Electrical gremlin found and fixed
Thread Starter
Racer
Joined: Oct 2008
Posts: 249
Likes: 0
From: Heath Texas
Electrical gremlin found and fixed
I had a thread concerning a short that cause fused #2 to pop (footwell). This is the circuit for the underhood light, fader mirror control, map lights, and vanity mirror.
I finally gave up the basic diagnostic routine (pull bulbs, plugging in fuses, repeatedly blowing fuses). I am a total dufus on spark chasing.
Took the Z by a local Vette mechanic. Turned out to be a stuck relay in the circuit. Was charged only one hour labor (he spent 3 on it) and the price of the part.
I'm assuming that one crude diagnostic would be to bridge the fuse contacts, a stuck relay would heat up to the point of going supernova. Is there another less combustible way of checking relays?
I finally gave up the basic diagnostic routine (pull bulbs, plugging in fuses, repeatedly blowing fuses). I am a total dufus on spark chasing.
Took the Z by a local Vette mechanic. Turned out to be a stuck relay in the circuit. Was charged only one hour labor (he spent 3 on it) and the price of the part.
I'm assuming that one crude diagnostic would be to bridge the fuse contacts, a stuck relay would heat up to the point of going supernova. Is there another less combustible way of checking relays?
Tech Contributor
Joined: Jan 2007
Posts: 19,421
Likes: 1,146
From: Dyer, IN
I had a thread concerning a short that cause fused #2 to pop (footwell). This is the circuit for the underhood light, fader mirror control, map lights, and vanity mirror.
I finally gave up the basic diagnostic routine (pull bulbs, plugging in fuses, repeatedly blowing fuses). I am a total dufus on spark chasing.
Took the Z by a local Vette mechanic. Turned out to be a stuck relay in the circuit. Was charged only one hour labor (he spent 3 on it) and the price of the part.
I'm assuming that one crude diagnostic would be to bridge the fuse contacts, a stuck relay would heat up to the point of going supernova. Is there another less combustible way of checking relays?
I finally gave up the basic diagnostic routine (pull bulbs, plugging in fuses, repeatedly blowing fuses). I am a total dufus on spark chasing.
Took the Z by a local Vette mechanic. Turned out to be a stuck relay in the circuit. Was charged only one hour labor (he spent 3 on it) and the price of the part.
I'm assuming that one crude diagnostic would be to bridge the fuse contacts, a stuck relay would heat up to the point of going supernova. Is there another less combustible way of checking relays?
Thread Starter
Racer
Joined: Oct 2008
Posts: 249
Likes: 0
From: Heath Texas
Safety Car
Joined: May 2008
Posts: 4,237
Likes: 11
From: Lacombe Louisiana
I dont see how a "stuck" relay would cause this problem if there isnt another problem downstream from it.I merely supplies voltage,if it left components "on" it would simply run down the battery. Maybe it had an internal short to ground?
Tech Contributor
Joined: Dec 1999
Posts: 32,910
Likes: 2,402
From: Anthony TX
CI 6,7,8,9,11 Vet
St. Jude Donor '08
A relay has TWO basic working parts:
The OPEN & CLOSED contacts that change states when the relay operates.
The COIL that gets 12 VDC battery voltage when the relay is energized that pulls the relay arm to move the movable contacts.
The COIL has a engineered resistance that allows it to be connected to the battery "circuit" and properly operate without overheating or dropping out. That resistance is measured in OHMs. Its usually 1-10 ohms (depending on how frequently or how long it is energized) but,,,if the internal COIL degrades and shorts (wire wraps break down and cause a Short circuit with in the coil making LESS coil resistance), the resistance changes to LESS than the engineered resistance and the fuse that protects the circuit sees more current than its designed to see and it BLOWS.
If you look in the GM Service manual and troubleshoot a DTC, or problem, the bubble chart will provide you the relay coil resistance that is expected.
BC
The OPEN & CLOSED contacts that change states when the relay operates.
The COIL that gets 12 VDC battery voltage when the relay is energized that pulls the relay arm to move the movable contacts.
The COIL has a engineered resistance that allows it to be connected to the battery "circuit" and properly operate without overheating or dropping out. That resistance is measured in OHMs. Its usually 1-10 ohms (depending on how frequently or how long it is energized) but,,,if the internal COIL degrades and shorts (wire wraps break down and cause a Short circuit with in the coil making LESS coil resistance), the resistance changes to LESS than the engineered resistance and the fuse that protects the circuit sees more current than its designed to see and it BLOWS.
If you look in the GM Service manual and troubleshoot a DTC, or problem, the bubble chart will provide you the relay coil resistance that is expected.
BC
Tech Contributor
Joined: Dec 2006
Posts: 10,962
Likes: 29
From: Van Buren Arkansas
Wounded Warrior Escort '11
Valid point if the coil shorts out...then it certainly could blow the fuse. The relay would then result in being stuck so maybe this is what they found.
Advanced
Joined: Jun 2009
Posts: 64
Likes: 0
From: Portage Indiana
A stuck relay WILL blow a fuse on the circuit that is in the coil circuit. The reason is because of the pull in current required to mechanically move the relays moveable tips. If the moveable part doesn't fully move to the closed position, the flux lines caused by the current in the coil remain unsaturated (a little electro-magnetic theory) and the coil heats up causing even higher current. Suffice it to say, a stuck relay will in fact blow a fuse, with no grounds or shorts!!
Corvette Stories
The Best of Corvette for Corvette Enthusiasts
How Much Horsepower Every Corvette Engine "LOST" in 1972
Joe Kucinski
Top 10 DOs and DON'Ts for Protecting Your Convertible Top!
Michael S. Palmer
Top 10 Most Explosive Corvettes Ever Made: Power-to-Weight Ratio Ranked!
Joe Kucinski
150 hp to 1,250 hp: Every Corvette Generation Compared by the Specs That Matter
Joe Kucinski
8 Coolest Corvette Pace Cars (and Replicas) of All Time
Verdad Gallardo
Top 10 Corvette Engines RANKED by Peak Torque (70+ Years of Muscle!)
Joe Kucinski
Corvette ZR1X Will Be Pacing the Indy 500, And Could Probably Race, Too!
Verdad Gallardo
Top 10 Corvettes Coming to Mecum Indy 2026!
Brett Foote
Top 10 C9 Corvette MUST-HAVES to Fix These C8 Generation Flaws!
Michael S. Palmer
Melting Slicks
Joined: Oct 2007
Posts: 2,383
Likes: 13
From: Kinston North Carolina
This Thread contains some correct info, and some incorrect info. Before I say anymore, I want someone to look at the schematic and tell me which relay could stick and blow Fuse #2.
Advanced
Joined: Jun 2009
Posts: 64
Likes: 0
From: Portage Indiana
[QUOTE=byronhunter;1571667771]This Thread contains some correct info, and some incorrect info. Before I say anymore, I want someone to look at the schematic and tell me which relay could stick and blow Fuse #2.QUOTE]
If you're refering to my responce, you may want to rethink your comment. My post didn't say anything about #2 fuse or any particular relay. It was worded as an explaination of how a mechanically stuck relay can blow a fuse without any shorts or grounds. In my business, (power plant electrical maintenance) we see it all the time.
If you're refering to my responce, you may want to rethink your comment. My post didn't say anything about #2 fuse or any particular relay. It was worded as an explaination of how a mechanically stuck relay can blow a fuse without any shorts or grounds. In my business, (power plant electrical maintenance) we see it all the time.
Thread Starter
Racer
Joined: Oct 2008
Posts: 249
Likes: 0
From: Heath Texas
I don't remember which relay the guy replaced (I'll ask the next time). All I know is that that circuit is working perfectly now. I've gone out of my way to test it, because the shop guy said he wasn't 100% sure that was it or there was something else down the line.
I'll crank on the fader, vanity lights, both map lights and open the hood for extended time just to put on a load and test. Does just fine. Bad relay, looks like.
I'll crank on the fader, vanity lights, both map lights and open the hood for extended time just to put on a load and test. Does just fine. Bad relay, looks like.
