[Gazza10]

Need some help with a Brake light problem on a 67. Power Assisted Drum Brakes all round as standard
At rest brake lights work fine A slight jab of the pedal and on they come BUT as soon as I start driving I need to jump hard on the brakes for them to work. Bloody dangerous as I can't "feather " the pedal to toggle the break lights.
Blinker lights work fine and seem do do what they should
History
I changed the original steering wheel to a Grant All seemed OK . Some months after changing Steering wheel backed car out of garage to let it run for a while as it had not seen the daylight for around 6 weeks.
Back in garage and noticed a ticking sound when car shutdown. Noticed tick coincided with interior light flickering on and off Quick disconnect of battery and found Grant horn button red hot. Revisited the insulation I had on the horn wiring and all seemed well Horn works etc. Some time later whilst on road informed I had no brake lights Tested at rest and all fine so assumed dirty switch. Problem however has continued _ Brakes test fine at rest but when travelling I have to slam them on to get the brake lights to work. I have changed the brake light switch and no change. Even added a 1/8" plate to the contact area of the switch and found at rest the brake lights stayed on so clearance or play doesn't seem to be the problem and hence removed the additional plate
Only other mod has been to add a small tacho
It's doing my head in - where do I start???
Thanks in advance

 

[RoddinRob]

Hi...

Electrical problems can be a bear to sort-out. I've done a lot of automotive wiring over the years & seen some interesting problems. Some the result of bad practice, some the result of failures, grounds rotting off, etc.

Reading what you've written, a few things come to mind:

Changing your wheel & adding a tach means you've had to touch the wiring. I changed the column in mine & had issue with one of the turn signals because one of the pins on the column wiring connector popped out of position. Point being, you should verify the integrity of any the connection points you've touched.

Grounding is another issue that can result in weird symptoms. Absence of a ground in the right place means that the circuit will try to find another path. I had a headlight ground that rotted off one time & every time I put the turn signal on that side, my headlight & turn signal would alternate off/on because the ground was trying to go through the headlight filament to get to that ground. If memory serves; there is supposed to be a ground on the column. Did that get re-installed? If it is hanging loose & it makes contact when you hammer the brake while the car is moving the wire may be dangling around, but when the car is still it isn't... Something silly like that.

Is the tach wiring correct/working properly? Where is that ground connected?

Lastly (& I've seen catastrophic results of this one)... Nothing will burn a car down faster than an electrical fire. Its effectively a cascading failure. Once a circuit pulls enough current to melt the insulation, that wire melts into other wires, shorting them out & so on... The only thing to do at that point is pull the cable off the battery, or let'er go & call the insurance. You said your horn button was shorting/overheating. That's bundled-in with your column wiring, which is in close proximity to the brake wiring... It's possible you have an intermittent short. The other thing I've seen happen is the wiring insulation gets very brittle with age - especially if it's seen a lot of current & when you handle it, insulation breaks away/falls off leaving bare spots... Another possible issue for short circuits.

I know it's tough to get in there - not a lot of room (I'm 6'-4" & 260lbs)... but I would get a good light in there & check all connections & verify grounds, follow the brake circuit wiring. Having a wiring diagram & volt/ohm will also help.

R.R.

 

[07redstang]

You need to follow the circuit with a test light and see where it loses voltage, It probably is not your brake light switch, it may be in the turn signal switch. Since you replaced the steering wheel.

 

[Travis98146]

If you don't have one, get a wiring diagram to see where your brake light switch gets it's power. A hot horn button points to a short to ground in that circuit. Most horn circuits are wired hot to the battery at all times. I'd disconnect it's supply until you locate the short.

 

[Gazza10]

Thanks for your insight I have just started the car and left it in park checking Brake lights after the vacuum has cut in to the booster and has pulled the pedal a bit towards the floor. The brake lights work but require a bit more pedal movement than when testing with ignition off. Saying this it is no where near the pressure I need when I am travelling at speed in the car and want to pull up. They are also slow in reacting to standing the car on it's nose !! I am unable to toggle the brake lights at all in this scenario ie when travelling along.
I checked the emergency lights and blinkers and all are OK. Horn works OK

 

[Charles Reeves]

I finally gave up on trying to get the pedal mounted brake light switch on my '66 to work and put a pressure switch on the brake line going to the front brakes.

 

[K4JOE Joe]

If you have mechanical brake light switch, here is video on how to adjust. This video shows using a shem. I have just bent the tab that holds the spring in to do the same thing. Make sure you adjust ( bend) in correct way to decrease the amount of travel your brake pedal travels.

If you are useing ( has been replaced with pressure switch) be sure you use the "low" pressure type... they make two pressure switches--low and high pressure.

If you have excess travel-- view this vedeo on how to adjust the brake push rod in the master cylinder

/www.youtube.com/watch?v=GrFEzfDnzqM

also here is a wiring diagram for your Mustang.

1967 Mustang Wiring and Vacuum Diagrams - Average Joe Restoration

Hope this is of some help.

I am not the "average Joe" but still Joe


Joe

 

[Gazza10]

1967 Mustang Brake light problem continues

Thanks all for the insight Still have the problem although I have not gone too far with the investigation other than give some wiring a wriggle !!
Question - If it was an earth problem and seeing many bits share earths if I was use a jumper lead to establish another earth on the tail light globe ( I assume the earth is the spade connector on the ring on the globe sticking out of the mounting cup ( Am I correct ??) would this do any damage and if not would it be a pointer to an earth problem??
Guess I am looking for an easy way to start before chasing all the earthing points , removing the steering wheel etc
The replacement brake switch I used was a Scott Drake with no indication of "pressure" It is doing exactly what the original was - Works fine at rest but when travelling have to stomp hard on the pedal for brake lights to work and even then they are sightly delayed in lighting up. Surely there is no correlation between auto transmission gear selection and the brake switch?? Is there??
Also I note that the proportioning valve which I assume would be standard and original to the car has an electrical connection coming out of it from a nylon fitting - can anyone explain it's purpose?? Where does it terminate? Would it affect brake light operation at travelling speeds?

 

[RoddinRob]

That electrical connection out of the proportioning valve would likely be for the 'BRAKE' fail light on your dash.

 

[baylensmanfl]

Most likely cause is the brake light switch it self. There are three nylon bushing that get brittle with age if either fails the switch may "****" sideways causing the issue you're talking about or the opposite issue some cases where the brake lights won't shutoff.

 

[Gazza10]

This far I have as follows -Still no success. Problem still exists ie Brake lights at rest , None when travelling along , even at slow speed. Have to bring the car to rest and the brake lights come on in just under a second after coming to rest
I now have attempted to adjust the brake light switch without any change to my problem I have also been placing various thickness shims on the rod /switch contact surface to minimise the travel distance but problem still exists. I even placed a shim which would have been just under an 1/8" between the contact surfaces and this resulted in the brake lights being on at rest. Run the car at about 5 mph like this and thought if the problem was some sort of short the lights may turn off BUT no they stayed on.
I am at a loss.
What would you think if I disconnected the blinker circuit at the globes and tried the brakes again Might it point to a problem in the turn/brake switching? Would it cause any wiring damage if I made sure any bare ends where well insulated before adding any power?
Could the problem be voltage / regulator related with possibly higher volts with the engine under load causing the problem??

 

[K4JOE Joe]

If, as stated: " Problem still exists ie Brake lights at rest ".
If brake light stay on when car is at rest , then you need to adjust the Brake Booster Pushrod Length.

View this video:

It is for a 2004 Grand Marquis, but principle is the same.

Joe

 

[Gazza10]

Thanks Joe The brake lights stayed on at rest with a shim in between the switch contact surface and the booster rod. Removed the shim ( about 1/16 " to 1/8 " thick) and lights off at rest and moving . I have since been cutting up a jam tin lid ( very thin) and I presently have 2 pieces acting as a shim and lights are not on. Waiting for a spout to see if any diff when running. Also see next as to what I have been up to chasing the problem without success!!!
I have tried bending the tabs , probably up tp 1/8" forward without success atm . I have cleaned the battery lead at the block end , and had a quick look over the wiring, even disconnected the taco I installed and still no joy. Seems when at rest less pedal travel and I can get the brake lights to toggle. On starting the car and the vacuum booster doing it's thing I have to move the pedal further to toggle the brake lights yet when I start moving NO brake lights until approx 1 second after the car comes to rest. I ran the car at dusk with the lights on ( using wife as a spotter - yeah I know first mistake !!) and still no change to brake light operation ie OK at rest and not coming on till car has stopped after rolling down the road. Wife reckons no change in brightness of lights when they did come on with headlights turned on , although I do notice a change when stopped in the garage with and without engine running. I will continue bending the tabs until I reach the point of lights permanently on the back off a bit to the not on spot. Question - Is the flat on the rod long enough to meet the tabs before the centre of the switch? ie will the rod flat miss the tabs even if they are bent? Went to get a relative measure last time under but couldn't quite get it accurately that time
Anything else anyone could suggest I check?
What about disconnecting the blinkers to see if the problem lies in the cut out switch between blinkers and brake lights, although it works perfectly at rest
Thanks in advance

 

[JustAnotherRuki]

Can you adjust your brake pedal rod? say bring it up a little higher by turning the rod CCW. To me it looks like this problem is pedal related.





J

 

[Gazza10]

Do you mean the booster push rod ? Can the length be adjusted from inside the vehicle by disconnecting it from the pedal and turning it or is it adjusted at the booster itself as per post K4Joe earlier ? I am aware of this adjustment but not from inside the vehicle !!

 

[Gazza10]

Joe I am struggling to get the '67 schematics for some reason I did ask for a 67 and got a 66 for exterior lighting, turn and horn. Is the 66 wiring the same as 67 in this area? Thanks in advance

 

[JustAnotherRuki]

Do you mean the booster push rod ? Can the length be adjusted from inside the vehicle by disconnecting it from the pedal and turning it or is it adjusted at the booster itself as per post K4Joe earlier ? I am aware of this adjustment but not from inside the vehicle !!

Yep that one! My old brake booster had it and the new one i bought has it as well, although yours being a 67 i don't know if its adjustable. Its a pain to get under there but try reaching for the rod and if you feel threads around the shaft is adjustable for sure. Remove clip, slide it out of the peg and turn CCW to bring it up a bit. I hate dealing with the brake switch when doing this but there is no other way around it.




J

 

[Ivy66GT]

Joe I am struggling to get the '67 schematics...

I'm not Joe, but...

The '67 may be a little different but not much. I think the one you want is attached? Its drawn a little differently than the '66 ones which makes it a little harder to trace the wires. Instead of each wire being drawn from end to end, a line can represent a bundle of wires. You have to keep track of the numbers for the wire colors to know where they enter, and then later exit the bundle.