Brake Light Switch, Again?

[wazzz]

This beautiful schematic cannot be applied to rokemester's car. Yours is an older system with two SPDT switches (3 contacts). Rokemester's car is a 3.2 which uses SPST switches (only 2 contacts).

Also, rokemester, I didn't dig into Sal's schematic in details, but I noticed one thing. You need to reverse 85 and 86 in his schematic, as your relay contains a diode that compels this mode. Sal's relay didn't contain a diode, so it didn't matter which way the coil was connected.

[rokemester]

Thanks! I’ll report back. I tested the new brake light switches this morning with the stock wiring and they are both operational.

[Cloggie]

Originally Posted by wazzz

This beautiful schematic cannot be applied to rokemester's car. Yours is an older system with two SPDT switches (3 contacts). Rokemester's car is a 3.2 which uses SPST switches (only 2 contacts).

Also, rokemester, I didn't dig into Sal's schematic in details, but I noticed one thing. You need to reverse 85 and 86 in his schematic, as your relay contains a diode that compels this mode. Sal's relay didn't contain a diode, so it didn't matter which way the coil was connected.

Oops, I forgot to mention that this is as installed on my '89 Carrera restomod.

There is a bit of wiring to do for sure....

Since I have had a number of those switches fail and need to be replaced, I just said **** it and get the 3 pole ones from Germany - they last.

The Brazilian and Malaysian ones fail within a few months....

D.

[rokemester]

The switches I replaced were German and they were on the car when I bought it over 10 years ago.

[rokemester]

Originally Posted by wazzz

This beautiful schematic cannot be applied to rokemester's car. Yours is an older system with two SPDT switches (3 contacts). Rokemester's car is a 3.2 which uses SPST switches (only 2 contacts).

Also, rokemester, I didn't dig into Sal's schematic in details, but I noticed one thing. You need to reverse 85 and 86 in his schematic, as your relay contains a diode that compels this mode. Sal's relay didn't contain a diode, so it didn't matter which way the coil was connected.

So do I need to source a different relay? My relay with a diode won’t work?

[rokemester]

Originally Posted by scarceller

It's a standard SPDT automotive Relay. They use these for Fog lights and alarms. Here's one on ebay 1 Pack Car Truck 12V 12 Volt DC 40A Relay & Socket SPDT 5P 5 Wire Replace | eBay.

Very simple install and works great, it really saves your switches from arching out.

Sal, the link in this post is dead. Will this relay do the job? Bottom line it appears the Painless brake light relay kit is a no go. I liked that it had a bracket mount option.

https://www.ebay.com/itm/115804829139

[wazzz]

Originally Posted by rokemester

So do I need to source a different relay? My relay with a diode won’t work?

Yes it will, but you need to make sure you wire it with the right polarity. While the relay used by Sal didn't have this diode inside and so it could be wired in any polarity.

This diode is useless in this application, but it does no harm provided that you stick to the correct polarity.

The correct polarity in your case means swapping 85 and 86 in Sal's diagram if you decide to follow it.

[rokemester]

Thanks! I’ll give it a go. Meanwhile I have a SPDT relay on its way.

[rokemester]

I installed a 5 wire relay today following Sal’s schematic. No brake lights. I was feeling good! Thought I was following the schematic and understanding the circuit flow. I guess not! Clearly I’m electrically challenged. A single pole single throw SPST would have been a better option?





30 - red wire to black green of harness
87 - blue wire to black yellow of harness (brake lights)
86 - white wire to brake switches
85 - black wire to ground and to brake switches
87a - yellow wire not connected

[scarceller]

First question before you attempt to wire up the relay.
Unplug a connector from an existing switch on the master cyl.
Then jumper across the 2 pins in the connector with piece of wire.
The brake lights MUST come on.

Please verify this step before you proceed with the relay install.

The relay you have with diode will work, but first do above test.

Also we are assuming the current switches in the MC are in working order? Those also MUST be sanity checked with a ohm meter to be sure they close and make contact with foot on brake. The relay solution simply limits the amount of current through the stock switches, they must be in working condition.

And with your relay you MUST swap 85 and 86, basically 86 gets 12vdc not 85. If you wire it up wrong with pin 85 getting power you cause a short across the diode and the diode will likely blow out.
To test the relay to be sure it's still good simply hot wire 12v to pin 86 and then ground pin 85, you will hear and feel the relay click closed. You can do this test by connecting directly to battery posts or any good 12 volt source.

[rokemester]

I have confirmed.





I installed new MC switches and confirmed they both work plugging them into each plug individually. I moved off the relay with the diode. I wired up this SPDT 5 wire relay.

[rokemester]

This relay with yellow not connected. Tested the diode relay and I can hear it click when tested.

[scarceller]

This relay has NO diode, correct? You can prove this by applying power across 85 and 86 in both directions. 85-12v and 86-ground then swap them if the relay clicks closed in both cases it has no diode.

Originally Posted by rokemester

This relay with yellow not connected. Tested the diode relay and I can hear it click when tested.

[rokemester]

Sorry I’ve tried two relays. One with a diode and the most recent relay, no diode.

[scarceller]

Please verify the new recent one has no diode. And let's stick to using the relay without a diode.

Once you verify it has no diode we can proceed

Originally Posted by rokemester

Sorry I’ve tried two relays. One with a diode and the most recent relay, no diode.

[rokemester]

Will do! Thank you!
Relay only clicks with power to white 86. The relay I assumed had no diode.

[scarceller]

Originally Posted by rokemester

Will do! Thank you!
Relay only clicks with power to white 86. The relay I assumed had no diode.

OK, so pin 30 and 86 needs to have 12vdc, can you verify that you have those 2 pins both connected to 12vdc. That's step #1

Then when the relay is not connected to anything verify if pin 30 is normally closed to pin 87a or 87? You need a ohm meter to test this. Measure for continuity between 30 and 87a and also 30 and 87. Which one shows 0ohms?

The relay you have without the diode has me confused looking at the picture on the top of relay, it looks like 30 to 87 is normally closed? We need to confirm this.

[rokemester]

Sal, thank you for walking me through this! I will confirm. My wife has me on house cleaning duty for her next couple of hours. Will check back soon.

[scarceller]

Also, on the existing plug that you removed from the switch on the MC verify with a meter which of the 2 pins has 12vdc on it. Once you know what pin that is mark that connector with a red marker on the pin. That pin is your power pin the other pin goes to the brake lights.
You need to be certain what pin is the power pin on the white connector that you unplugged from the switch on the MC.
Unplug BOTH MC switches and leave them both unplugged.

[rokemester]

Roger that! I examined the connector carefully previously for black green (fused 12v) and black yellow connection (to brake lights). Will confirm.