Fan indicator questions - Fuel Economy, Hypermiling, EcoModding News and Forum

QuickLTD · 05-18-2009, 10:00 PM

I have been reading about "cooling fan indicator lights" so I purchased two 12V lights in an appropriate size (green in color)to mount in my dashboard. Two because I have two speed fans. One for each speed. I do all my own work and always have but I am a bit rusty in automotive electrics. According to the Fan Circuit diagram I have included in this post am I correct that "87" is the correct pin on each relay to tap into?

Does anyone have a better idea than what I was thinking?

I did a few searches and came up with info but not what I was looking for.

Thanks,
Dean

The Atomic Ass · 05-18-2009, 10:03 PM

I would say yes.

Daox · 05-18-2009, 10:37 PM

Yup, thats exactly what I did with mine. Works like a charm.

Deezler · 05-20-2009, 12:59 PM

Yeah I gotta do this too, as the weather heats up and coolant temps become critical.

Without high-jacking the thread, is the basic premise that you just squeeze an extra wire or pin into the 87 terminal on the coolant fan relays? Extra power draw of an LED is negligible I suppose. Should one fuse the newly tapped wire in case of a short?

QuickLTD · 05-20-2009, 06:38 PM

In my situation yes. Some relays have a fifth terminal that can be used for indicator lights or whatever. I didnt go with an LED because I am unfamiliar with them and their needs to survive. I just picked up two small 12V lamps that I am familiar with.

Deezler · 05-20-2009, 07:25 PM

Oh yeah, they need a voltage regulator. Doh. Incandescent bulbs it is then.

Seems like basically every car would have standard coolant fan relays and thus an 87 terminal to grab a bulb source from. I'm doing this asap! Good luck with yours.

fit7ad · 05-20-2009, 08:58 PM

Quote:

Originally Posted by Deezler

Oh yeah, they need a voltage regulator. Doh. Incandescent bulbs it is then.

Seems like basically every car would have standard coolant fan relays and thus an 87 terminal to grab a bulb source from. I'm doing this asap! Good luck with yours.

The regulator is just a simple resistor to limit the current flow to the LED. Most "regular" LEDs (not super brights or things with clear lenses) requires only 5 mA to 10 mA. Typical resistor value of 1.5 Kohm to 3 Kohm gets you 5 to 10 mA when connected to 13.5 V. You can play with the resistor value to see how bright you want it. Just test it on any +12V source with the engine running. Being careful not to short out anything goes without saying. Having a switch to select 2 different brightness would not be a bad idea.

When using an LED, you don't really need a fuse. I usually tap into the circuit using one end of the resistor and run a wire from the other end of the resistor to where I need. If the wire ever gets shorted, the resistor will restrict the current to a safe small number. For those who don't know, an LED has a + and - terminal.