first post: brake light diagnosis?

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first post: brake light diagnosis?

Post by redstone65 »

Patient: 1965 F100 (inline-6 240) Flareside - daily driver - almost all original except for radiator, alternator, bulbs, fuses, hoses

Current Symptom: brake lights don't work

What started it: Horn was weak and barely audible since I bought the truck. (sounded like a sick duckling)

Steps I took to get from horn not working to brake lights not working:
  1. I had coffee and stared at the wiring diagram and came up with a plan
  2. Once outside, I disconnected wire at the horn and used a length of wire to stretch directly from the positive battery terminal to the connector on the horn.
  3. It sounded great. (Problem must be up-stream)
  4. Reconnected wire to horn.
  5. Removed horn relay from other side of the engine bay.
  6. Cleaned contacts with vinegar and wire brush and reinstalled and tested.
  7. Still barely audible. (Could be horn relay or up-stream problem)
  8. Drove to autoparts store to get a new connectors for the fuel sending unit. Everything working fine except horn.
  9. Once home, I removed horn button from steering column and removed the little spring-loaded brass contact.
  10. Cleaned with vinegar and wire brush and reinstalled and tested.
  11. Still barely audible. (Could be horn relay or bad ground somewhere)
  12. Got a length of wire and stuck it down in the hole to make contact with the bottom of the cavity where the spring loaded brass contact lives.
  13. Touched the other end of the wire to the center nut of the steering column that holds the wheel on.
  14. Still barely audible. (At this point I'm strongly suspecting horn relay is bad since it's very clacky)
  15. I resolve to buy a horn relay.
  16. Next morning I start driving to work (in the rain) and find that turn signals and brake lights don't work. Everything else works fine.
  17. Oddly enough I tried out the horn and it sounds strong and great this morning. :?
  18. I check the fuse panel when I got home and the turn signal/stop light (14A) fuse was blown (splattered is a more appropriate description).
  19. I replaced it with a new one.
  20. Turn signals and everything else now worked fine.
  21. Brake lights still did not work.
  22. I removed the drivers side tail light cover (in the rain) and inspected the bulb. Looks fine. Reinstalled bulb.
  23. Brake lights still did not work and now the front-passenger side turn signal and drivers side tail light does not work (I suspect water got in the socket when I removed it).
Other pertinent information: The dome light hasn't worked since I bought the truck so I got it working this weekend with a new bulb. I "think" the brake lights were working when I bought it, but I can't swear to it. The cigar lighter fuse was also blown but I don't think that's in the circuit. Turn signals seem to blink fine. Only thing about turn signals that don't work is the lever doesn't cancel/return when using the right turn signal. Left cancels and returns fine.

Any ideas on where to troubleshoot next?
Dave

1965 F-100 Flareside (240 6-cyl)
3 speed. Former military truck.
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Toyz
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Re: first post: brake light diagnosis?

Post by Toyz »

Turn signal flasher and brake lamp switch share the same power supply, thus brake lamps only work "key on". Check for key on power at brake switch. If power reaches switch, jumper from one brake switch wire terminal to the other. ( it's a good idea to unplug ignition coil while key is on for extended time) If lamps then work, replace switch.IMO, don't fall for " low pressure" switch! Ford employs engineers to come up with correct applications, and dropping operating pressure from the original 60 psi to one third of that is asking for trouble!
If you do not find voltage at switch, probe at turn signal flasher. If signals are working, that puts it in the wire rrom flasher to switch.
If power from brake switch, then check from switch to turn signal switch assembly. Everything AFTER switch is common to rear turn signals as well as brake lamps.
Good luck!
Paul
Last edited by Toyz on September 12, 2017, 11:19 am, edited 1 time in total.
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Re: first post: brake light diagnosis?

Post by unibody madness »

WELCOME from California
Chances are your brake light switch needs to be replaced, at the brake master, remove both wires and place a test light between them,one should be hot,the other is a ground, if they both work, its the switch .
Return to bulb you checked, remove lense, wiggle bulb, your turn signals should now work.
Disconnect ground at battery, clean all grounds, at all locations, with vinegar including inside bulb sockets .
Most all your electrical issues will stem from ground issues, block to body, block to frame, just for giggles install one body to frame.
sounds like your horn relay works fine make sure the horn body is making good ground contact as well.
Hope this helps
John
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Re: first post: brake light diagnosis?

Post by Toyz »

Since the horn button simply completes the ground circuit to energize the relay, it is possible that wire may have contacted the brake lamp circuit in or around the column, blowing the fuse. Thus, follow up by after the repair by blowing the horn while turnng the wheels to help avoid any recurrence.
Paul
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Re: first post: brake light diagnosis?

Post by Toyz »

unibody madness wrote:WELCOME from California
Chances are your brake light switch needs to be replaced, at the brake master, remove both wires and place a test light between them,one should be hot,the other is a ground, if they both work, its the switch .
Return to bulb you checked, remove lense, wiggle bulb, your turn signals should now work.
Disconnect ground at battery, clean all grounds, at all locations, with vinegar including inside bulb sockets .
Most all your electrical issues will stem from ground issues, block to body, block to frame, just for giggles install one body to frame.
sounds like your horn relay works fine make sure the horn body is making good ground contact as well.
Hope this helps
John
John, the switch output is NOT a ground, rather it is the power wire feeding the brake lamp circuit of the turn signal switch. The horn relay ( or it's ground) is quite often the source of a " weak" horn, although the horn itself should be adjustable.
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Re: first post: brake light diagnosis?

Post by redstone65 »

Toyz wrote:the switch output is NOT a ground, rather it is the power wire feeding the brake lamp circuit of the turn signal switch.
Last night before giving up I put the black side of the multimeter to the frame and the red side to each of the brake pressure switch wires in turn. I got zero voltage on both wires with key in the on position. Does that mean either broken/grounded wire or bad turn signal switch?
Dave

1965 F-100 Flareside (240 6-cyl)
3 speed. Former military truck.
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Re: first post: brake light diagnosis?

Post by agjames96 »

I fought brake lights and my problem was finally solved by cleaning connector where harness goes through the firewall. It was loose and some of the contacts had begun to corrode.
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Re: first post: brake light diagnosis?

Post by Toyz »

redstone65 wrote:
Toyz wrote:the switch output is NOT a ground, rather it is the power wire feeding the brake lamp circuit of the turn signal switch.
Last night before giving up I put the black side of the multimeter to the frame and the red side to each of the brake pressure switch wires in turn. I got zero voltage on both wires with key in the on position. Does that mean either broken/grounded wire or bad turn signal switch?
That simplifies that part of the search considerably! Check the two wire connector at turn signal flasher. Since your turn signals are at least partially working, problem is in that feed wire from the flasher input to the pressure switch, and may well be as previously suggested, at the firewall connector.
Paul
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Re: first post: brake light diagnosis?

Post by redstone65 »

Thanks all for the help.

Which one is the turn signal flasher?

Image

or

Image
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Re: first post: brake light diagnosis?

Post by ThinLizzy13 »

The bottom picture is a flasher. The top picture is a condenser.
'63 F100 223 3OT
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Re: first post: brake light diagnosis?

Post by redstone65 »

ThinLizzy13 wrote:The bottom picture is a flasher. The top picture is a condenser.
There doesn't appear to be anything connected to the condenser, and I don't see it on the wiring diagram. Probably a left-over from something? This used to be a military truck.
Dave

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Re: first post: brake light diagnosis?

Post by unibody madness »

Your right Paul, do not know what I was thinking, but am I correct in thinking that a test light between both wires should light? I do know if the two are touched it should light the brake lights.
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Re: first post: brake light diagnosis?

Post by Toyz »

John, yes, if circuit is complete to at least one brake lamp, test lamp should light. However, it would also light if any part of the downstream power circuit were seeing any sort of ground or short.
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Re: first post: brake light diagnosis?

Post by redstone65 »

unibody madness wrote:Return to bulb you checked, remove lense, wiggle bulb, your turn signals should now work.
You're a genius. The bulb works after a jiggle.

But, now when I enable the right turn signal the rear right bulb blinks but the front right bulb doesn't blink. And when I enable the left turn signal the front left bulb blinks but the rear left bulb doesn't. I say it doesn't blink, but it actually does blink very very faintly. It's almost imperceptible.

I checked voltage at the flasher terminals and got 12v when using the left and right turn signals, but got zero voltage when pressing the brake pedal. Would that suggest the turn signal switch is the culprit?
Dave

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Re: first post: brake light diagnosis?

Post by Toyz »

Should have constant key-on voltage at orange/yellow (and red) wires at flasher. This terminal also feeds brake switch. Since the flasher is upstream from t.s. switch, it should show power any time key is on. The output side of the flasher should show pulsing power when t.s. switch is energized.
John is likely correct as to the turn signal problem; sounds like a poor ground or bad bulb contact, especially since you noted a faint pulsing.
Still need to get power to brake switch from that flasher feed terminal; If wire is hot at flasher, I'm still betting on a poor conection at firewall.
Once you have power to brake switch, we can check the switch itself and on downstream to the turn signal switch if needed.
Paul
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Re: first post: brake light diagnosis?

Post by redstone65 »

10-4. Thanks so much guys.
Dave

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Re: first post: brake light diagnosis?

Post by redstone65 »

Making it to the weekend so I can have time to dig in and diagnose this problem, but new behavior today. Turn signals now flash rapidly with no audible clicking. Just posting this for completeness sake. :-)
Dave

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Re: first post: brake light diagnosis?

Post by Toyz »

Two common possibilities for the new problem: short circuit after flasher, or flasher chose an inopportune time to fail. If same pattern regardless of which turn signal, and all are illuminating, with no clicking felt with key on, signals off; most likely flasher. My suggestion would be an electronic replacement, just in case you might pull a trailer, or upgrade bulbs.
Paul
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Re: first post: brake light diagnosis?

Post by unibody madness »

I agree, after cleaning up all your grounds, inside of socket housings, and testing bulbs this weekend, you may find your problem solved. Sometimes if one of your bulbs go out the other bulb on the same circuit will pick up speed due to lack of resistance at the flasher.
It is important to clean and adjust sockets,bulb bases, and all grounds well to insure good contact for electrical system health.
Living on an extreme budget back in the early 70's forced me to double check the basics several times before replacing or paying someone else to replace/repair.
Now with the internet you have people who can help with their knowledge and experience like Paul, that make life much easier. I know I have been saved many times by the help available on this site,instead of trying to muddle through on my own.
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Re: first post: brake light diagnosis?

Post by redstone65 »

Well, all is now fully functional. We removed all 4 bulbs and inspected them. One bulb had a blown filament and another looked fine but showed no continuity on the multimeter. Also, they were of 3 different types (2 were 1157, one was 1034 and another was 1154). So I looked up the proper type in the shop manual (all should be 1157) and we replaced all 4 of them.

Now I started getting voltage at the brake pressure switch.

Tried everything out and it worked, but some of the lights were still dimmer than the others.
Toyz wrote:Two common possibilities for the new problem: short circuit after flasher, or flasher chose an inopportune time to fail.
Just for kicks, we went ahead and replaced the flasher and then everything started working perfectly. :D

At this point I tried out the horn again since all of this started with the horn. The horn was back to sounding weird and croaky. This made zero sense if the wiring diagram is correct since that circuit doesn't touch the TS/brake light circuit at all. We found a partially melted 2-wire connector coming out of the horn relay and I still suspected the horn relay was bad. We replaced the melted connector and the relay and now the horn sounds fine.

Woo!
unibody madness wrote:Now with the internet you have people who can help with their knowledge and experience like Paul, that make life much easier.
Thanks so much for the help guys. Very much appreciated.

One last question on this: did the mismatched bulb types make any difference? If they should all be 1157, would that 1034 have caused an issue? Just curious since I don't know the difference between them.
Dave

1965 F-100 Flareside (240 6-cyl)
3 speed. Former military truck.
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