1967 F100 brake lights & turn signals not working

[hillsa]

I spent about a year getting the wiring harness fixed (that's another story) and sorting out issues with my brake light and turn signal (new FoMoCo) switches. But, for the past year, everything has been working fine.

A couple of weeks ago, I was driving the truck on one of my normal "put some miles on it" during the weekend and noticed that the turn signal indicators weren't working. Well last weekend, I decided that I would see what was wrong and found that I had a 20A fuse blown. So, I got that replaced and figured that everything would be working -- not! I did find that I had voltage (~7V) across the wires going to the flasher when the module was unplugged and the turn signal activated. But, if the module was installed, no voltage. I stopped there because I figured I had a bad flasher and I had too much other stuff going on for me to do any additional troubleshooting

So, this weekend, I picked up a new flasher module and installed it. Still no turn signals and I verified that I didn't have any brake lights either. Again, I have verified that I have voltage (~7V) to the flasher wiring when I engage the turn signal but no voltage when the flasher is installed in the connector.

I have read several threads concerning troubleshooting turn signals but have no idea what wire is supposed to be hot (is it the solid blue wire, #44) and am stumped why there is no voltage across the flasher wiring when the flasher module is installed (or should I be checking for current at that point).

Some guidance would be greatly appreciated.

[fordman]

it should be 12 volts you are looking for. what year is your truck? checking for power into the turn signal switch is the first thing to check for. the brake light wire is what brings power into the switch.

[hillsa]

It's a 1967 with a 1968 chassis harness (part of the long story from 2009 thru 2010). I just double checked and have 5 volts (I put the multimeter on the proper scale this time) across the two terminals of the turn signal flasher socket (without the flasher module installed) when the turn signal is activated. I also have 5V across the brake switch socket.

Before I pull the steering wheel off again (I had it off yesterday trying to troubleshoot this problem), what wires do I need to check for voltage across (green w/white stripe, white w/blue stripe, or ...)?

[hillsa]

Just pulled the steering wheel and checked for voltage across the wires on top of the turn signal switch, blue (#44) and green (#282). Depending on which scale I select for my multimeter, I read either 5V or 7V. My multimeter is at the bottom end of the price range of Radio Shack's models, so I don't put a lot of credence in the actual measurement, but I do have voltage at the TSS.

Also, I pulled the TSS out of the column and checked the voltage from the blue wire (#44) on top to any of the four wires on the bottom of the switch. When the turn signal is not activated, there is voltage -- ~7V. When the turn signal is activated, I have no voltage across any of the wires. I would have assumed that current would flow through one side of the circuit but the other side would continue to show a voltage.

Have I mentioned that I hate troubleshooting electrical issues?

[fordman]

warning. this diagram is for dummy lights in the instrument cluster and all wires on a full gauge instrument panel truck may not be the same. http://www.fordification.com/tech/wiring/68-23.jpg

wire number 44 is blue. it is the wire that comes out of the turn signal switch and goes to the flasher can on the drivers side of the instrument cluster. wire 810 is the brake feed wire going up into the turn signal switch. following the diagram posted. the brake light switch ends up going through the emergency flasher and then to the flasher switch. for no brake lights try replacing the brake light switch. it should have no power when closed on one side. and power to both sides when opened (the pedal applied). when checking any fuses make sure both sides of the fuses have power on both sides. if not the fuse is bad or the terminal on the fuse is bad.

[Thunderfoot]

When your are checking voltages with your meter you need to connect the black/ground/negative lead to a good metal part of the truck for ground and then use the red/positive lead to measure the voltages at your points of interest. The way you are trying measure in line you will not get correct readings ( I wont go into details on that )

The Blue wire should not have any power on it once the flasher is removed, with the flasher installed it should have full 12V. If you remove the flasher then the plug should have full 12V on the orange/yellow striped wire side of the plug.

On your issue do the lights come on at all?
Also, try replacing the emergency flasher to see if that helps...

[hillsa]

I've found some time and am back on this troubleshooting effort.

Two things that I have checked today are that I do have voltage at the brake light switch. But, if I jumper across the connector (trying to determine if it is a bad switch) then I still don't have brake lights. So, I moved up to the turn signal harness connector. I have verified that I have 12V across both the blue wire and the blue/yellow stripe wire. But, I do not have any voltage on any other wire in that harness. Also, the results are the same whether the brake is applied or not.

So, is the consensus that I have a bad TSS?

If so, it's a little disappointing since this was a FoMoCo part that I installed about a year or year and a half ago.

[fordman]

if it is a bad tss. remember that nos parts are almost as old as the truck. and not always the best old plastic. new plastic is better. take the wheel off and press on the tss cam to see if the lights work when you press on it. if it works then that is the problem.

[Thunderfoot]

If you didn't have any power on the Green/red striped wire on the TSS side or the Red/black striped wire on the harness side for brake lights, with the brakes applied, I would look into that problem first... As you originally blew a fuse I would suspect that this Red/black striped wire has had a problem somewhere (shorted) and now it is also affecting the turn signals as it is shorted out. I'm just guessing but it is possible that it shorted and then broke away leaving the incoming power side free and the other side going to the TSS still shorted...

Also, did you try replacing (or unplugging) the Emergency Flasher??? if it shorted internally it could cause the same issue.

[hillsa]

First, let me say that I appreciate all the help. Second, I'm still at the same place I was at the beginning of this weekend.

Let me see if I can summarize where I'm at:
1. Replaced 9A fuse a few of weekends ago
2. Replaced flasher (both my emergency and turn signal flashers are wired together from PO)
3. Steering wheel is off & half the connector for the turn signal switch harness
4. I have voltage on the red wire (#284) to the brake switch when the brake is not applied (no voltage otherwise)
5. No voltage on the red/black wire (#810) to the brake switch
6. Jumper across red wire (#284) and red/black wire (#810) and still no brake lights
7. I have voltage on the blue wire (#44) at the turn TSS harness when the brake is not applied (no voltage otherwise)
8. I have voltage on the blue wire (#44) at the turn TSS/cancel cam when the brake is not applied (no voltage otherwise)
9. I have voltage on the blue/yellow wire (#482 - horn) at the TSS harness & at the TSS/cancel cam
10. No voltage on any other wire at the TSS harness
11. Dome light and dash lights work.
12. Headlights & taillights work.
13. Windshield wipers work.
14. Heater fan works.
15. Truck cranks & runs.

My understanding of the wiring diagram has power coming from the blue/white wire (#40) from the fuse block to the flasher where the red wire (#284) is connected to it. So, by my reasoning, the red wire (#284) should be hot at the brake switch and the red/black wire (#810) should only be hot once the brake is applied to complete the circuit. If that is correct, then what I'm showing in #4 & #5 above should be proper behavior. Correct?

Suggestions?

[fordman]

2 needs to be put back to two flashers instead of one. this also shows soemone was havign problems before you and didnt know how to fix it.
4-8. is a possible brake light switch gone bad.
9 is a ground not a power wire. so that is wired wrong.

[67shorty]

I'm having the same issues with mine too, no brakes lights, no flashers , no turn signals and I do have tail lights and back up lights...please let me know if you figure it out.