Idiot Lights - LED and Standard Bulbs, Working Together

Every car has an electrical system. Here's the place to learn all about it.

Moderator: 2088 bob

Post Reply
User avatar
CBDZ
Posts: 168
Joined: Mon Jun 01, 2009 11:22 am
Location: Just up-wind of all the Chino Dairies
Contact:

Idiot Lights - LED and Standard Bulbs, Working Together

Post by CBDZ » Wed Apr 20, 2016 5:41 pm

I’m looking for a little help on how to wire a second “idiot” light for both the Oil Pressure, and Alternator Charge lights. I have a stock speedometer, with the stock Oil & Alt bulbs installed. I also have installed in the dash two Large LED lights which would be more visible than the two speedometer mounted gauges.

Prior to mounting the two LED lights, both the oil and alt worked perfectly.

Now that I have mounted the two LED lights, I have two issues.

1. This is the more important of the two, but I don’t have a functioning charge system.
2. The oil pressure LED will light, but the standard speedometer incandescent bulb will not.

This is how I have them wired. What do I need to change in order to get proper function?

Image
Last edited by CBDZ on Wed Apr 20, 2016 10:27 pm, edited 1 time in total.
My Car Details:
Fiberglass Buggy on 1973 Chassis.
1904 cc
Megasquirt (MS1 with 3.57 board) Fuel Injection: German Intake Plenum, CB Performance End-Castings, Ford Escort Throttle Body with custom Adapter, MS controls Wasted Spark Coil Pack

User avatar
Marc
Moderator
Posts: 23721
Joined: Thu May 23, 2002 2:01 am
Contact:

Re: Idiot Lights - LED and Standard Bulbs, Working Together

Post by Marc » Wed Apr 20, 2016 9:28 pm

Diagram's not showing.

User avatar
CBDZ
Posts: 168
Joined: Mon Jun 01, 2009 11:22 am
Location: Just up-wind of all the Chino Dairies
Contact:

Re: Idiot Lights - LED and Standard Bulbs, Working Together

Post by CBDZ » Wed Apr 20, 2016 10:27 pm

-----------------Fixed Photo Link-------------
Last edited by CBDZ on Wed Apr 20, 2016 11:00 pm, edited 1 time in total.
My Car Details:
Fiberglass Buggy on 1973 Chassis.
1904 cc
Megasquirt (MS1 with 3.57 board) Fuel Injection: German Intake Plenum, CB Performance End-Castings, Ford Escort Throttle Body with custom Adapter, MS controls Wasted Spark Coil Pack

User avatar
Marc
Moderator
Posts: 23721
Joined: Thu May 23, 2002 2:01 am
Contact:

Re: Idiot Lights - LED and Standard Bulbs, Working Together

Post by Marc » Wed Apr 20, 2016 10:37 pm

Yes, and as I suspected you've wired them in series rather than parallel. Try this:
Image

Note that sometimes enough voltage manages to backfeed from the alternator, through the LED, to the ignition switch (and thence to the coil) that the engine won't shut off when you turn off the key :shock: ....depends upon the characteristics of the LED and the coil. If you have this problem, get back to us - you'll have to go to Radio Shack (or open up some junk old transistor radio/whatever) to get a diode to wire in between the LED and the alternator...meanwhile, disconnect the - lead from the LED.

Unlike incandescent bulbs, LEDs are polarity sensitive - so if an LED doesn't work, reverse the leads going to it. If it's one that has its polarity marked, you want the + lead going to the ignition switch.
Last edited by Marc on Wed Apr 20, 2016 11:36 pm, edited 2 times in total.

User avatar
CBDZ
Posts: 168
Joined: Mon Jun 01, 2009 11:22 am
Location: Just up-wind of all the Chino Dairies
Contact:

Re: Idiot Lights - LED and Standard Bulbs, Working Together

Post by CBDZ » Wed Apr 20, 2016 11:29 pm

Thanks a ton. After you said that it needed to be parallel, I know exactly what I needed to do.

Will I need a resister at the LED for the Alt.? Will the current flow along the path of least resistance, and therefore bypass the Speedo light, causing a "not charging" condition?

I already have the diode at the Alternator.
My Car Details:
Fiberglass Buggy on 1973 Chassis.
1904 cc
Megasquirt (MS1 with 3.57 board) Fuel Injection: German Intake Plenum, CB Performance End-Castings, Ford Escort Throttle Body with custom Adapter, MS controls Wasted Spark Coil Pack

User avatar
Marc
Moderator
Posts: 23721
Joined: Thu May 23, 2002 2:01 am
Contact:

Re: Idiot Lights - LED and Standard Bulbs, Working Together

Post by Marc » Wed Apr 20, 2016 11:41 pm

Current will ALWAYS follow the path of least resistance, but in a parallel circuit there'll still be some current going through the high-resistance side (since the same voltage differential exists on both paths)...if the incandescent bulb doesn't light, I suppose you might have to add resistance in series with the LED but I don't think it should be needed in this application, pretty sure that's only a concern to make the flasher work when using LEDs as turn signals. I've never tried your setup before, please be sure to tell us how it works out for you.

The resistance of the stock warning lamp should be in the 100Ω ballpark. (R=V^2/W) ....so if it's necessary to add a resistor to balance the branch load, subtract the forward resistance of the LED from that to get a value to try. http://www.instructables.com/id/Determi ... s-of-LEDs/

User avatar
CBDZ
Posts: 168
Joined: Mon Jun 01, 2009 11:22 am
Location: Just up-wind of all the Chino Dairies
Contact:

Re: Idiot Lights - LED and Standard Bulbs, Working Together

Post by CBDZ » Thu Apr 21, 2016 12:51 am

I rewired in parallel WITHOUT the resister. The lights in the speedometer DO NOT light, and I am not getting a charging Alternator. Looks like I need to go hunt down some resisters. :-(

It looks like I need to do something like this, but what is the diode doing? Is that the "after-run" diode?
Image
My Car Details:
Fiberglass Buggy on 1973 Chassis.
1904 cc
Megasquirt (MS1 with 3.57 board) Fuel Injection: German Intake Plenum, CB Performance End-Castings, Ford Escort Throttle Body with custom Adapter, MS controls Wasted Spark Coil Pack

User avatar
Dale M.
Posts: 1602
Joined: Mon Oct 05, 2009 10:09 am
Location: Just a Little Bit West Of Yosemite Valley

Re: Idiot Lights - LED and Standard Bulbs, Working Together

Post by Dale M. » Thu Apr 21, 2016 8:54 am

Diode is "anti run on"... You are pretty close with "after run"....

Image

Dale
Lives his life vicariously through his own self.
1970 "Kellison Sand Piper Roadster"

Post Reply