Full Size Jeep Network

Stooper easy to do. Drag the brake light wires into the cab and off the (seized) master cylinder pressure switch. Thin aluminum bracket screwed to the neutral safety switch and a $7 NAPA GM switch. Done.


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Wow! You done it well. I think the attached snap was taken hardly but still seems of wonderful quality.

I like the alternative, clean and simple!

The new aftermarket hydraulic switches are terrible quality. A mechanical switch works much better. I like this solution.

What's the Napa part number?

This looks like it: https://www.napaonline.com/en/p/TWR8715 ... sionRank=4

If I understand correctly there is a pressure switch on the master cylinder that closes the circuit to the brake lights? If so what vehicle is this system on? I have never seen this on any FSJ.

The OP fixed a really dumb mistake from the factory. Hydraulic brake light switch is just another leak waiting to happen.
Switches leak fluid out and air into the MC. Had a fun ride down from Tahoe because of this. Good job with the write-up
and photo. Just another example of a company choosing cheap over right.

1972 and prior FSJs used the hydraulic brake light switch, 931216. In '73, they changed to a mechanical switch under the dash.

The quality of the aftermarket hydraulic switches is now terrible. This is an ongoing problem for '71 and earlier CJ owners, and I presume all '72 and prior FSJ owners. The main issue has not been leakage, but that they simply stop working after a few months of service.

https://www.rockauto.com/en/partsearch/?partnum=931216

Regarding LKMarsh's comment about cheap vs. good, I suspect this was the common and appropriate technology for ... the 40s and 50s. In the CJs, it's clear that this technology was simply a carry-over in models that were developed in the prior decades. Kaiser-Willys was never a big-money enterprise, and I suspect that - with the FSJ - it was a matter of using existing workable parts for a new design. Can't take R&D money away from the 230 project! Eliminated within a year or two by AMC.

If you own one of these '72 or earlier Jeeps, I think you want to adapt a Jeep PN 5352620
https://www.rockauto.com/en/moreinfo.ph ... 57&jsn=260
As I recall, this is a normally closed switch; that is, you push the plunger down and it opens the switch. I know the CJ brake pedal has a steel paddle welded to the arm that contacts the button. With the brake pedal at rest, it pushes the switch plunger in and turns off the brake lights.

My '73 had hydraulic switch when I got it; changed it several years to match the above post; used a foreign auto replacement, but don't remember which one. Good solution!

OOPS! I just read through this thread again, and found tgreese's comment about the change to mechanical switches in '73. Now, I remember the spring loaded sliding apparatus that signaled the brake lights. So, my apologies for the above degradation of the hydraulic POS. I did retro-fit a plunger switch as above, but I can't remember whether it was because the original switch quit or because the Hydro-boost system negated the use of the stock switch. Either way, drivers behind can tell when I'm stopping--especially with the third light.