12v DC PWM Relay Help Needed

Old 11-01-17, 11:27 AM
Thread Starter
Join Date: Nov 2017
Location: USA
Posts: 1
Received 0 Votes on 0 Posts
12v DC PWM Relay Help Needed

Hello all!

I'm desperately trying to find a way to elegantly make a vehicle lighting system work. Let me break it down.

I'm adding an LED light that I want to be activated by the dome light in my car. I also want to be able to switch it on using a aux switch that has an LED indicator, independently of the dome.

This usually wouldnt be too hard, but it's a Toyota that uses negative PWM switching. So I must tap into the negative wire of the factory dome light. And because it's PWM when it fades on/off (not PWM when it's totally on, just during fade on/off) a standard Bosch style relay doesn't work well as it rattles with the frequency of the pulse and won't last long.

What I've determined is that I need a SSR that can then be piggybacked with a mechanical relay for the aux switch. I've managed to get this to work using one of the big box style SSR with the 4 terminals switched by the (-) of the factory dome then piggybacked to a Bosch style relay which is (+) switched by a rocker switch. The issue is that it's a very ugly setup.

I'm hoping to find something cleaner. Does anyone know if something like this would work?

Phidget VINT 4 Isolated Solid State Relay Module - RobotShop

I realize it's 4 isolated relays and I would only need two, but if it would work, I wouldn't care about the other relays not being used. I guess the question is: with the relay I posted, can I wire it to be switched from the (-) PWM source of my car and also wire it to be (+) switched from a aux rocker switch. If not, does anyone know of an alternative?

I really appreciate your help with this! P.S the light is about 8amps.​​​​​

Thread Tools
Search this Thread
Ask a Question
Question Title:
Your question will be posted in: