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10-20-2021, 11:32 AM | #1 |
Carpe manana
Join Date: Dec 2010
Location: Eau Claire, WI
Posts: 12,410
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Why might this relay be in use?
I’m slowly unwinding all the electrical changes made to my 99 Suburban that was formerly operated by a municipal fire department.
This relay appears spliced into an engine harness bundle at one end and the passenger side battery at the other end (red wire with an in-line fuse). The truck dies if this wire is removed at the battery. At the harness end it looks like a red harness wire was cut and spliced to the blue and yellow wires from the relay. Not sure why this modification was done other than a possible anti-theft option. Any other thoughts? I don’t have the schematic for this truck like I do my 72s and want the wiring back to original.
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1972 K5 CST Highlander Blazer: http://67-72chevytrucks.com/vboard/s...d.php?t=708547 1972 K20 Cheyenne Super: http://67-72chevytrucks.com/vboard/s...d.php?t=528308 Members met: ORANGBLAZ, 2003 silverado, MikeCofield, BB72CHEVKT, Duncan&Son, Sameyrasmea72, THENEWMEXICAN, HotRod C/10, brianthelion02, Sport/Truck, ryanroo, michael bustamante, Dirt's72, Already Gone, WestButteTruck, 57taskforce, Moreyel, painterljp, AASmedic, SoCoC10, Lumaestas, carbuff382, Chevyland |
10-21-2021, 05:22 AM | #2 |
Senior Member
Join Date: Dec 1999
Location: Southern California
Posts: 2,828
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Re: Why might this relay be in use?
I would look at the coil side of the relay and see where they go to determine what relay is for. One side should go to ground and the other to +12v. Either side could be switched depending on application. One side may go to 12v and other switched to ground or one side to ground and other switched to 12v.
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Richard 1972 K10 Custom Deluxe SWB Fleetside My build https://67-72chevytrucks.com/vboard/...d.php?t=800746 |
10-21-2021, 11:20 AM | #3 |
Senior Member
Join Date: Mar 2003
Location: Colfax-California
Posts: 8,571
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Re: Why might this relay be in use?
Where does the yellow wire go??
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10-21-2021, 10:18 PM | #4 |
Carpe manana
Join Date: Dec 2010
Location: Eau Claire, WI
Posts: 12,410
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Re: Why might this relay be in use?
Thanks guys. The yellow and blue wires out of the relay each join separated ends of a red wire at the harness. The green wire out the relay is a ground and the red out the relay is wired right to the pos battery terminal. I’m combing through some GM literature trying to nail down what the red harness wire supplies.
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1972 K5 CST Highlander Blazer: http://67-72chevytrucks.com/vboard/s...d.php?t=708547 1972 K20 Cheyenne Super: http://67-72chevytrucks.com/vboard/s...d.php?t=528308 Members met: ORANGBLAZ, 2003 silverado, MikeCofield, BB72CHEVKT, Duncan&Son, Sameyrasmea72, THENEWMEXICAN, HotRod C/10, brianthelion02, Sport/Truck, ryanroo, michael bustamante, Dirt's72, Already Gone, WestButteTruck, 57taskforce, Moreyel, painterljp, AASmedic, SoCoC10, Lumaestas, carbuff382, Chevyland |
10-26-2021, 07:38 AM | #5 |
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Join Date: Aug 2011
Location: China Spring, TX
Posts: 7,280
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Re: Why might this relay be in use?
What does that red wire at the harness feed or do?
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Master Chief, US Navy, Retired 1964 C10 Step-side Short Bed - In Progress 2009 2500HD Duramax LTZ 1948 GMC Panel 1956 Big Window Stepside 1953 5 Window Chevy Stepside 1932 Coupe New Seat Foam for Bench Seats? |
10-27-2021, 12:50 AM | #6 |
Senior Member
Join Date: Mar 2003
Location: Colfax-California
Posts: 8,571
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Re: Why might this relay be in use?
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10-27-2021, 06:28 AM | #7 | |
Moderator
Join Date: Aug 2011
Location: China Spring, TX
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Re: Why might this relay be in use?
Quote:
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Master Chief, US Navy, Retired 1964 C10 Step-side Short Bed - In Progress 2009 2500HD Duramax LTZ 1948 GMC Panel 1956 Big Window Stepside 1953 5 Window Chevy Stepside 1932 Coupe New Seat Foam for Bench Seats? Last edited by The Rocknrod; 10-27-2021 at 06:38 AM. |
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10-27-2021, 09:36 AM | #8 |
Carpe manana
Join Date: Dec 2010
Location: Eau Claire, WI
Posts: 12,410
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Re: Why might this relay be in use?
Unsure - I need to track that down still and I imagine that's key to solving the puzzle. If I d/c the hot from the battery to the relay the engine dies. I'm clueless with diesel engines to be honest.
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1972 K5 CST Highlander Blazer: http://67-72chevytrucks.com/vboard/s...d.php?t=708547 1972 K20 Cheyenne Super: http://67-72chevytrucks.com/vboard/s...d.php?t=528308 Members met: ORANGBLAZ, 2003 silverado, MikeCofield, BB72CHEVKT, Duncan&Son, Sameyrasmea72, THENEWMEXICAN, HotRod C/10, brianthelion02, Sport/Truck, ryanroo, michael bustamante, Dirt's72, Already Gone, WestButteTruck, 57taskforce, Moreyel, painterljp, AASmedic, SoCoC10, Lumaestas, carbuff382, Chevyland |
10-27-2021, 04:25 PM | #9 |
Registered User
Join Date: Oct 2005
Location: Overland Park, Ks.
Posts: 5,224
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Re: Why might this relay be in use?
It may be a glow plug relay. Possibly a fuel shutoff relay. Electric fan maybe. It is not factory installed.
George |
10-28-2021, 09:16 AM | #10 | |
Carpe manana
Join Date: Dec 2010
Location: Eau Claire, WI
Posts: 12,410
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Re: Why might this relay be in use?
Quote:
I'll d/c the added wire it when I get the chance and restore continuity to the OE harness wire and see what happens.
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1972 K5 CST Highlander Blazer: http://67-72chevytrucks.com/vboard/s...d.php?t=708547 1972 K20 Cheyenne Super: http://67-72chevytrucks.com/vboard/s...d.php?t=528308 Members met: ORANGBLAZ, 2003 silverado, MikeCofield, BB72CHEVKT, Duncan&Son, Sameyrasmea72, THENEWMEXICAN, HotRod C/10, brianthelion02, Sport/Truck, ryanroo, michael bustamante, Dirt's72, Already Gone, WestButteTruck, 57taskforce, Moreyel, painterljp, AASmedic, SoCoC10, Lumaestas, carbuff382, Chevyland |
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10-29-2021, 03:07 PM | #11 |
Registered User
Join Date: Oct 2005
Location: Overland Park, Ks.
Posts: 5,224
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Re: Why might this relay be in use?
If the engine dies when you d-c the wire then it most likely is for the fuel shut off.
George |
10-29-2021, 09:21 PM | #12 |
Senior Member
Join Date: Mar 2003
Location: Colfax-California
Posts: 8,571
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Re: Why might this relay be in use?
I'm looking at a picture where the yellow and blue wire both turn to pink at the overheated solder/shrink connector
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