new here. question on 71 jeepster commando brake light presure switch. tail lights stuck on

natejones75

Gear Grinder
Apr 20, 2024
7
fairfield, illinois
First Name
Nathan
Willys Model
  1. Jeepster
Willys Year:
  1. Other
71 jeepster, has the break light oressure switch under the master cylinder. I replaced this switch about 3 years ago

started finding a dead battery every time i went to use the jeepster. Fou d out the tail lights are dimly staying on all the time, even after shitting it off and parking it. tracked ot back to this pressure switch. unplug one of the wires and the lights go off. What causes this? ive put a cardboard divider between the two wires to unsure they werent touching but it is still happening. Any thoughts? i have also noticed a little.smoke coming from one of the wires occassionally
 
Welcome to OWF Nate!
If you are not concerned about originality, consider substituting a generic mechanical brake light activator like this one (at least that way you can wait until you've absolutely got to crack open what is probably an otherwise hydraulically-functional system):

1713664983736.png


The lever on this switch feels for the position of your brake petal arm. You just have to come up with a way of mounting it somewhere.


Smokey wiring is trouble. You'd be moving the two connections from the hydraulic switch to the ones on this switch. Check those leads for compromised insulation.

Only You can prevent Jeepster fires.
 

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Joe B said:
Only You can prevent Jeepster fires.
Click to expand...
Yeah I 100% agree.

Not a ton of fusing on stuff at times and either way a slow burn of wiring below a fuse rating could really cause a major fire.

Check your free play on the rod to the Master Cylinder, maybe it's pushing on the MC and is enough to create the small pressure needed.

They make a high and low pressure switch from what I recall, if the MC happens to have a residual pressure valve it might be above the rating of the switch.

They can really be a pain to deal with. I like the plan to swap to a mechanical pedal operated.
 
Joe B said:
Welcome to OWF Nate!
If you are not concerned about originality, consider substituting a generic mechanical brake light activator like this one (at least that way you can wait until you've absolutely got to crack open what is probably an otherwise hydraulically-functional system):

View attachment 162879


The lever on this switch feels for the position of your brake petal arm. You just have to come up with a way of mounting it somewhere.


Smokey wiring is trouble. You'd be moving the two connections from the hydraulic switch to the ones on this switch. Check those leads for compromised insulation.

Only You can prevent Jeepster fires.
Click to expand...
Should not that switch be N/O and closes when pedal pressure is applied?
 
Excellent point Todd!
The switch shown above would need to be mounted in such a way that the arm of the "resting" brake petal will be normally pushing on it and forcing the state to "Normally Open". When you hit the brakes, the pressure on the spring-loaded switch lever is released allowing the contacts in the switch to close and light the brake lights.

I suspect that it is set up this way so that if the switch were to come loose from its mounting, the brake lights would be "stuck on", which is a slightly safer condition than the brake lights (unknown to the operator) never coming on.

Nate,
If you've got a multimeter, set it to ohms resistance and see if the existing hydraulic switch -- with the two wiring harness wires disconnected -- shows a resistance across it.


Jeeps -- and nearly all cars from the good old days -- suffered the consequences of owners adding stereos, CBs and lighting systems.

Guys tapped power for these accessories off of wiring harnesses using diabolically "creative" methods.

Working under the dash is a drag, but spend the time to take a good look under there and remove any remnants that might still exist from any of that stuff, and protect any resulting exposed conductors in the original harness.

Wiring that has generated smoke is usually pretty easy to spot. I've used my cellphone camera set to video with the "flash" switched on to "blindly" record a view from below a dash. This can help you get a feel for the general condition of what's up under there before you might have to resort to the yoga positions to undertake any needed repairs.

Here's an example:
 
A faulty brake switch (not uncommon on these jeeps) can possibly cause both problems. In your case, it appears that the switch is "kind of" making contact when it should not make contact at all, a hi-resistance connection. Probably a weak spring in the switch or the contact disc isn't in the correct position due to wear. This in turn can send enough "power" to the tail ligths to barely glow, but not really light up, but over time it can heat the wires, especialy at corroded connections, resulting in "a little smoke". If you have an ohm meter ( I prefer analog for this stuff, but digital is fine) unplug and measure the resistance (after unplugging both wires) between the two switch terminals. It should be "infinite". When you step on the brakes it should be "zero". If either measurment is not correct the switch is faulty. If you're fast, you can replace it without having to bleed the brakes. The switches are cheap, so cheap that i question their quality. The last time I found them in what seemed to be good quality was at Rockauto, made in Mexico.

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Last edited:
Follow up: Thanks for all the replies. Sorry for the late reply.from me. With the jeepster off and wires unhooked, im showing an ohm resistence reading of about 13.1 across the two terminals of the switch. Just a bad switch?
 
natejones75 said:
Follow up: Thanks for all the replies. Sorry for the late reply.from me. With the jeepster off and wires unhooked, im showing an ohm resistence reading of about 13.1 across the two terminals of the switch. Just a bad switch?
Click to expand...
Yep... That's a start. These are known to go bad, hence the sale of replacements. Some stay good for decades, some last a month :(
 
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