WARNING: This is going to be long because I want to be thorough enough that if someone decides to respond (hello krosati FORDBOYpete and banjopicker66? - you guys ROCK!), I want them to have good info.
I have a brake light/turn light problem with my 1966 SWB F-100
My signal lights worked, but brake lights didn't. I jumped around the stock harness (because nothing I tried worked) by sending a separate source of voltage to the yellow and green wires at the back of the truck. Now my brake lights work, but when I turn on a signal (left or right), both signals weakly flash in the back (everything's fine up front) like I have an emergency flasher (which I do not).

Now let me tell you how I got here: years back, I went to a PB setup from a '78 250. The 66 brake switch had to go because of the new M/C and I replaced it with a later model switch that I mounted to the brake pedal and fabbed up a striker plate on the steering column so it would work properly. Then I simply took some bullet connectors and ran the old wires to the new switch, and it worked - brake lights, signal lights.
Here's where it gets tricky...I haven't fooled with the truck in a looong time, just puttering around town because it's not a daily driver and not paying attention to what worked and what didn't. I decided to start messing with it again, and discovered while the turn signals worked fine, the brake lights didn't and that the wires were not hooked up to the "new" switch. Hooking them back up did not fix anything, so I started tinkering. After getting a wiring diagram and chasing the dog out of some wires to no avail, I decided just to splice another source of power to the harness through the brake light switch so I would have brake lights. Now I have brake lights and haunted turn signals. I thought I'd stop here and get some outside help before I got in any deeper.

Essentially, I have the original power source (red wire no tracer) to the switch, then off the other side I jump around the harness to the back of the truck with a single wire and splice into the yellow and green wires going to the light assemblies, and now I'm stuck like a pig under a barn door! Any help would be appreciated. A phone call may help 800-728-3246 8-5 CST

 

The bypass you are running from the hot wire to the green and yellow wires is your problem. Don't do that. The original wiring for the flashers uns from the fuse box to the flasher unit to a junction on the engine fire-wall, where one set of wires goes to the front signals, and the other set to the rear. If you have to run new wires, trace the old ones to that junction, and splice in there. While you have the wires stripped at the junction, check them with a test light, while turning your flashers on and off.

Your brake light switch probably has a grounding problem. I would recommend running a new ground wire all the way from the rear light assemblies to the engine block. A good ground will cure 99% of all "bleedover" problems. I'm not an electrical engineer, but what often seems to happen is that lights with poor grounds will try to ground back through an unused hot wire, in your case, the turn signals are probably finding a quick ground through your brake light switch.

However, If the wiring at the back of the truck is untouched, I would leave it that way. Don't try to change it. There are a variety of combinations that will appear to work for individual functions, but screw up when used in combination with other signals.

There is probably nothing wrong with using an independent voltage source for the brake light switch, but running an indendent wire from the switch to the brake lights is gonna be troublesome, because you have the same light back there for the turn signal and brake light (at least I think you do, mine was that way). If you did run a new wire from the brake switch to the rear lights, I know that would cause problems. The brake light would then over-ride the turn signal, and you would be grounding the lights improperly. Unfortunately, I can't remember where the brake light wire is supposed to go, though I could go look at my truck tomorrow and tell you.

Hope this was some help. The fact that you say your turn signals worked fine before hooking up the new brake switch is the clue that that is where the problem lies.

-Luke

 

Luke, thanks for replying. I think it's going to help.

I felt like the new bypass was my problem, too. Just seemed too rigged up to work right. I have a few comments/questions for your well-thought out response:
(1)I have 2 flashers in this truck because I went to P/S with a '73 column and needed an extra flasher to match the harness coming out of the column. The original '66 wire that runs from the original '66 flasher unit to the brake switch is orange with a yellow tracer, no? If I can find that wire (or where it has maybe been re-routed due to the new flasher) I might hook that up to the other side of my new switch, eliminate my jumper, and have lights. I may try that next. Whaddaya think?
(2)If I go to the junction and find no voltage on the cab side with key on and flashers flashing, what should I look for then? A problem under the dash? (yuck) - I think my flashers have to be good because my signals worked before and front ones still do.
(3)How would my brake switch have a grounding problem and how would I check and therefore know that? It's a basic black plastic open/close circuit unit with the two prongs on the end. I think I will leave the back of the truck well enough alone for now (I'm going to remove this jumper) - it does have a trailer harness wired into it, but everything there is good - brown to brown, green to green, yellow to yellow, white to frame. The grounds back there surely are good because when I had the light assemblies out, I used my cordless drill with a wire brush attachment to thoroughly clean them along with the mounting tabs on the bed down to bare metal. In my mind, that has to be a good ground, no?
(4)In your last paragraph, I think you're dead-on. The voltage source is irrelevant to the switch - the jumper's my new problem, and I am going to get rid of it. A new can of unecessary worms.
(5)About my old can of worms...if I go back to square one - no jumper, good turn signals, no brake switch hooked up and therefore no brake lights, where should I start? Junction box? Look for the orange wire yellow tracer on one of the flashers and send that to the switch? (I want someone to confirm that. I got an 11x14 animated diagram from ClassicCarWiring.com and that's what it shows.)

Gosh, Luke, thanks for the killer reply. I'm gonna hunt this dog 'til I tree a coon if it's the death of me! I may be back with more questions, and I'll be looking for replies should they come.

--Jason

 

The brake lights run through the turn signal switch in the steering column - when the stalk is centered everything is connected together so the brake lights light up, but when you use the turn signals one side of the brake lights is disconneced and run through the flasher circuit instead. When you ran the brake light bypass you tied both sides together and bypassed the turn signal switch, giving you the gremlins.

If you have the wiring diagram for the truck check out how the brake lights are wired closely, it's kinda confusing at first how the switch interupts the brake light circuit...

You have two options to fix it - the problem you are having is most likely related to the turn signal switch itself; they are expensive! You'll have to take the steering column apart and go slow to find out where it has an 'open' ( a 'short' would be blowing fuses).

The other option you could take if you don't want to take the column apart is to get one of the adapters used to convert car wiring with separate brake and turn signals to trailer wiring where they are combined like our old trucks, and gerry-rig that into the harness. You can find the adapters for abut $10, a lot cheaper and easier to do than changing out the turn signal switch...

 

Hi Jason,

Luke is dead on the money. . . .

Your brake lights are "separated" out in your T-sig switch up under strg whl @ top of column. Whichever rear lamp the T-sig sends current to is interrupted from the brake light system while T-Sig is operating it. That's why the proper side flashes, or is intermittently interrupted when you put T-Sig on while braking.

When you skirted that separation by looping both lights into a second circuit system, as you say you've done, then the T-Sig switch interprates it as a "cross wired short circuit" rather than a short ot ground, if you catch my drift there.

As Luke pointed out, Brake Lgt & Signal Lgt share same filament in both rear lamps. When you induce current tryies to light all 4 corners @ same time, backwards thru T-Sig switch, which uses flasher ground as T-Sig system ground. That only works with 1 source of current, but you have 2 sources, the OEM source to sig switch [under strg wheel] & ancillary/ extra source you installed to run Brake lamps, outside & beyond the internal system in T-Sig switch.

What you want to do [regardless of switch type, or location] is use brake light switch, when engaged/ on, as supply of current to brake light, current, supply wire, of T-Sig Switch like it was OEM.
It should work correctly.

You can use a pressure activated switch in P/D/B or P/B Sys by getting correct Weatherhead fitting & incorporating it in line. Or you can do it as you already have, just don't cross wire it as you did. Hope this helps understand it. PS: Wait until you hang a 79 Tilt Column in there with 4 way Flashers etc etc. That's a job! FBp

 

John C.,

Thanks for the tip on the switch interrupting the signal. That's a clue for the head scratching yet to come that I didn't know. You're right, the diagram I have doesn't necessarily illustrate that (and I don't know how it would - just something one needs to know and now I do!) BTW, I like your 64. Where'd you get that booster and what in the sam hill is that canister in front of your alternator? Looks interesting.

Fbp,

You got me thinking as well, so....
Back to point (5) of my second post: FBp, you say that what I want to do is, and I quote, "...[regardless of switch type, or location] is use brake light switch, when engaged/ on, as supply of current to brake light, current, supply wire, of T-Sig Switch like it was OEM...." I agree 100% - jumper's gone like Elvis. Here's the deal now (I think):
I have to get the switch hooked up and hooked up right before I can determine my turn signal switch is bad, correct? (although John C. may be right and that may very well be the case because the lights and sigs DID work at one point with the current setup - TBD). That has to be the first step because I may have had the brake switch wired wrong before I screwed the pooch with that jumper (lotta wires under there to mess with and it had been a long time - who knows if I had it right the other day pre-jumper?). I have to get that right, no? As I see it, I have a red wire no tracer on one side providing voltage, and the orange wire with the yellow tracer going into the OEM harness. There should be a connection for that, eh? Does that sound right? I feel I need to have that brake switch snockered before I move on, so I want to cover that.

Thanks fellas!

Jason

 

By the way, FBp (or anybody else),

What was the earliest year FoMoCo put tilts in effys? I have an eye towards a tilt and would like to avoid the 4-way flasher wiring love fest. I'm going to go boneyard hunting and want to ask the right question. Maybe I should open a new thread...j

 

Thanks Jason!

The booster was part of a power front-disk brake conversion from Master Power Brakes. The pump next to it is a vacuum pump for the booster, the cam is too rowdy to create enough vacuum to run the booster... I have donor info on most of the rest of the parts, but I don't know what they used for the booster. There is an adapter that comes in the kit to go between the firewall and the booster anyway, it's not a bolt-on per se. You can save money by sourcing the parts yourself instead of buying a kit, but since I work and do the college thing full time I didn't have time to run all over creation looking for them. The conversion is a lot easier on your I-beam truck.

Summit Racing sells the canister I'm using as a radiator overflow tank (in front of the alternator in the picture), you can get them in all different colors. It's really just an optical illusion from the camera angle I was at - it's not as huge as it looks in the picture.

Back to your problem: there are 7 wires running in and out of the turn signal switch: (1) feeding power from the brake light switch, (1) feeding power from the turn signal flasher, (2) running back out to the front turn signals (one each side), (2) running back out to the rear turn/brake signals (again, one each side), and one running from the the horn relay to the horn button. It shouldn't be hard to figure out which two are feeding power into the switch and which one works the horn; the other four will be a bit tougher to to trace and determine exactly what is wrong. If your wiring diagram is color-coded it will make your life a lot easier, if not I'd suggest pulling the steering wheel (you'll have to do it anyway if the switch is toast) to check the colors out.

If you have the wheel off and can see the switch cam, the two wires in the center of the switch cam are the power feeds, the outside ones are the signal lamps. The top connector on one side of the switch, and the bottom connector on the other side will be for both signals on one side of the truck. when you work the switch you can see how one of the brake lights is disconnected and fed power from the flasher instead of the brake switch when the cam moves.... the problem should be a lot easier to figure out if you can look at what the switch is doing as you take voltage readings. You may be able to get by with just cleaning up the terminals a bit - all they are is a piece of stiff wire striking a brass tack!

 

I spent some quality time troubleshooting the signals on my '57 panel truck recently. Some of the problems I found:
- corroded fuses (solved by sanding fuse ends and holder clips).
- corroded connections (solved by replacing bullet connectors, or cleaning and tightening old connectors
- body of lamp did not ground to chassis: solved by sanding under mounting bolt, and replacing rusty corroded lockwasher with new one
- intermittent turn signal switch: solved by squirting contact cleaner into switch and working it back and forth a bunch of times. This required a puller to get the steering wheel off...

 

Grandaddy always told me to check the simple stuff first!
I've done all except the contact cleaner.
I'm still waiting for an answer on the orange wire with the yellow tracer question. Jumper's gone already, no spooks in the sigs

 

Man, what a great response. It may take me awhile to read it all!
I too had some problems with my turn signals and finally traced the problem to the signal switch. The two rods were worn to the point that they would not make contact when I engaged the drivers turn signal and the brake lights worked when they wanted to. I ended up buying a replacement part for a 67-? truck and grinding off the rivet holding the top on, attaching the wires and drilling a hole to accept a self tapping screw with a large head and washer. Never had a problem after that.
Since you replaced the pressure switch on the Mc with a switch at the pedal, your wiring reall shouldn't have changed. All you needed to do was relocate the wire from the MC to your new switch.
My signal lights worked, but brake lights didn't. I jumped around the stock harness (because nothing I tried worked) by sending a separate source of voltage to the yellow and green wires at the back of the truck. Now my brake lights work, but when I turn on a signal (left or right), both signals weakly flash in the back (everything's fine up front) like I have an emergency flasher (which I do not).
By doing this, you are trying to connect two seperate circuits that cannot operate the bulb at the same time. Sort of forcing it to ground the circuit.
Your problem is almost definaly the switch itself, not the wiring.
Another solution: Add custom brake lights in a rollpan under the tailgate and run your brakelights to them and leave the turn signals as stock. Problem solved and a custom touch to boot.

 

Welcome to the party, krosati. It's been fun reading all of the well-thought out and well written posts; of course, I would expect nothing less from a bunch of effy ford boys - you'll find nothing this high-minded on any bowtie board!

You are dead on the money with your paste of my post. That was obviously a mistake on my part - ingenous, but ignorant (sometimes those two go hand-in-hand) and definitely desperate. Everybody's called it, and I can now see the error of my ways. ;-)

I have been given a bunch of ideas on how to fix my haunted lights short of tea leaves and a seance, and the consensus is building that it COULD be my signal switch, which I think may very well be the case. I have just one problem with that, though, and that is I must get my existing brake switch hooked up and hooked up correctly before I go any further. Hell, everything might just WORK if I do that!! The more I crunch this in my head, the more I feel that the switch was hooked up incorrectly the other night before I got desperate and punted by running the podunk jumper. Earlier in the thread, I stated that it's been a looong time since I first did the brake swap and cannot remember the original wiring situation with that new switch or when, why, or how it became disconnected.

True to form, I have been posting and reading (and learning) but not fixing (except for removing the ill-avised jumper), so I haven't had the chance to get under the dash with the wiring diagram and hunt down that orange wire with the yellow tracer.

But I gotta tell anybody who is reading this: This forum is like having hundreds of years of extra experience right in the shop and is a godsend when a deadend crops up. I seriously believe my beloved Grandaddy is out there anonomously posting in this forum from his perch in heaven helping us all out.