, and 6 for turn. The one wire with no continuity to anything is wire 4, wire 6 is common to both left and right and is turn signal power, and all the wires are identified.

This is the basic 'identifying test' that is done on any turn switch; any additional wires are simply added functions. In this case, if you want dash indicators for each side, connect those to wires 4 and 5. If you only want a single indicator for both sides, use a three wire flasher and connect the light power wire to the 'P' terminal on the flasher. I'll note here that a three wire flasher is only needed if you're using it to drive a dash indicator light or lights, otherwise a two wire flasher is all that's needed (sized for the lamp load of course).

I'll add here that if you want/need a single dash indicator light but have an aftermarket fuse panel that won't accept a three wire flasher or don't want to add the flasher/wiring, there's a couple of ways to 'cheat' this so it works. If you use a standard 4W incandescent lamp for the indicator, then connect the wires going to the front turns to each side of the lamp (left one side, right the other) without a ground wire. The indicator light will get it's ground through the 'unused' front lamp, but the voltage drop through the small lamp is great enough that the front lamp won't light up or will glow very dimly. This won't work with a LED. As an alternative or if a LED is wanted, you can run a ground to the lamp then install a diode in each wire from the front turns before connecting both to the other side of lamp to prevent feedback into the side not 'on'.

Got more than six wires?

Seven wires.

If you have a seventh wire and have an aftermarket switch with a built-in indicator light, this will connect to the 'P' terminal on a three wire flasher (wire 11). If you have a OEM type switch, this will likely be the horn wire (wire 9). If the horn goes through the switch, you should have a 'brush' that wipes on the steering wheel. This wire should not read to any other wire no matter what position the turn switch is in and if the steering wheel is installed with a working horn ring, should read to ground (the column) when the horn is pressed.

More than Seven?

At this point you're adding features. If you have emergency flashers it will be obvious. You may have separate wires coming off the switch for dash indicators, possibly even separate power for them. To find these, check like this, making sure you check each wire to all others:

If you have two separate dash indicator wires, one of them will likely read continuity to wires 2, 4, 6 when the switch is on left, the other will read to 3, 5, 6 on right. These may read to their respective 'front side' wires of 4 and 5 all the time. If the wire size for 4/5 and 7/8 are the same, either one can be used for the front turn light. If you find a smaller gauge on one, use that for the indicator. If you still have an 'extra' wire and these don't read to the 'side' wires, they may have a separate power feed from the flasher 'P' terminal. Check to see if you have continuity between 7/11 (when 'on' left) and 8/11 (right) and no continuity to any other wires. Separate indicator power is rare on a OEM column, and won't be found if the switch has emergency flashers built in. This will require a three wire flasher if you want to retain this circuit, otherwise you can connect wire 11 to wire 6 and eliminate the need for a three wire flasher.

If you have emergency flashers, when the switch is 'on' you'll have continuity between 2, 3, 4, 5, and 7, 8 (if present) as well as to one more wire, and this wire will be the power wire from the emergency flasher, wire 10. With the flasher 'off', this wire should not read to any other. Make sure this switch is 'off' while doing any prior checks.

You might have a ground wire, but that should read to the metal column parts only, not to any other wires.

If the column was out of a automatic-equipped vehicle, you may have an indicator light for gear position. This wire will connect to the dash lights.

If the checks are done in order, this will identify the wiring on any switch. Do keep in mind though that switches do fail, so if you're using a used column and have issues, it may be the switch. Particularly look at columns that came out of vehicles that have done towing duty or may have had a camper installed; the extra load does shorten switch life.

I'll add that if you're using a three wire flasher, the terminals are marked and must be connected correctly; 'X' is 12V power in, 'L' is load and goes to the turn switch, and 'P' is for indicator lights only.


All these switches work basically the same, and there's a consistent logic in how the switching is done. You will find different numbers of wires though depending on switch features or design, so that's a good place to start; what wires you may find. First I'm going to number each wire and identify it's function (not all switches will have all wires), then I'll go through how to identify each wire using a continuity meter. If you have a late-model column with 'other' functions on it (cruise, wipers, etc), you need to separate those out. Note that these numbers are entirely arbitrary and unlikely to match however you identify your wires but are merely to show what connects to what when the switch is operated.

The numbers:

1. Brake light power. This wire will come from your brake light switch.
2. Left rear brake/turn.
3. right rear brake/turn.
4. Left front turn.
5. Right front turn.
6. Turn signal power. This wire will come from the turn flasher ('L' terminal on a three wire flasher).
7. Indicator light left.
8. Indicator light right.
9. Horn.
10. Emergency flasher power. This wire will come from the emergency flasher.
11. Indicator light power. This wire will come from the turn flasher ('P' terminal on a three wire flasher).
12. Shift indicator light (some 'automatic' columns).

Identifying the wires.

Now let's get the meat of it. If you have fewer than six wires out of the switch, you have a turn-only switch and it isn't connected to the brake lights. Got six or more? Read the whole post and make sure you do this in the order shown or you can get hopelessly confused. Let's go...

Six wires.

This is your most basic switch. To identify the wires, start with the turns 'off'. You should read continuity between three wires only, and no continuity to/between the others. These are wires 1, 2, and 3 although we don't know which is which yet. Turn the switch to 'left'. One of these three will no longer read to the other two, this is wire 2. Turn the switch to 'right' and 2 now reads to one of the original three, but one won't read to the other two. The one that doesn't read is wire 3. That makes the remaining wire wire 1, or brake light power.

I'll note here that no matter how many wires your switch has, this is the test to find the brake lights. You'll only find one group of three wires with the switch 'off'.

To find the rest of the wires, turn the switch to 'left' again. You'll have continuity between 1 and 3 for brake, and between wire 2 and two of the other wires but not to 1 or 3. These are wires 4 and 6 although we don't know which is which yet. Note these, then turn the switch to 'right'. Now you'll have continuity between 1 and 2 for brake, and 3, 5, and 6 for turn. The one wire with no continuity to anything is wire 4, wire 6 is common to both left and right and is turn signal power, and all the wires are identified.

This is the basic 'identifying test' that is done on any turn switch; any additional wires are simply added functions. In this case, if you want dash indicators for each side, connect those to wires 4 and 5. If you only want a single indicator for both sides, use a three wire flasher and connect the light power wire to the 'P' terminal on the flasher. I'll note here that a three wire flasher is only needed if you're using it to drive a dash indicator light or lights, otherwise a two wire flasher is all that's needed (sized for the lamp load of course).

I'll add here that if you want/need a single dash indicator light but have an aftermarket fuse panel that won't accept a three wire flasher or don't want to add the flasher/wiring, there's a couple of ways to 'cheat' this so it works. If you use a standard 4W incandescent lamp for the indicator, then connect the wires going to the front turns to each side of the lamp (left one side, right the other) without a ground wire. The indicator light will get it's ground through the 'unused' front lamp, but the voltage drop through the small lamp is great enough that the front lamp won't light up or will glow very dimly. This won't work with a LED. As an alternative or if a LED is wanted, you can run a ground to the lamp then install a diode in each wire from the front turns before connecting both to the other side of lamp to prevent feedback into the side not 'on'.

Got more than six wires?

Seven wires.

If you have a seventh wire and have an aftermarket switch with a built-in indicator light, this will connect to the 'P' terminal on a three wire flasher (wire 11). If you have a OEM type switch, this will likely be the horn wire (wire 9). If the horn goes through the switch, you should have a 'brush' that wipes on the steering wheel. This wire should not read to any other wire no matter what position the turn switch is in and if the steering wheel is installed with a working horn ring, should read to ground (the column) when the horn is pressed.

More than Seven?

At this point you're adding features. If you have emergency flashers it will be obvious. You may have separate wires coming off the switch for dash indicators, possibly even separate power for them. To find these, check like this, making sure you check each wire to all others:

If you have two separate dash indicator wires, one of them will likely read continuity to wires 2, 4, 6 when the switch is on left, the other will read to 3, 5, 6 on right. These may read to their respective 'front side' wires of 4 and 5 all the time. If the wire size for 4/5 and 7/8 are the same, either one can be used for the front turn light. If you find a smaller gauge on one, use that for the indicator. If you still have an 'extra' wire and these don't read to the 'side' wires, they may have a separate power feed from the flasher 'P' terminal. Check to see if you have continuity between 7/11 (when 'on' left) and 8/11 (right) and no continuity to any other wires. Separate indicator power is rare on a OEM column, and won't be found if the switch has emergency flashers built in. This will require a three wire flasher if you want to retain this circuit, otherwise you can connect wire 11 to wire 6 and eliminate the need for a three wire flasher.

If you have emergency flashers, when the switch is 'on' you'll have continuity between 2, 3, 4, 5, and 7, 8 (if present) as well as to one more wire, and this wire will be the power wire from the emergency flasher, wire 10. With the flasher 'off', this wire should not read to any other. Make sure this switch is 'off' while doing any prior checks.

You might have a ground wire, but that should read to the metal column parts only, not to any other wires.

If the column was out of a automatic-equipped vehicle, you may have an indicator light for gear position. This wire will connect to the dash lights.

If the checks are done in order, this will identify the wiring on any switch. Do keep in mind though that switches do fail, so if you're using a used column and have issues, it may be the switch. Particularly look at columns that came out of vehicles that have done towing duty or may have had a camper installed; the extra load does shorten switch life.

I'll add that if you're using a three wire flasher, the terminals are marked and must be connected correctly; 'X' is 12V power in, 'L' is load and goes to the turn switch, and 'P' is for indicator lights only.

Paul,
I cannot thank you enough as this will likely save me hours of grief. I will give it a go this weekend.

Mike