Brake Light Switch Relay

[jonclancy]

I was enjoying a razzz out to Bibury with Madame, when a fellow motorist let me know my brake lights were not working.

"Not sure I use the brakes that much!" was my initial thought. These are light cars, after all. But he was right. Tickle the brake pedal = no lights. Late in the braking zone style braking and they worked.

Googling showed I was not alone. The hydraulic switch on our cars is a flawed design. The trouble is the contacts in the modern switches appear to be a bit less meaty than those of yesteryear. They just don't like the full amperes going through them. There is probably a spark each time you brake that reduces the switch life.

Options are:

Fit a pedal-actuated switch.
Fit LED bulbs.
Fit a Relay.

I'm going with #2 and #3.

Plus, googling pointed me at the better-quality Hella switches.

Now my Spag Bol is ready, I will have to leave you all in suspense... for a little while!

[jonclancy]

I found a suitably-rated automotive Relay for under three quid delivered.

12V Automotive Changeover Relay 40A 5-Pin SPDT with Socket

eBay link: http://r.ebay.com/LYuWzd

I've attached a pic of the Relay in question, and of the wiring diagram/Pinout.

More of that later...

[jonclancy]

Thanks to those who provided the images.

Now, how does this all work?

On the car, the brake switch connects the 12v feed to the bulbs. Simples.

On the Relay, the coil is energised by making the switch, thus pulling in the contacts and feeding 12v to the bulbs.

Spookily similar, but uses a fraction of the current to energise the coil. So your switch should last much longer (years longer, hopefully!), and you won't risk getting shunted in traffic.

A couple of chaps have posted excellent articles on this subject...

Dave DuBois

http://userwebs.donobi.net/sufuelpumps/ ... _Relay.pdf

Cosmo

http://www.jalopyjournal.com/forum/thre ... ts.798760/

... and a ton of stuff on the MG and Westfield forums.

I suspect you will have an M10 brake switch. I looked in my very early build manual, and listed were the items in the brake kit. This info appears to be missing from the later manual.

I found the Hella online catalogue, and found the brake switch on Amazon for under six quid delivered. It's gone up to £14 now!

HELLA 6DL 003 262-001 Brake Light Switch

http://cat.hella.com/web/public/hasa/en ... D8FDCF909B

I also treated myself to a Draper ratchet crimp tool and a decent selection of terminals.

How am I going to put this lot together!

[jonclancy]

I'm going to use my switch to make the ground connection.

Remove the female connectors from the switch. One will be 12v feed, the other goes off to the lights.

The feed will enter the Relay and also feed the coil. Crimp two wires on the Relay holder (30/86) into one male terminal.

Crimp a female terminal onto 85. Crimp a male terminal onto 87 (output to lights).

The coil ground (85) pushes on to one side of your switch. Make up a ground lead from the other side of the switch.

Hot feed (green) connects to the twin wires in the male terminal. Relay output (87) connects to lights (green/purple).

That's pretty much it.

Most will find this a no-brainer. But hopefully this will be of some use. As there are so many stories of the switches failing, I'm surprised that a Relay isn't fitted as standard equipment.

I'll let you know how I get on following my own instructions!

PS use a crimp tool, not soldering iron! But you all know that...

[Westfield 129]

Seems like a lot of trouble. My brake line switch has been in the car for more than 30 years, and it works fine. No relay. One isn't necessary. Really.

The car is simple. A quick pass with the volt meter will find the problem in a minute, starting with the switch, then the rear connector plug.

I have had brake light failure, but it was the connection at the large connector plug at the back of the car, or the ground. A couple of times, it was the socket as it was corroded. I have since replaced the plugs and pins with new ones when I rewired the car, and have not had a problem in over a decade. I used the old brake switch. It's still in the car.

I'd just put a new switch into the brake fitting, and be done with it. Those switches have never been a problem in any car that I have owned, even the British ones.
I could understand putting a relay on the headlights if you had switched to halogens, or put a relay on the fuel pump to help isolate it from the tach. But a relay on a momentary switch seems like overkill and another point of failure.

So far, I have had my fuel pump relay fail. That's perhaps the only electrical failure that I have experienced since I have rewired the car.

What's wrong with soldering connections? I often silver solder terminals. However, for the most part, I too use a ratchet crimper and precise dies that match my insulated or non insulated solderless terminals.

[jonclancy]

Hi Jan,

The evidence out there suggests otherwise. The quality of many modern switches available to us here in the U.K. appears poor. This is an easy and safety-related mod; I'm content mitigating a risk.

ETA. Solder joints can fail with vibration. Crimped far better in some circumstances.

[jonclancy]

Update:

I have installed my new switch, changed the brake fluid, and connected the relay.

All works as it should, and is neat.

The downside is my new LED bulbs don't properly fit, so I'll be calling the supplier for advice after Easter. I also need to free off my rear brake adjusters with my new 5/8" square spanner and some blowtorch action. Once these two things are done, that's the project successfully completed.

[Simon Marks]

Hi, Jon,

I've heard that some of the bulb holders (the Westfield supplied "beehive" ones, I think) are set up for the two pins to be directly opposite each other. Most bulbs come with the pins slightly offset and it can be this mismatch that causes the fit problems. Lucas codes LLB 380/381 (http://www.lucaselectrical.co.uk/downlo ... alogue.pdf). Might be worth a look to see if this is the issue?

Simon

[jonclancy]

Hi Simon,

Both my old and new bulbs are offset. The bottom contacts are very slightly different.

My replacement Lucas base plates are set up for both types, I believe...

I'll call next week to see what I am doing wrong!!