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Brake light switch


Jerry T

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Question for all you Mopar guys...I'm just starting to restore this 51 desoto and the masrer cylinder was leaking. While I was removing it, I found a brake light switch bolted to the master cylinder with a makeshift plate and when i ordered a new one it was a hydraulic switch?  Which one was original equipment on the 51  and does someone have a pic of how it installs as mine has two holes in the end which looks like front and back?

 

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My ‘38 even has a stock hydraulic activated switch. 

 

Follow your brake line along the LH side of the car frame. Under the seats look for a hydraulic switch. 2 wires plug into it. Brake lines screw into it. See here, black arrow pointing to it in my ‘53-‘54 parts manual.  Yours will likely be similar. 

 

 

B392664F-548C-44C4-851B-D23E68A70906.jpeg

Edited by keithb7
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Maybe Desoto was more fancy and put the switch in the line, My truck has it on the master cylinder.

I suspect the switch would work just about anywhere on the system, as long as wired correctly and getting pressure when brakes are applied.

 

These are things that previous owners may have changed, and they used what they had to make it work ....

Think you need to decide at what level of restoration you want to do, how important to you, is the switch installed in the exact factory location?

IMG_20191012_153814352.jpg

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3 hours ago, Jerry T said:

Question for all you Mopar guys...I'm just starting to restore this 51 desoto and the masrer cylinder was leaking. While I was removing it, I found a brake light switch bolted to the master cylinder with a makeshift plate and when i ordered a new one it was a hydraulic switch?  Which one was original equipment on the 51  and does someone have a pic of how it installs as mine has two holes in the end which looks like front and back?

 

Jerry: The first question and I will assume that the answer is NO. From your question we can assume that you do not have a service manual or a parts manual for your car.  This is the first two items that you need to purchase inorder to work onyour car.  The service manual would have an line drawing of the wiring systems and will show where the original brake switch was located on the frame or on the end of the master cylinder.  I am not trying to be provide a smart reply but get a reproduction copy for your own education on the car.  After doing some research all of the members are willing to provide you with more input to your questions but you need to get up close to the car and get to know your car.

 

We all do not know all of the answers we will give it a good try.  Also sometimes in the service manual you will see pictures of the various parts and this will also help you learn about your car. As you can determine I have a 39 Desoto and my brake switch is just in front of the master cylinder and is attached to a four way  brass connection.

 

Rich Hartung

Desoto1939@aol.com

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@desoto1939 is right. A service manual is so very important if you own, and want to work on these great old cars, yourself. I have spent countless hours researching books in a small vintage Mopar library that I seem to be building. I cannot imagine how I’d have progressed without my old books. 

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on 49 to 52 cars, the Stop light switch is mounted on a junction block just forward of the left rear axle.     Standard Motor Parts   "SLS" 24 will work  although wire terminals on SLS 23 or 25 may be more suitable.

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First, Iwant to thank you guys and the comments on this forum.  I did buy the cd shop manual for the car and will use it accordingly ...and yes Im with you on the need for a manual...I'm an HVAC instructor and I tell my students if you screw up a 30.00 part because you didnt know what your doing you could had bought the manual:)    So now I need to ask you mopar experts another question ...I just purchased a new wiring haress for the 51 desoto as the existing  was ate up by rats.  If you were restoring and trying to keep it as stock as possible would you wire it in as 12v negative ground or stick with the 6v positive ground?

 

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Calculate the loads on each circuit and confirm the wires in the new harness are heavy enough if you stay with 6v. Harnesses intended for 12v may have wires that are too light to handle the heavier currents in a 6v system. This is especially the case with battery cables and headlight circuits. Battery cables need to be BIG (my car has neg ground):

 

battery-cables.jpg.a6d038db0ab055e49f8936293293988a.jpg

Edited by Sam Buchanan
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6V positive ground here in my 1953 Chrysler. Works just darn fine when maintained properly. Good grounds and 00  battery cables are a must. My lights are bright. Never had a starting problem. Only thing I can think of to deal with, is my iphone charger is a portable self-contained booster pack that I keep in the trunk.  I could buy and wire up a 6V/12V converter. No big deal to me. Not really needed. Stepping back to 1953 is pretty fun and having no cell phone to bug me is a plus sometimes. 

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16 minutes ago, Sam Buchanan said:

Calculate the loads on each circuit and confirm the wires in the new harness are heavy enough if you stay with 6v. Harnesses intended for 12v may have wires that are too light to handle the heavier currents in a 6v system. This is especially the case with battery cables and headlight circuits. Battery cables need to be BIG (my car has neg ground):

 

battery-cables.jpg.a6d038db0ab055e49f8936293293988a.jpg

Sam I noticed you have an alternator....did you step the voltage dn from a 12 v alternator to the 6 v battery?

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2 hours ago, Jerry T said:

Sam I noticed you have an alternator....did you step the voltage dn from a 12 v alternator to the 6 v battery?

 

Jerry, it is a 6v alternator.

 

https://www.qualitypowerauto.com/category_2/Special-Applications--6-Volt-8-Volt-and-12-Volt-Positive-Ground.htm

 

I got tired of messing with the old genny and regulator and when they died I wasn't going to throw good money at them. The alternator is a huge improvement in performance....and I hope reliability. The alternator is internally regulated....what you see where the regulator used to be is a large fuse.

 

Battery cables are available here:

 

https://www.batterycablesusa.com/0-gauge-battery-cable-with-ends-1-0-awg

Edited by Sam Buchanan
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OIC   I didnt realize they even made a 6v alternator  That might be an option ill consider...How hard was it to convert to negative grd?

 

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12 minutes ago, Jerry T said:

OIC   I didnt realize they even made a 6v alternator  That might be an option ill consider...How hard was it to convert to negative grd?

 

 

Reverse the battery, coil, and ammeter connections. But positive ground alternators are available, positive ground works great, and it is required if you have an original radio.

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