Heavy duty light switch operation: how too prevent Burnout
Thread Starter
Former Moderator. RIP Icemark.
Joined: Apr 2001
Posts: 25,896
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From: Rohnert Park CA
Heavy duty light switch operation: how too prevent Burnout
We all know what happens if we don't maintain all the bulb sockets on out cars and allow corrosion to build up. The light switch connector burns out, usually taking the light switch with it.
I have been asked a couple times in the last week on how to help prevent this (besides pulling every bulb on the car and using a little condutive grease/ diaelectric grease on them), so here is a simple way to double or triple the power handling of the circuit and help prevent the switch burn out:
Pretty easy actually.
You’ll need a 12 volt STDM (single throw, dual make) relay from your local radio shack, or car stereo shop (pretty commonly known as a "standard automotive relay"). Any Viper, Python, Sidewinder, Clifford dealer should have it as a DEI P/N 610. Some stereo shops will also call it a Bosch relay (after the company that made the first ones).
Anyway, once you get one it has 5 pins on the bottom, and a drawing on the top or side that lists the pin numbers and what they do. The pin numbers are: 30, 85, 86, 87 and 87a.
In the car at the light switch harness, you’ll need to locate a couple of wires. The Black, a small gauge White/Green and the small gauge Red/Black (18AWG). There is also a larger gauge (about a 14 AWG) Red/Black, you want to ignore that.
Cut the small 18 awg Red/Black. When you do this the parking lights should no longer come on, when you switch on the light switch.
The side of the cut Red/Black that was going towards the switch, needs to hook onto 86 of the relay.
The side of the cut Red/Black that was going towards the car, need to go to 30 of the relay.
The next two wires (the Black and the White/green) will be tapped onto. I recommend soldering, but a good crimp connector will work as well. I do not recommend “T taps” or scotch locks as these type of connectors are very prone to failure, and do not typically have the power handling that you need for this connection. Using the cheaper/easier “T taps” or scotch locks can result in the same melted wiring as you are trying to avoid in the first place.
The wire you tapped onto the black wire, is going to connect to 85 of the relay.
The wire you tapped onto the Wht/Grn is going to connect to 87 of the relay.
87A of the relay is not going to be used.
What this does:
Most automotive relays have at least a 20 ampere power handling rating; however our light switches only have a 10 amp rating so you have effectively doubled or tripled the power handling, as well as you have moved the high current switching of the wires away from the headlight switch and to the heavy duty relay, making the switch much less prone too failure and the load much lighter. Now the switch is really only powering the interior dash lights on the circuit instead of the dash and parking lights. Some people have even reported brighter parking/tail lights.
I have been asked a couple times in the last week on how to help prevent this (besides pulling every bulb on the car and using a little condutive grease/ diaelectric grease on them), so here is a simple way to double or triple the power handling of the circuit and help prevent the switch burn out:
Pretty easy actually.
You’ll need a 12 volt STDM (single throw, dual make) relay from your local radio shack, or car stereo shop (pretty commonly known as a "standard automotive relay"). Any Viper, Python, Sidewinder, Clifford dealer should have it as a DEI P/N 610. Some stereo shops will also call it a Bosch relay (after the company that made the first ones).
Anyway, once you get one it has 5 pins on the bottom, and a drawing on the top or side that lists the pin numbers and what they do. The pin numbers are: 30, 85, 86, 87 and 87a.
In the car at the light switch harness, you’ll need to locate a couple of wires. The Black, a small gauge White/Green and the small gauge Red/Black (18AWG). There is also a larger gauge (about a 14 AWG) Red/Black, you want to ignore that.
Cut the small 18 awg Red/Black. When you do this the parking lights should no longer come on, when you switch on the light switch.
The side of the cut Red/Black that was going towards the switch, needs to hook onto 86 of the relay.
The side of the cut Red/Black that was going towards the car, need to go to 30 of the relay.
The next two wires (the Black and the White/green) will be tapped onto. I recommend soldering, but a good crimp connector will work as well. I do not recommend “T taps” or scotch locks as these type of connectors are very prone to failure, and do not typically have the power handling that you need for this connection. Using the cheaper/easier “T taps” or scotch locks can result in the same melted wiring as you are trying to avoid in the first place.
The wire you tapped onto the black wire, is going to connect to 85 of the relay.
The wire you tapped onto the Wht/Grn is going to connect to 87 of the relay.
87A of the relay is not going to be used.
What this does:
Most automotive relays have at least a 20 ampere power handling rating; however our light switches only have a 10 amp rating so you have effectively doubled or tripled the power handling, as well as you have moved the high current switching of the wires away from the headlight switch and to the heavy duty relay, making the switch much less prone too failure and the load much lighter. Now the switch is really only powering the interior dash lights on the circuit instead of the dash and parking lights. Some people have even reported brighter parking/tail lights.
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IceMark - excellent write up. Thank you for posting that!
One question: Can you clarify which Series this is for. The S4 v. S5 cars have different wiring harneses, therefore the color coding will probably be different as well. Also, for the select few (like me) I have an S4 harness midifed to work with an S5 car. I had to shift some of the pins around.
Thanks again.
One question: Can you clarify which Series this is for. The S4 v. S5 cars have different wiring harneses, therefore the color coding will probably be different as well. Also, for the select few (like me) I have an S4 harness midifed to work with an S5 car. I had to shift some of the pins around.
Thanks again.
Thread Starter
Former Moderator. RIP Icemark.
Joined: Apr 2001
Posts: 25,896
Likes: 24
From: Rohnert Park CA
Wire colors are the same for both S4 and S5 lights, so it will work on either, as well as any other Mazda built before '92 and a couple built after except the Miata and Ford or Kia's built and rebadged as a Mazdas.
Only the pin locations on some of the stock parts are different, but wire colors are the same for the lights.
Only the pin locations on some of the stock parts are different, but wire colors are the same for the lights.
Thread Starter
Former Moderator. RIP Icemark.
Joined: Apr 2001
Posts: 25,896
Likes: 24
From: Rohnert Park CA
Well if your switch contacts are starting to go, then yes your parking lights will be brighter after you add the relay.
As far as the headlights though, the switch already controls a factory relay, so there is no additional brightness to be found unless you clean all the contacts at the headlights and the factory relay.
As far as the headlights though, the switch already controls a factory relay, so there is no additional brightness to be found unless you clean all the contacts at the headlights and the factory relay.
