 Powering a light with two different sources of 12 Volt power, one doesn't affect the other |
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| Tom |
 Sep 22 2012, 01:48 PM
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#1
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Advanced Member  Group: Members Posts: 2,139 Joined: 21-August 05 From: Port Orchard, WA 98367 Member No.: 4,626 Region Association: None  |
Possible by using two steering diodes. I believe 1N4001 diodes will support 1 amp. Should be more than enough for a small indicator lamp.
Jim, one power from relay ( black/yellow), other from fan. Tom Attached thumbnail(s) 
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| jim_hoyland |
Sep 22 2012, 03:47 PM
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#2
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Get that VIN ? Group: Members Posts: 9,696 Joined: 1-May 03 From: Sunset Beach, CA Member No.: 643 Region Association: Southern California 
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I am attempting to use some of the CAT wiring to turn on the CAT light ( it's a 75 ) when the oil cooler fan comes on.
CAT light always comes on at start up, then goes out when engine is started. The CAT sensor is not Kinstalled. My thought is to use the wiring that goes from the rear trunk to the dash to indicate the fan is on. Here's a wiring diagram of the harness in the rear trunk. There is a relay involved. I'm also thinking it will be easier to run a wire from the fan through the tunnel and jump into the CAT light connector too. ** I previously referred to this as the EGR circuit, but was mistaken. This is the circuit found in the rear trunk with a pair of wires going to the sensor Attached thumbnail(s) 
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| tradisrad |
Sep 22 2012, 05:08 PM
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#3
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Senior Member Group: Members Posts: 985 Joined: 11-September 06 From: San Mateo, CA Member No.: 6,815 Region Association: Northern California |
If the EGR indicator is nonfunctional disconnect its wire from the dash and attach your fan wire.
I installed an LED into my oil temp gauge to indicate when my fan is on.  |
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| Cap'n Krusty |
Sep 22 2012, 05:09 PM
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#4
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Cap'n Krusty Group: Members Posts: 10,794 Joined: 24-June 04 From: Santa Maria, CA Member No.: 2,246 Region Association: Central California |
Had me baffled for a moment, then I decided you meant "EGR", not "ERG". Since you no longer have an EGR, why not just wire the light directly to the source you'll be monitoring?
The Cap'n |
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| jim_hoyland |
Sep 22 2012, 05:52 PM
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#5
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Get that VIN ? Group: Members Posts: 9,696 Joined: 1-May 03 From: Sunset Beach, CA Member No.: 643 Region Association: Southern California
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QUOTE(tradisrad @ Sep 22 2012, 04:08 PM)  If the EGR indicator is nonfunctional disconnect its wire from the dash and attach your fan wire. I installed an LED into my oil temp gauge to indicate when my fan is on. I like that better. What's involved in drilling the hole... |
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| tradisrad |
Sep 22 2012, 09:06 PM
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#6
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Senior Member Group: Members Posts: 985 Joined: 11-September 06 From: San Mateo, CA Member No.: 6,815 Region Association: Northern California |
I bought the LED at Frys Electronics. I was sure to get an LED with a bezel. I took the gauge apart and drilled the hole by hand (it came out a little lower than I wanted). The needle clears the LED. I used a variable resistor on the LED to control the brightness .
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| Mike Bellis |
Sep 22 2012, 09:11 PM
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#7
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Resident Electrician Group: Members Posts: 8,347 Joined: 22-June 09 From: Midlothian TX Member No.: 10,496 Region Association: None 
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QUOTE(Tom @ Sep 22 2012, 12:48 PM) Possible by using two steering diodes. I believe 1N4001 diodes will support 1 amp. Should be more than enough for a small indicator lamp. Jim, one power from relay ( black/yellow), other from fan. Tom Are you making 1 idiot light illuminate from 2 sources? It's a little unclear, your intentions. If so I agree with your simple schematic. (IMG:style_emoticons/default/smile.gif) I did this same thing with my custom EFI system. Various signals can turn on the "check engine" light. |
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| Tom |
Sep 23 2012, 02:02 AM
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#8
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Advanced Member Group: Members Posts: 2,139 Joined: 21-August 05 From: Port Orchard, WA 98367 Member No.: 4,626 Region Association: None |
Mike,
Yes, two different power sources to light one lamp. It is for Jim in post 2. Tom |
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