So... How is that Brake Light Switch Supposed to Work?

**70_Steve** · 07/05/11, 02:44 PM

How can something so simple be such a PIA?

I'm trying really hard to finish up my hydroboost conversion. I still have a little air in the PS fluid, but I'm confident that will work it's way out. What I'm stuck on now is the brake light switch!

I'm trying to do a nice job, so I ordered a Brake Rod Bushing, which looked like it was missing from my original brake system. This bushing fits snuggly inside the large hole in the end of the brake rod from the booster. It also fits snuggly on the pin on the side of the brake pedal. So, when I install it all (nylon washer, open side of brake switch, brake rod w/bushing, closed side of brake switch, nylon bushing, and spring pin) everything fits nice and snug, with no play anywhere, but the brake switch doesn't actuate. To make a long story short, the only way I can make the switch work, is to leave out the brand new brake rod bushing, which puts some slop in the brake rod. That slop seems to be enough to actuate the brake switch.

Somehow, I find it hard to believe that Ford engineered that switch so there had to be slop in the brake rod to work...

What am I missing????

**Viperwolf1** · 07/05/11, 02:48 PM

Yea, it kinda depends on slop to work.

**72Sport** · 07/05/11, 03:25 PM

The spring loaded flat plate in the switch will get bent when someone runs it without the bushing in the rod. When the new owner puts bushing in the rod it won't actuate the switch because it no longer has the necessary travel. If you look at the part of the switch that contacts the rod you will probably notice a slight curve to it. If it is not flat replace the switch.

**bmc69** · 07/05/11, 03:59 PM

Quote:

Originally Posted by Viperwolf1

Yea, it kinda depends on slop to work.

OMFG..can this be true?..

The actuation of the switch depends on the cam action of that flat boss on the pedal end of the actuation rod. its supposed to be perfectly flat against the switch plate when pedal is slack and the slightest relative rotation makes contact occur.

Frankly, I've had all my problems with the stupidly sensitive switch with brake lights that refused to go out.

Pedestrian · 07/05/11, 04:19 PM

Steve, just wanted to make sure you used the Ford end of the brake rod with the flats. The chevy boosters do not have the required flats on the rod end.

I have done some creative bending to repair the switch. They are dirt cheap so usually easier to replace.

**Rockin69er** · 07/05/11, 04:37 PM

I chased this same gremlin for months. Brake lights work.........don't work........work............don't work. I remembered how simple the switch for a 67-72 F-100 was and adapted one of those.

TDubya · 07/05/11, 05:08 PM

My brake light switch went out on my '75 ten years ago. When I replaced it I also intalled the nylon bushing (which it was missing) to take up some of the slop. Brake lights wouldn't work, took out the bushing, lights worked again, been living with brake pedal slop ever since.

**Viperwolf1** · 07/05/11, 05:58 PM

Quote:

Originally Posted by bmc69

OMFG..can this be true?..

I knew there had to be something I didn't know.

**bmc69** · 07/05/11, 06:47 PM

Quote:

Originally Posted by Viperwolf1

I knew there had to be something I didn't know.

I drank a beer to celebrate. Oh...hang on..I'm always drinking one anyways

**70_Steve** · 07/06/11, 11:32 AM

Quote:

Originally Posted by bmc69

I drank a beer to celebrate. Oh...hang on..I'm always drinking one anyways

Celebrating another day above ground!!! I do the same!!!

Quote:

Originally Posted by bmc69

The actuation of the switch depends on the cam action of that flat boss on the pedal end of the actuation rod. its supposed to be perfectly flat against the switch plate when pedal is slack and the slightest relative rotation makes contact occur.

Yeah, I thought about that, but there's nothing to hold the switch in position, so as the pedal moves the cam action of the flats on the brake rod would/should tend to just make the switch rotate and follow the flat on the brake rod. At least that's what I can see.

But then, it was about 125° in my garage when I was laying on my back under the dash with the sweat dripping into my eyes, trying to figure this out.

Oh, and Kurt, I'm using a Superduty H-boost that does have the flat. My setup looks exactly like what Viperwolf1 posted.

Edit:

I looked at the drawing Viperwolf1 posted again, and I do see a difference. My stoplight switch has the connections on the opposite side, and the wiring plug is long since gone. Is that wiring plug, being on the pedal side of the switch, supposed to keep the stoplight switch from rotating? This might make sense if bmc69's theory is correct. Maybe I'll do some playing when I get home!!!

**lonesouth** · 07/06/11, 11:37 AM

I put a piece of felt on the plate to take up the slack between the pedal and plate. Worked enough to sell...

**mrron2u** · 03/31/13, 05:58 PM

God I love this sight! I just did this swap and this page with the picture really helped! It was not easy putting that stupid switch in, but you guys made it easier!