Rebody How can we fool the speedo signal wire?

[Pingu]

My wipers on the kitcar only work as if the car is stationary.

Intermittent wipe only.

The instrument cluster has been removed and replaced with other instruments. The speedo signal wire (SW/WS) (Black / White) is disconnected.

My first thought was that if I supplied this wire with 12v, or shorted it to earth, the speed reactive stuff would react. So I tested the wire on my blue car (standard M Roadster). The wire is 0.31v when everything is switched off, 11.28v when the ignition is on, but engine off, and seems to follow the alternator, but with a reduced voltage when the engine is on. The voltage is not any different when the car is in gear and the speedo thinks the car is moving.

To test the wire, I disconnected the driveshafts and ran the car in gear.

The wipers change from intermittent to normal speed at around 5mph. The voltage on the SW/WS wire makes not significant jumps or variations.

My conclusion is that this wire is a CANBUS-type signal wire, and can't be fooled in the normal electrical ways.


Does anyone have any ideas how I can make my wipers behave normally?

One option is to bypass the complete Wash/Wipe module, but I don't really want to do that.

 

[Foglem]

CAN bus requires 2 wires, so I think you have something else going on there.

I believe the "speed" sensor runs to the rear differential. My guess, it is a hall effect style sensor (generates a pulse when metal gets close to it) that counts gear teeth.

I have a manual I can run through tonight and see if it has any useful information.

The idea here is that the wipers behave based on the Speedometer input? I'll start doing some research. I have to do this anyway because my wipers are no longer reacting to the stalk.

 

[Stevo7682]

There will be some link to something that registers the cars movement as all 3 my zeds return to intermittent wipe if stalk at normal speed and you stop at lights etc then when drive off they return to normal speed.

So l looking at the wiring diagram i have the wash wipe module is the heart of the system there is a black/white wire says vehicle speed signal ( an input into wash wipe module terminal 5 ) when you run back it takes you to a junction with obc ( sw/ws black / white terminal 13 obc) from there runs back to the dash clock still as a output from terminal b2
Dash must have an input for this signal ( for speedo to work ) could be possible to wire wiper module speed signal to the dash input for speedo.
Stephen.

Gary how does your speedo currently work.

 

[Pingu]

Gary how does your speedo currently work.

Speedo works using the signal from the Hall effect sensor on the diff. I needed to drive an exact mile to calibrate it. There is no wire from my speedo that exports a speed signal from the speedo.


I thought the BMW worked like this...

Hall effect wire alternating current signal goes into the speedo and the speedo converts this into a reading on the dial.
When the speedo gets to a certain speed the speedo output wire (BLACK / WHITE) would either switch to 12v, or switch to Earth.

If it worked like that, I could make something that would change the wiper speed when the speedo signal changed.

The problem is, when the speedo gets to 5mph, the speedo signal doesn't seem to change significantly, but the wiper speed does.




I've just had an idea . I wonder if the seemingly insignificant change is enough to trigger the transistor in the wash/wipe module.

Originally, I was looking for a change from 0v to 12v, or a short to Earth. I think I will take another look and actually measure the speedo reading and the voltage at different speeds. I just assumed the voltage was rising because the alternator was charging. The engine hadn't been revved, so the alternator had never got to 13.5v, so it was still in the revs/voltage=proportional phase.

The driveshafts are disconnected, so there will be no problems with the ABS if I go above 30mph. (If you go above 30mph without the front wheels turning, the ABS has a brain fart and the speedo goes to zero.)

 

[jaguartvr]

Strange one, I haven't heard of any other builder reporting this problem. On the California the wiper motor is replaced with a Lucas wiper motor but still relies on the existing wiring and wiper switch.
Could you have a faulty wiper motor? Could be worth trying to swap it out, I'm sure Spurs would have one in stock.

 

[Pingu]

Strange one, I haven't heard of any other builder reporting this problem. On the California the wiper motor is replaced with a Lucas wiper motor but still relies on the existing wiring and wiper switch.
Could you have a faulty wiper motor? Could be worth trying to swap it out, I'm sure Spurs would have one in stock.

The first test will be to send 12v to the wiper motor and see what happens. I'm guessing it will go at fast speed.

There are two +ve wires going to the motor and a -ve. The second +ve wire could either be the half (or normal) speed wire or it could be a "park" wire.

My first port of call is to study the speed wire from the cluster on my blue M.