Brake Switch, electrical research

This weekend was possibly the most beautiful 2-day weekend we've had in the Pacific NorthWest since the middle of last Fall. We had mostly clear skies with temps in the mid 60's on Saturday and into the low 70's on Sunday. It was perfect be-outside weather, so that's exactly how it was spent. Today, I'll talk about the brake switch installation I did on Saturday, and flap a bit about how the rest of the weekend was spent. Last, and certainly not least, my good friend from Kentucky (Andy) forwarded to me the net result of 9 months of researching circuits for the ALH TDI engine. Great stuff.

Brake Switch
In the bracket that holds the accelerator pedal to the VW NewBeetle, there is also a switch that is activated by the movement of the brake pedal. Recognizing that VW wouldn't put in a washer if they felt they could get away with it, we have to assume it has a purpose. It does, but not much of one for my implementation. First, the pedal switch turns off the cruise control. This is for safety, I believe. Second, the ECU (car computer) compares the signal from that switch with the other (and the brake lights) to see if there is a problem in the lighting. For my purpose, though, if there isn't a signal that acts like a brake switch, the ECU throws a code, and the check engine light pops on.

Fake it or Make it
There are 2 ways to handle the brake switch in a conversion. Many of the vanagon conversions have wired into the master cylinder switch and trigger the brake switch signal via a relay and a variable resistor to get the singal voltage right. I call this a "fake", but it seems to work very well for those that have done it. I actually got a switch from the donor car, so I figured I'd try fabricating a switch bracket and put it under the floor pan where the accelerator rheostat is. The picture to the right here shows where.

Clamp, Test, and Go
I took a short strip (less than 6 inches long, about an inch wide) or galvanized sheet steel that I had laying around from the radiator work. I got under the bus with the switch in hand and found a spot that allowed for the switch to open and close with the pedal motion when I held the switch against the lever. The switch button is activated / deactivated by pressing against the floor. I cut the mounting bit off of the old donor bracket, and pop-riveted it to the strip of steel. I then bend the strip of steel into an old-style capital "C" shape with little wings sticking out the end. I was able to get the clamp around the brake lever so the wings were about 3/8" apart. I removed it, drilled a couple of pilot holes, re-installed it and tightened the ends together with sheet metal screws. The clamp and the switch don't budge, and they will be covered by the same belly pan that will be covering the accelerator rheostat, so it should be weather-safe. Now, the switch opens and closes when the pedal is pressed and released - just like the donor car.

Present in the Mail
If you have followed my thread on the TDIClub, I have been anticipating a packet from one of the members there (AndyBees) containing the wiring diagram research he did for his vanagon TDI conversion project. His donor engine is from a 2002 Jetta, so much of the wiring is the same as my 1998 New Beetle donor. This significantly reduces the amount of time I will have to spend trying to figure things out. It doesn't completely eliminate my research though because there are some differences between these 2 configurations. For example, the 1998 New Beetle did not have an immobilizer, so I don't need to use the ignition key from my donor engine. Andy will have to. The circuit that deals with the starter is therefore different between our engines. And so it begins. I have barely started reading through his drawings and notes. I had some of the drawings in my Bentley for my Jetta, but his hand notes will prove to be very useful. Now, to find a wiring diagram for a 1998 New Beetle TDI without having to buy the $80 book.....

Weekend Fun
So, I did the brake switch over the course of a few hours Saturday afternoon. I spent the morning first at T's lacrosse game and the helping build raised garden beds at my kids' school. The evening was spent playing with C and reading Andy's notes. Sunday morning we skipped church to work in the yard. It was the first mow of the season, so there's the whole tune-up of the mower first. The grass looks terrible, but at least its shorter, and we were able to enjoy a picnic lunch on it. C had a lacrosse game too, so we all watched him play and then went out for ice cream. Overall, it was a great weekend with a great balance of volunteering, housework, kid time and a little project work on the old bus.

up next...
ALT belt, battery isolator, camping battery install, main battery install and, hopefully, wiring up the primary electrical (ALT-starter-battery).

pictures:
top - brake switch installed with the accelerator rheostat for positional clarity
bottom - close-up of the brake switch. Hard to tell how the action works. I'll take another one from more off the side so its more obvious.