I'm going to re-post an older very useful post that inspired me to make an inexpensive wireless brake light indicator to send the braking status of my towed vehicle to the coach driver's cabin in my motor home. The original post is first and my method of accomplishing this follows. If you are a DIYer with a few electrical skills, this is an easy and inexpensive mod. Sorry that none of the original pictures will copy, but you can go back and find this post.
Originally Posted by Bill WA6YBD
WELL!!! I have not have a lot of time to dedicate to this project until I hurt my back several months ago. Been off work ever since and had surgery 3 weeks ago. I had plenty of time after the surgery and actually going crazy with nothing to do. With all this time available I finished the first prototype and want to share it with those who may be interested.
I did not want to design a transmitter and receiver when these things are available from many sources so I purchased a set off eBay for $13.50 from China. There is no way I could build the set for that price.
Next I designed a digital board that could be interfaced with the receiver. What this board does is; it checks to see that there is a signal from the Toad (via the receiver) and also checks that the brakes are being applied in the RV (via the RV brake light switch). There is a green LED for each function. If both green LED's are illuminated everything is OK. Should only one of the green LED's illuminate the board signals the driver by a red LED and also sounds a Sonalert speaker. The transmitter in the car connect directly to the cars brake light switch so anytime the brakes in the toad are being applied the transmitter sends a signal to the receiver in the motor home. So should the brakes be stuck on for whatever reason the transmitter sends a signal. If the motor home brakes are also being applied then the unit is happy. The monitor can be connected to any car and any auxiliary braking system.
Here is a picture of the Receiver unmodified, a picture of my board and a picture of my board installed on the receiver.
Here is a closeup picture of my board installed on the receiver.
Here is a picture of the modified transmitter and receiver mounted in there cases.
I am going to spin the board again to add a switch that will silence the receiver in the event you are not towing. I wish I would have thought of this prior to ordering PC boards... Oh well, live and learn.
I feel this approach to monitoring the braking system is much better then looking in my backup camera to see if I can see the LED bar provided by SMI. Half the time I could not tell if the LED's were illuminated or not. And I almost never looked at the backup camera to see if the brakes were being applied unless I was applying the brakes in the motor home. I do not think I could caught a failure in the event there was one. With the wireless system I feel much more at ease.
Thanks for looking, ~ Bill
Bill, I just completed a wireless brake light transmitter almost exactly like you describe. The TX/RX set is under $5 (shipped) now on EBay with about 20 days delivery time. For the transmitter, I soldered 2 wires to the battery contacts that i obtained by tapping into the existing indicator light that is mounted on the rear view mirror. The transmit button is jammed in the depressed mode by putting a spacer over the button and sliding the locking cover over it (slightly different design on the new version). The transmitter is so tiny on the new model that I was able to velcro it to the back of the towed vehicle rear view mirror and you can't tell it is there from the driver's seat.
In the coach, I purchased a small 12 volt LED brake light made for a motorcycle (about $6 or $7 from China). I have the receiver wired hot from the coach battery (probably less than 50 ma draw). I'm using the the NO contact to switch 12 volts to the light when the receiver is activated. The light is a little bright, but I put it under the dash and it shines down on the floor providing just enough illumination to not be annoying.
It works like a charm and I left the original light bar in the toad rear view mirror for backup in case the wireless system fails. I can always leave the rear view camera on all the time if I need to, but I really prefer to have it in navigation view.
Here is the TX/RX set that I bought for this application:
DC 12v 10A relay 1CH wireless RF Remote Control Switch Transmitter+ Receiver
My total investment with the TX/RX set, light, wiring, wiring taps and solder is about $15.
Thank you for your post. It really inspired me.