I have done a few of these. It's pretty easy, but there are a few things to think about.
First, depending on the flasher, you can just set the 900 LEDs to "steady" and hook them to the flasher. This should work with almost every existing halogen flasher
built for ambulances. If you desire something other than single flash you can see what the "dwell/on" time is for the flasher and set the LEDs to quad flash (or whatever) and it should work, although I do not recommend this. Sometimes the flasher stays on too long and a second partial flash occurs based on the flash rate of the internal 900 pattern. There is another option to get a "non-single flash" out of the LEDs using the existing flasher. I like to set the 900s to "flash to steady". When scrolling through the patterns the last pattern before steady is this pattern (it is easy to miss). That is a pattern designed for this application and brake lights (really any single pattern remote flasher or triggered to steady application). The lights do a quick flash then then stay on until power is removed. That takes away the problem of the cyclic nature of the other patterns and the dwell time of the flasher causing "extra partial flashes". Every time the flasher activates the LED it will flash then go steady until power is removed by the flash cycle. This is ideal for your application.
Also remember that 900s have a top and bottom section. You have to set both to the same pattern before tying them together. I usually set them to the desired pattern then tie together and cap the pattern and low power wires. Then I tie together the power and grounds leaving a single red and a single black wire from each head. I then tie that directly to the power and ground wires from where the existing halogen was. That is the easiest way to do it by far.
This is the process
- Set each half of the 900 to steady or flash to steady pattern
- Tie together and cap the pattern and low power wires
- Tie together the power and ground on each head (you can add a connector if you want)
- Replace the halogens with the 900 LEDs using the existing power and ground for each light
If you are dead set on some other pattern, 900s don't synch top to bottom or with one another. You would need to replace the ambulance flasher with a LED triple K flasher that has multiple patterns. This is not too hard, and is generally a direct swap out. You still set the 900s to steady but now you can change the pattern on the flasher. There is a little bit of work wiring at the flasher depending on what halogen flasher was there. I rarely do this because the way described above works very well and is far easier.
