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Old 01-01-2013, 06:28 PM
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Universal Stop Light Switch Wiring

I put one of these Universal Stop Light Switches on my hotrod. It originaly had an inline pressure switch. I eliminated it and extended the wiring up to the Universal Stop Light Switch as seen in the picture.

It worked perfectly for about 8 months....but today while doing other work on the car I smelled something burning and smoke was coming from the area where the wiring hooked to the Universal Stop Light Switch.

I disconnected the battery and of course the smoke and smell disappered.

I unplugged the two wires to the switch and hooked the battery back up with the wires unplugged from the switch and the wires showed no evidence of heat or smoke.

I hooked the wires to the switch and connected the battery back up and the wires were getting warm again, so I unplugged them.

This switch says it is rated at 42 Amp max. What does that actually mean? Did I do something wrong by just extending the wires from the pressure switch to the front of the vehicle and plug them into this Universal Switch?

OR....is it a defective China made switch and I can just replace the switch and everything will be OK?


I thank you in advance for your input on this subject.
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Old 01-01-2013, 07:02 PM
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The chances are slim the problem is in the switch. Disconnect the switch and using a test light or ohm meter, see if you get continuity from either terminal to ground. If so the switch is bad. If not the trouble can not be in the switch. If the switch was shorted your brake lights would just come on. It the switch is not shorted the problem must be beyond the switch.

John L
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Old 01-01-2013, 07:43 PM
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fuse

The first and most important issue is a fuse should have blown which would protect the wiring in this type of failure.
A test of the switch can be done with an ohmmeter. With the wires disconnected, test each of the two terminals with respect to ground. You should have no resistance reading on either terminal.
Also a short to ground could be occurring somewhere else in the circuit. But it seems like the switch is the problem.
The 42 amp rating is the capacity of the switch contacts to handle current up to 42 amps without damage. Not an issue in this situation.

vicrod
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Old 01-01-2013, 08:07 PM
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Quote:
Originally Posted by John long View Post
The chances are slim the problem is in the switch. Disconnect the switch and using a test light or ohm meter, see if you get continuity from either terminal to ground. If so the switch is bad. If not the trouble can not be in the switch. If the switch was shorted your brake lights would just come on. It the switch is not shorted the problem must be beyond the switch.

John L
The first thing I noticed and forgot to mention was that the brake lights were on....and I walked to the front of the car and pulled up the hood and saw smoke.

I'll check the switch tomorrow.


Thanks
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Old 01-01-2013, 08:25 PM
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Quote:
Originally Posted by Sweet-34 View Post
The first thing I noticed and forgot to mention was that the brake lights were on....and I walked to the front of the car and pulled up the hood and saw smoke.

I'll check the switch tomorrow.


Thanks
The universal switch is mechanical so it could be shorted or out of adjustment and getting hot do to being on so long. I think you are on the right track.

John
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Old 01-02-2013, 02:59 AM
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My vote is the switch, the others have given sounds advice, fuse should have blown before the wires got hot enough to smoke......... try putting just a hi amp toggle in place of the brake switch, for testing only, and see if you still have warm wires etc......
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Old 01-02-2013, 07:44 AM
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Fuses

Quote:
Originally Posted by vicrod View Post
The first and most important issue is a fuse should have blown which would protect the wiring in this type of failure.
A test of the switch can be done with an ohmmeter. With the wires disconnected, test each of the two terminals with respect to ground. You should have no resistance reading on either terminal.
Also a short to ground could be occurring somewhere else in the circuit. But it seems like the switch is the problem.
The 42 amp rating is the capacity of the switch contacts to handle current up to 42 amps without damage. Not an issue in this situation.

vicrod
All fuses are 30 Amp. What fuse amp should be used for:

Headlights/Tailights

Brakelights

Engine Cooling Fan

4-Ways

I used a Continuity Tester and it showed continuity in the off position and no continuity in the on position. I touched one pole with one end wire from tester and the other pole with the other end of the tester. Am I doing it right....or should I be touching the lead of the continuity tester to a good ground (steel brakeline) and touch each terminal on the switch and see if I get a reading?

I used a Test Light and grounded it to a steel brakeline and it showed nothing when I touched each post on the switch.

All comments welcomed.

Last edited by Sweet-34; 01-02-2013 at 07:59 AM.
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Old 01-02-2013, 09:47 AM
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Headlight and fans, use a relay.

Basic fuse requirements (from Painless wiring):

Cigarette Lighter……………………………………………….20
Headlight Switch……………………………………………….30
Emergency Flashers………………………………………….15
Turn Signals………………………………………………………15
Gauges………………………………………………………………10
AC/Heat Relay…………………………………………………….5
Radio (Constant)……………………………………………….10
Horn…………………………………………………………………..20
Door Lock…………………………………………………………..20
Wipers………………………………………………………………..15
Brake Switch………………………………………………………20
Dome/Trunk……………………………………………………….10
Electric Fan Relay………………………………………………..5
Power Antenna……………………………………………………10
Power Windows…………………………………………………..20
Electric Fuel Pump………………………………………………15
Coil……………………………………………………………………...30
Radio Ignition (Switched)……………………………………10
Backup/Cruise Control…………………………………………10

The fuse requirement and wire gauge has to take the accessory load into consideration. Using too small of a wire can let a wire burn even though the accessory load matches the fuse rating. Using too 'big' of a fuse can let a wire burn even if the wire gauge matches the load.

Testing:

Set the meter to the 20 VDC volt scale (or whatever is close to that). Ground the neg. meter lead, then probe the wires separately. In the "at rest" position- brakes not depressed, there should be power IN but not OUT.

With the brakes depressed there should be power at BOTH terminals.

If there is no power IN, the wire has burned or the fuse blown, or the wire has been disconnected.

If there's power IN to the switch but nothing OUT with the switch activated, you have a bad switch.

You can also test the switch using the ohm setting, be sure to disconnect the switch from the wiring first. Connect the meter leads, one lead to each terminal. If the switch is OK, you should have continuity (close to zero) with the switch activated (brakes ON), and infinity with the switch at rest.

If you have a high ohm reading w/the brakes ON, or infinity, the switch is no good.

Last edited by cobalt327; 01-02-2013 at 10:02 AM.
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Old 01-02-2013, 11:04 AM
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Quote:
Originally Posted by cobalt327 View Post
Headlight and fans, use a relay.

Basic fuse requirements (from Painless wiring):

Cigarette Lighter……………………………………………….20
Headlight Switch……………………………………………….30
Emergency Flashers………………………………………….15
Turn Signals………………………………………………………15
Gauges………………………………………………………………10
AC/Heat Relay…………………………………………………….5
Radio (Constant)……………………………………………….10
Horn…………………………………………………………………..20
Door Lock…………………………………………………………..20
Wipers………………………………………………………………..15
Brake Switch………………………………………………………20
Dome/Trunk……………………………………………………….10
Electric Fan Relay………………………………………………..5
Power Antenna……………………………………………………10
Power Windows…………………………………………………..20
Electric Fuel Pump………………………………………………15
Coil……………………………………………………………………...30
Radio Ignition (Switched)……………………………………10
Backup/Cruise Control…………………………………………10

The fuse requirement and wire gauge has to take the accessory load into consideration. Using too small of a wire can let a wire burn even though the accessory load matches the fuse rating. Using too 'big' of a fuse can let a wire burn even if the wire gauge matches the load.

Testing:

Set the meter to the 20 VDC volt scale (or whatever is close to that). Ground the neg. meter lead, then probe the wires separately. In the "at rest" position- brakes not depressed, there should be power IN but not OUT.

With the brakes depressed there should be power at BOTH terminals.

If there is no power IN, the wire has burned or the fuse blown, or the wire has been disconnected.

If there's power IN to the switch but nothing OUT with the switch activated, you have a bad switch.

You can also test the switch using the ohm setting, be sure to disconnect the switch from the wiring first. Connect the meter leads, one lead to each terminal. If the switch is OK, you should have continuity (close to zero) with the switch activated (brakes ON), and infinity with the switch at rest.

If you have a high ohm reading w/the brakes ON, or infinity, the switch is no good.
Thank you so much for taking the time to help me with my problem. I will post when I solve the issue.
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Old 01-05-2013, 09:23 AM
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Problem Solved!!!

The switch had shorted out causing an overload on the wiring. The Brake Switch had a 30 amp fuse in it and that is why it didn't blow the fuse.

I replaced the 30 amp with a 20 amp as Painless Wiring suggested. All is well.......no more heat/smoke and the new switch works perfectly.

I already had a disconnect for the battery installed but was working on the car (start/run) when this happened.

From now on......I'll never park any of my cars for any period of time without diconncecting the batteries. Could of burned my house down if it would have happened in the middle of the night.

I would suggest to everyone to install a quick battery disconnect. You just never know!!!


Thanks to everyone for your help!!!!!!!
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Old 01-05-2013, 04:55 PM
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Good to hear you got it fixed
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Old 01-06-2013, 01:45 PM
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more to the point

Good to hear you found the problem.
The battery disconnect does not help you when you are using the car. Although it is good for storage or a safety disconnect.
More importantly, all circuits must be fused properly.
This includes the main accessory wire from the battery that needs a fuse link or a maxi fuse.

All viewers of this thread, be advised.

vicrod
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