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1941 Chevy AK Truck - Brake Switch Question

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1941 Chevy AK Truck - Brake Switch Question

gonzonerds gonzonerds
New User | Posts: 3 | Joined: 02/14
Posted: 02/27/14
07:51 AM

I have a 1941 Chevy Truck that recently purchased from a Family Member.

Some re-wiring and such had been completed on the truck prior to my purchase.

Went to drive it a few weeks back for the first time since purchasing it.

After 10 minutes of driving the truck the brakes and brake lights went out at the same time - no brake pressure - brake pedal went to the floor.

Pulled over and removed the metal floor panel to look at the master cylinder.

I noticed that front terminal off the the brake switch that screws into the master cylinder was melted and smoking - I took the cap off the master cylinder and the brake fluid also appeared to be hot.

I checked to see where the melted wire off of the brake switch went, it went thru the floor board in the cab and up to the light switch located behind the dash.

There is like 6 terminals on that light switch - that wire was doubled up onto another wire on a terminal - I noticed that there was a empty spot on a terminal with a fuse on it - should that wire be attached to that terminal with the fuse?????

Or is there another reason like a bad brake switch at the master cylinder or bad wire set up at the tail lights??????

Thank you for the help!!


wayne712222 wayne712222
User | Posts: 180 | Joined: 10/13
Posted: 02/27/14
01:38 PM

is it still original wiring?????

or has it been updated to 12 volt and a new harness???

i did not see a 41.. but i did see a 40 and a 42 diagram if you have the original

40Chevytruckwiringdiagram Zps9efd9ace

42Chevypickupwiring Zpsa081d0b2  

wayne712222 wayne712222
User | Posts: 180 | Joined: 10/13
Posted: 02/27/14
02:01 PM

if you need more help..

i don't know why the master would be empty except you have a leak someplace..

please examine your entire underside of the truck for signs of leaking fluids..

brake fluid will wash off with water...

oil won't...

you could have a bad wheel cylinder.. brake shoes out of adjustment that allowed the wheel cylinders to extend past the end of their stroke..

you could have a leaking brake hose.. a leaking brake line.. a leaking master cylinder.. even a missing master cylinder cap seal..  as the brake excess brake fluid in the master cylinder bore sprays upward when the pedal is depressed.. this can blow the fluid out of the reservoir until its empty..

glad you were able to get it stopped before anything caught fire..

since you have to probably rewire that circuit.. please install a small fuse block ..

these should be available at almost any parts store in the HELP section..

if you don't have the special pliers to crimp the terminals to your wiring.. you can carefully solder the wire . or just tin the end of the wire.. then crimp it as best you can then barely heat it. just enough to melt the solder to the terminal.. not enough to have the solder wick up the wire where it will harden it and cause fatigue issues..

please use an amp meter to measure the load on the circuit and use the fuse that's 5 amps larger than the max load..  so the fuse blows protecting the circuit and wiring..

85668Dormanhelpfuseblock Zpsb85414a6  

wayne712222 wayne712222
User | Posts: 180 | Joined: 10/13
Posted: 02/27/14
02:04 PM

if you climb under the truck.. and take some pictures.. you can upload them to photobucket  and paste those links here.. so we can see what you are to get you better answers..  or just to show the truck..

there is a readers rides section around here someplace..  

gonzonerds gonzonerds
New User | Posts: 3 | Joined: 02/14
Posted: 02/27/14
03:47 PM

Thank you for the reply!

The Truck is still 6 volt - Wiring has been upgraded.

I didn't see any leaks under the truck nor at the wheels.

Original brake set up - with new brakes.

Diagram you sent me shows that wire from the brake switch being attached at the light switch at the fuse location - which is an empty terminal on my truck.

My wire from the brake switch presently is attached at the light switch on top of another wire.

Could that be the issue or maybe a bad brake switch??


wayne712222 wayne712222
User | Posts: 180 | Joined: 10/13
Posted: 02/27/14
08:06 PM

is the brake light switch on the master cylinder  and looks like an oil pressure switch..

if so.. then that switch could have failed and shorted the wiring to ground..

the slightly later trucks went to a lever type switch ...

let me see what i can find for images..

looks like it uses a snap on terminal type switch..

Chevytruckbrakelightswitch Zpsc49e203e

Standard Motor Products SLS27 - Standard Motor Brake Light Sending Units
Stoplight Switch, OEM Replacement
Part Number: SMP-SLS27


Duralast/Stoplight Switch
Part Number: F4805

Smp Sls27 W Ml  

gonzonerds gonzonerds
New User | Posts: 3 | Joined: 02/14
Posted: 02/28/14
08:00 AM

Yes the Pic is the same that is installed on my truck.  

wayne712222 wayne712222
User | Posts: 180 | Joined: 10/13
Posted: 02/28/14
10:13 AM

the switches are cheep... under 20 bucks..  might be under 10..  i posted the 2 most common part numbers to save you time..

i am going to love the face on the parts clerks.. when they ask you .. year make and model..  yes.. i would like a brake switch for my 41 chevy pickup ..

if they look around.. say.. i am NOT fred flintstone and you won't find barney standing beside me..  barney is out in the car..

most parts stores will actually have this switch in stock.. if you ask for it by part number...

don't throw the old switch out..

and please.. find a 12 pointed socket to install it..  do not use pliers.. pliers distort the crimp slightly and can cause issues..

refill the master.. bleed the brakes.. see what happens..

look for fluid on the inside of the backing plates. or on the inside of the tires..

that would indicate a leak..

when these switches fail..  they can leak..  but brake fluid has some conductivity.. it will short to ground if it gets in touch with the power wire on the brake light switch..

and why buy a proper socket that fits this strange shape.. its cheeper than sheet metal replacements for your truck front end..

once you get the switch install.. and some brake pedal operation restored..

sit in the truck.. place foot lightly on the brake pedal.. and see if it slowly sinks to the floor.. that would be very bad..

do that several times..  then look for puddles..   not that puddles.. the one who followed hewey and dewey into the bar..   puddles of brake fluid..

sorry.. it's raining here in so cal for the first time in a while..  and i am looking for wet humor..