Here's what happens:

When I step on the brakes, the right light comes on after what I consider to be excessive pedal motion/effort, but It DOES come on.

When the right blinks ON, the left JUST starts to glow, then increases in brightness SLOWLY.

What's up with that? I looked at a factory manual, and it appears that the switch is at the master cylinder? Can my original, gummed-up M/C affect the switch like this?

The only thing I can think of besides a gummed-up M/C and/or switch is a faulty bulb, and for all I know the bulbs may be original.

If it was just an instantaneous dull light, I might suspect a bad ground, but the fact that it brightend slowly baffles me.

Anyone?

 

I would try to swap out the switch first as its the cheapest and easiest to do...switch shouldnt be more then 5 bucks. Aside from that, look to see if the tail harness has been spliced into at some point in between the 2 sides.....

Good luck, cs65

 

No, it can not.

A weak or dirty contact in a turn signal switch & a corroded/ weak ground in the hraness / circuit can recover & become brighter over time, until it is turned off again, under some circumstances, so don't rule that out.

The brake light switch in the master cyl only closes a power circuit going to turn signal switch where the current is distribuited or interrupted depending on whether there is a turn indicator light active or not. The turn signal switch also keeps front turn signals from lighting when you step on the brake pedal. The turn signal switch is what decides which brake lamp(s) will light up, and which one will not.

Your problem is either ground related, such as wiring or grounding circuit, a bad bulb socket, or a T-Sig switch getting ready to "go to out lunch".

The pressure activated "Wet" Brake light switch is single pole single throw & is either On (circuit closed) or it's Off (circuit open).

Start with a test light or a VOM and check out what hapens after the T-Sig Sw.

FBp

 

For what it's worth... It is very common for the signal light switches to go bad in these trucks. Sold tons of them in the 70's.
nn
Barry

 

Hold on here, you mean the STOPLIGHTS are wired thru the TURN SIGNALS?? What is the reason for that? WHy should a brake light have anything to do with a turn signal? Shouldn't the two systems be completely independent?

You mentioned the turn signal switch keeps the front signals from "signalling" when the brake is on-what about sitting at a light trying to turn left with your foot on the brakes; you mean the people coming at you don't see a turn signal?

And how does a turn signal switch determine which brake light is on?

I have to confess I am flabbergasted at the design intent behind what you're saying, and I'm not sure I understand it.

What I DO understand is the switch at the M/C is either on or off, so if my brake lights are coming on at all I'll eliminate that as a trouble spot.

 

Yes, it controls the brake lamps. It's wired thru for the reasons FBP explained. I can't count how many I sold back then. Very common problem. I would suggest you get a wiring diagram on the truck. I'm not an electrical genius by any means, I can't explain it as to why it's wired thru. I just know it's a design that wears out over time. If yo want me to locate a switch, send a PM to me and I'll help you out.

Barry

 

Okay, I said "the turn signal switch keeps the front signal lamps from lighting up when you step on the brake pedal." which it does and that's why it has the power to the brake lamps routed through it.


You asked "it keeps the front signals from from signaling?"-- which it does not.

In fact T/S Switch is what allows front signals to signal, just like it allows rear brake light to signal when you step on brake pedal while your turn indicators are engaged.

You also ask if brake lamps are independent of rear turn signals, they are not.
In fact they share same filament inside rear bulbs. Tail lights are independent of brake & turn signal lights. But as I just said, Brake & Turn Indicators use the same filament. That is why they both are routed thru a turn signal switch up in your steering column mast jacket, just like I told you they are.

The determination is made internally by a series of contact points that either engage or disengage dependent on position of turn signal indicator lever & what you are or are not doing with the brake pedal.

When contacts wear, or plastic goes bad or grease contaminates contacts, the end net result is the symptom you described to begin with. As heat changes things, during operation of the switch with live current going thru, symptoms it displays can change. Never the less I would bet your problem is in your turn signal switch or wiring after it.

you are correct, if the "wet" style brake lamp switch lets current through on application & interrupts current on release it's functional. I gathered that in your explanation iniytially. That's why I made the suggestion I made about your T/Sig switch being the problem. You may just get away with a good cleaning with "Brake Kleen" solvent.

If you have a VOM or a test light check it out as I said. If you have the broblem coming "out" of the steering Column, your problem is definitely in the switch. You'll not know what it is until you pull strg wheel & inspect it. . . .

If you get rear ended without functional brake lights you will most likely be found to be at fault in most states in the USA. That can be an expensive error if there is injury involved in such a wreck.

FBp

 

NOW I understand, and it came to me in a "flash" (no pun intended)!

I ALWAYS wondered how that single 1157 bulb with only (2) filaments handled the running lights, brake lights, and turn signals (3 functions)!

Without a wiring diagram in front of me, what you're saying is that with the brake pedal depressed (for example), the brake light is "on", but if I were to also hit the turn signal switch, that same filament would then be fed by the flasher circuit and would flash as a turn signal in both front and rear. The T/S switch PREVENTS the front T/S from illuminating when I merely step on the brake.

I get it now, didn't mean to come across as dense.

Now where to get a T/S switch?

 

Uhh get in touch with barry (he said he could get you one).

 

That switch ( c2tz 13341-d) for64-66 4X4 trucks, is still available from Ford for $64.45 retail. I checked this morning.

Barry

 

I just noticed that the P/N you gave was followed by the model designation "4x4". Mine is a 2-WD. Does that make a difference?

 

mY MISTAKE, i THOUGHT YOU HAD A 4X4. yOUR PART NUMBER IS c9tz 13341-c FOR 2X4. It's still availble thru ord, $56.03 list price. Where are you? I thought you were in Connecticut? If so, I'm at Dowling Ford in Cheshire, I could get it for you at a discount. Let me know,

Barry

 

No, no, no, don't even go there brider, Not Questioning is being "Dense".

In order for us to learn we MUST ask questions. Those of us who don't ask questions are doomed to remain dense, make some wierd assumptions or else have a lot of "little fires" in our wiring systems, if ya catch my smoke there.

One great thing about learning stuff is then we can share it with others and an entire population grows smarter as a result of that. Another great thing about increasing our knowledge, as we learn more we begin to see "see the Light" [that's an intended pun].

As for your explanation/ question above, you got it! That's exactly how it works.

So if this was a "Flash Quiz" [another pun] give yourself 100% for an a A+ grade man!
It took me a long time to learn read the instructions on new stuff I bought & tried to put together or hook up. I also wouldn't stop for directions even if I had no "true klew" and was going in circles to nowhere. I had figured people would think I was stupid if I had to ask. Eventually I realized it was much more stupid if I didn't bother to ask.

But it's better to humble myself & get things right, than to think I know stuff, fancy myself as being able to figure things out, or believe I'm able to proceed without any help, then watch my new Doo Dad or Gizmo suffer a catastrophic failure because of my ignorance, inability, lack of skill or lack of comprehension.

I also learned to only make statements on topics or things I'm sure about, but I still make mistakes because I'm human. It's what humans seem do. It's also how we learn. Mistakes are what taught me to seek help & information when I get stumped.

I'm glad the brake light & turn indicator circuitry all makes sense to you now. Wait until you run across a system with 4 way hazard flashers !
That T/Sig Switch looks like a Spaghetti dinner in technicolor, with loops & bypasses and multiple switches too. IMHO the absolute worst is a T/Sig Sw for late models with a tilt wheel and cruise control. . . .
CIAO
FBp

 

You speak like a man who's been there and back, FBP. Thanks for your input.

Now, Barry: Ain't we got fun! You work at a Ford dealer?! How handy is that!

Yes, I do live in CT, little town of Orange, just west of New Haven. And I DO need one of those switches, so if you can swing a discount, do you just want me to send you a check, and when it clears you can just buy the part? Will your dealer also ship parts? I can send an extra amount to drop it in the mail-

Let me know your address and $$ in a PM and we'll go from there.

TB

Wait a minute-Cheshire? I'll just pick it up!

 

I sent you a PM, They stock it in our Windsor, Ct depot. I will have it monday morning( actually tomorrow morn, but we are not open on Sat. )

Barry