Whats This Electrical Contraption? - The 1947 - Present Chevrolet & GMC Truck Message Board Network

Blue85 · 03-25-2009, 01:33 AM

So, I was wiring in my tach today, hooking up to the dist. cap, I notice that is already a yellow wire coming from the tach, leading to what I think is a relay of some kind mounted on the valve cover. Ive never dealt with one these before, my 74 never had it, nor did my 85, can someone please explain what this is, and how it works?

Blue85 · 03-25-2009, 01:34 AM

Cant get pics to upload, the relay is mounted on the driver side valve cover, the truck has a 350 motor/th400 tranny

flamingbig10 · 03-25-2009, 02:05 AM

does it go to any thing

Blue85 · 03-25-2009, 11:50 AM

here is the pic>>>

Longhorn321 · 03-25-2009, 12:19 PM

I have no idea but I am interested to know. It might help if you told the year, make and model of truck this is on.
As an aside, why are the V/Cs blue? You're not on here asking about a F@%d are you?

jchav62 · 03-25-2009, 12:48 PM

I wonder if it's something for the "ESC-Electronic spark control" that these trucks used to come out with? Does the dist. have a vacuum advance?

Blue85 · 03-25-2009, 02:13 PM

The truck is a 1980 GMC K10, 350 motor, I was kinda wondering too why the valve covers were painted like that. But yesterday i was also wondering why the P.O. had the stereo power wire jammed into the horn fuse

Prerunner1982 · 03-25-2009, 02:22 PM

I was thinking perhaps it is a kill switch? Especially if it is wired to the distributor. The relay would open and close the power to the coil.

Blue85 · 03-25-2009, 02:32 PM

So i took the harness off and this is what i found, still have no clue of its original purpose.

westie 666 · 03-25-2009, 03:06 PM

Quote:

Originally Posted by Longhorn321

why are the V/Cs blue? You're not on here asking about a F@%d are you?

Some trucks came out with blue motors, my 77 has a blue motor so I kept it like that, the only thing was I could only get old F@#D blue to repaint it.

73chevyman · 03-25-2009, 03:30 PM

well does it still run with out it. if so forget about it lol. hook the tach up and move on. but it probably something to do with a alarm or a kill switch of some sort

Blue85 · 03-25-2009, 03:47 PM

Oh yeah, she still runs without it, its amazing how much wiring and emissions things you can remove from these trucks and they still run just as good, sometimes better.

JohnC · 03-25-2009, 05:05 PM

Yeah I know. Mine has the majority of the vacuum lines capped off. Still runs fine so on we go!

enaberif · 03-25-2009, 05:16 PM

Quote:

Originally Posted by JohnC

Yeah I know. Mine has the majority of the vacuum lines capped off. Still runs fine so on we go!

I only have 2 vacuum lines: Transmission and Distributor

jchav62 · 03-25-2009, 05:55 PM

Quote:

Originally Posted by enaberif

I only have 2 vacuum lines: Transmission and Distributor

I have four...those two, the brake booster and the PCV...

88 Dippy · 03-25-2009, 06:53 PM

i only have the dizzy vacuum and break booster

red caddy · 03-25-2009, 11:15 PM

I have that same setup on my '86 1 ton, No clue what it does or what connects to the 3 rd plug. I looked in an '86 Motors manual, went cross eyed reading the schematic's before I found any thing that resembled that harness.

Did the mid 80's trucks have a clutch interlock (like some Ford trucks) that would only let the engine crank if the clutch pedal was down?

This one has me scratchin' my little bald head... RED

DirtyLarry · 03-26-2009, 01:09 AM

That is weird. I have never seen an OEM relay bolted to the valve cover, of all places, on any GM vehicle. It just doesn't look like something the General would do. A relay right on a heat source doesn't seem like a good idea. I am guess this is somekind of relay contraption for some aftermarket dodad. Maybe some long gone JC Whitney cruise control contraption or something.

Blue engines came to be around 1977 or 78. Then they became black after 1981.

Blue85 · 03-26-2009, 01:18 AM

looks pretty factory, gm logos on plugs and relay, mounting bracket on valve cover has factory style spot welds etc. Cruise was my first thought too, but the truck has factory cruise that works.

ElGracho · 03-26-2009, 07:22 AM

Is there a key lock cylinder in the fender?

Rob73-87 · 03-26-2009, 04:35 PM

That has been done by the previous owner !

I have the same relay in my cabin under the dash - and THAT`S ORIGINAL.
My truck has been a diesel, so I think it has something to do with the pre-glowing of the diesel engine !!?
I`m not quite sure about that - if someone knows better please correct me.

Rob

lurch115 · 03-26-2009, 09:05 PM

Quote:

Originally Posted by Rob73-87

That has been done by the previous owner !

I have the same relay in my cabin under the dash - and THAT`S ORIGINAL.
My truck has been a diesel, so I think it has something to do with the pre-glowing of the diesel engine !!?
I`m not quite sure about that - if someone knows better please correct me.

Rob

if the truck was converted from a diesel to a gas that relay and such would have stayed with the diesel since the diesels don't use a distributor, and they also have different valve covers.... that and the glow plug controller is larger than that relay...

sierra4x4 · 03-26-2009, 09:20 PM

I know that is factory becouse I have two truck with the exact same thing. One is a 84 3/4 ton 2wd with a 350/TH400 all original powertrain. The other is a 86 3/4 ton 4wd with a 350/TH400 and it also has it. Ihave no clue what it does though.

Blue85 · 03-27-2009, 12:25 AM

Somewhere i'm sure somebody knows what this is lol. Where in sask are you from sierra4x4?

f.monroe · 03-27-2009, 12:41 AM

I do not really deal with the 81 and up trucks but from the sound of things , its may be a kickdown relay for the th400 . I know that they are electrick kickdown and all of the trucks mentioned above that have one also have th400's . I have never seen one like that or if I have , I didnt pay attention to it .
Frank

03-25-2009, 01:33 AM	#1
Blue85 Oilfield Trash Join Date: Sep 2003 Location: Raymore, Sk, Canada, Earth Posts: 3,170	Whats This Electrical Contraption? So, I was wiring in my tach today, hooking up to the dist. cap, I notice that is already a yellow wire coming from the tach, leading to what I think is a relay of some kind mounted on the valve cover. Ive never dealt with one these before, my 74 never had it, nor did my 85, can someone please explain what this is, and how it works? __________________ 14 Dodge 3500 Mega Cab 08 Dodge 3500 Mega Cab 87 Chev 3+3 4x4 80 GMC K10 High Sierra bone stock 70 Chevelle 350SS long term project 68 GMC 3ton Grain Truck/Garbage wagon 50 Pontiac 2 Door Coupe Project "I've got a shotgun rifle and a 4 wheel drive and a country boy can survive" Hank Jr.

03-25-2009, 01:34 AM	#2
Blue85 Oilfield Trash Join Date: Sep 2003 Location: Raymore, Sk, Canada, Earth Posts: 3,170	Re: Whats This Electrical Contraption? Cant get pics to upload, the relay is mounted on the driver side valve cover, the truck has a 350 motor/th400 tranny __________________ 14 Dodge 3500 Mega Cab 08 Dodge 3500 Mega Cab 87 Chev 3+3 4x4 80 GMC K10 High Sierra bone stock 70 Chevelle 350SS long term project 68 GMC 3ton Grain Truck/Garbage wagon 50 Pontiac 2 Door Coupe Project "I've got a shotgun rifle and a 4 wheel drive and a country boy can survive" Hank Jr.

03-25-2009, 02:05 AM	#3
flamingbig10 6.0 powered square Join Date: Feb 2008 Location: Mesquite texas Posts: 3,459	Re: Whats This Electrical Contraption? does it go to any thing __________________ Aaron 1980 c-10 short bed lowered, cammed 6.0, 4l80e 3600 stall, smp tune, wilwoods, and flames best time so far best et 7.86 @87 on motor 7.57 90 on a 75 shot Build http://67-72chevytrucks.com/vboard/s...d.php?t=283326

03-25-2009, 11:50 AM	#4
Blue85 Oilfield Trash Join Date: Sep 2003 Location: Raymore, Sk, Canada, Earth Posts: 3,170	Re: Whats This Electrical Contraption? here is the pic>>> Attached Images __________________ 14 Dodge 3500 Mega Cab 08 Dodge 3500 Mega Cab 87 Chev 3+3 4x4 80 GMC K10 High Sierra bone stock 70 Chevelle 350SS long term project 68 GMC 3ton Grain Truck/Garbage wagon 50 Pontiac 2 Door Coupe Project "I've got a shotgun rifle and a 4 wheel drive and a country boy can survive" Hank Jr.

03-25-2009, 12:19 PM	#5
Longhorn321 Size Matters Join Date: Aug 2007 Location: Lyman, SC Posts: 9,189	Re: Whats This Electrical Contraption? I have no idea but I am interested to know. It might help if you told the year, make and model of truck this is on. As an aside, why are the V/Cs blue? You're not on here asking about a F@%d are you? __________________ "Reading the owners manual is only for quitters." Jason Harper, Bloomberg News. ...WOOOO HOOOO!!!!

03-25-2009, 12:48 PM	#6
jchav62 1962 C-10 Join Date: Apr 2005 Location: Las Vegas, New Mexico Posts: 4,978	Re: Whats This Electrical Contraption? I wonder if it's something for the "ESC-Electronic spark control" that these trucks used to come out with? Does the dist. have a vacuum advance? __________________ Joseph Chavez "See the USA in a Chevrolet!!" ......................_____ .........________//__{\_____ ,,,,,,,/__(O)___//___/__(O)_/ 1962 C10 Shortbed Fleetside 327/th350 GV overdrive 1974 C10 Longbed Fleetside 350/th350 "The Trash Truck" 1999 Chevy 2500 OBS, Longbed 5.7/4L80E 4x4 2015 GMC Sierra SLE 1500 4x4

03-25-2009, 02:13 PM	#7
Blue85 Oilfield Trash Join Date: Sep 2003 Location: Raymore, Sk, Canada, Earth Posts: 3,170	Re: Whats This Electrical Contraption? The truck is a 1980 GMC K10, 350 motor, I was kinda wondering too why the valve covers were painted like that. But yesterday i was also wondering why the P.O. had the stereo power wire jammed into the horn fuse __________________ 14 Dodge 3500 Mega Cab 08 Dodge 3500 Mega Cab 87 Chev 3+3 4x4 80 GMC K10 High Sierra bone stock 70 Chevelle 350SS long term project 68 GMC 3ton Grain Truck/Garbage wagon 50 Pontiac 2 Door Coupe Project "I've got a shotgun rifle and a 4 wheel drive and a country boy can survive" Hank Jr.

03-25-2009, 02:22 PM	#8
Prerunner1982 Registered User Join Date: Oct 2002 Location: Edmond, OK Posts: 5,904	Re: Whats This Electrical Contraption? I was thinking perhaps it is a kill switch? Especially if it is wired to the distributor. The relay would open and close the power to the coil. __________________ Jon 1982 Chevy Silverado 350/th350.... RETIRED 1993 Jeep XJ 2 door(Cherokee) 4wd 4.0ltr/AX-15 (5spd)/NP231 .... Oklahoma Roll Call

03-25-2009, 02:32 PM	#9
Blue85 Oilfield Trash Join Date: Sep 2003 Location: Raymore, Sk, Canada, Earth Posts: 3,170	Re: Whats This Electrical Contraption? So i took the harness off and this is what i found, still have no clue of its original purpose. Attached Images __________________ 14 Dodge 3500 Mega Cab 08 Dodge 3500 Mega Cab 87 Chev 3+3 4x4 80 GMC K10 High Sierra bone stock 70 Chevelle 350SS long term project 68 GMC 3ton Grain Truck/Garbage wagon 50 Pontiac 2 Door Coupe Project "I've got a shotgun rifle and a 4 wheel drive and a country boy can survive" Hank Jr.

03-25-2009, 03:30 PM	#11
73chevyman Registered User Join Date: Nov 2008 Location: Lusby, MD Posts: 563	Re: Whats This Electrical Contraption? well does it still run with out it. if so forget about it lol. hook the tach up and move on. but it probably something to do with a alarm or a kill switch of some sort __________________ http://67-72chevytrucks.com/vboard/group.php?groupid=37 73 C10 Fleetside If it ain't a Chevy it's foreign http://hotridesmag.com/

03-25-2009, 03:47 PM	#12
Blue85 Oilfield Trash Join Date: Sep 2003 Location: Raymore, Sk, Canada, Earth Posts: 3,170	Re: Whats This Electrical Contraption? Oh yeah, she still runs without it, its amazing how much wiring and emissions things you can remove from these trucks and they still run just as good, sometimes better. __________________ 14 Dodge 3500 Mega Cab 08 Dodge 3500 Mega Cab 87 Chev 3+3 4x4 80 GMC K10 High Sierra bone stock 70 Chevelle 350SS long term project 68 GMC 3ton Grain Truck/Garbage wagon 50 Pontiac 2 Door Coupe Project "I've got a shotgun rifle and a 4 wheel drive and a country boy can survive" Hank Jr.

03-25-2009, 05:05 PM	#13
JohnC Registered User Join Date: Feb 2009 Location: Oklahoma Posts: 7,461	Re: Whats This Electrical Contraption? Yeah I know. Mine has the majority of the vacuum lines capped off. Still runs fine so on we go!

03-25-2009, 06:53 PM	#16
88 Dippy Registered User Join Date: Feb 2009 Location: mt. Pleasant, MI Posts: 246	Re: Whats This Electrical Contraption? i only have the dizzy vacuum and break booster __________________ 1974 chevy Cheyenne C10 "The Mutt":4x4 convertion, NP208, 700-R4, stock 350, edelbrock Torker intake, edelbrock 600 CFM carb, duels 2001 Pontiac Grand Prix GT: 3.8L supercharged, 9.2:1 comprestion, ZZP XP cam, home made intake, 2 1/2" exhuast, 10psi of boost

03-25-2009, 11:15 PM	#17
red caddy Registered User Join Date: Dec 2008 Location: Venice Florida Posts: 83	Re: Whats This Electrical Contraption? I have that same setup on my '86 1 ton, No clue what it does or what connects to the 3 rd plug. I looked in an '86 Motors manual, went cross eyed reading the schematic's before I found any thing that resembled that harness. Did the mid 80's trucks have a clutch interlock (like some Ford trucks) that would only let the engine crank if the clutch pedal was down? This one has me scratchin' my little bald head... RED

03-26-2009, 01:09 AM	#18
DirtyLarry Windy Corner of a Dirty Street Join Date: Jun 2003 Location: Pueblo West, Colorado Posts: 2,926	Re: Whats This Electrical Contraption? That is weird. I have never seen an OEM relay bolted to the valve cover, of all places, on any GM vehicle. It just doesn't look like something the General would do. A relay right on a heat source doesn't seem like a good idea. I am guess this is somekind of relay contraption for some aftermarket dodad. Maybe some long gone JC Whitney cruise control contraption or something. Blue engines came to be around 1977 or 78. Then they became black after 1981. __________________ Current vehicle collection: 1978 Chevrolet K10, 8.1L, NV4500, NP205 1989 Chevrolet Suburban, 8.1L, NV4500, NP241 1993 Chevrolet C1500 Sportside, TBI 7.4L, 4L60E 2001 Chevrolet K2500HD, Ext Cab, SWB, 8.1L, ZF 6 speed 2014 Chevrolet Impala LTZ 3.6L Vortec 8.1L because life is too short to tolerate underpowered vehicles Instagram



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03-26-2009, 01:18 AM	#19
Blue85 Oilfield Trash Join Date: Sep 2003 Location: Raymore, Sk, Canada, Earth Posts: 3,170	Re: Whats This Electrical Contraption? looks pretty factory, gm logos on plugs and relay, mounting bracket on valve cover has factory style spot welds etc. Cruise was my first thought too, but the truck has factory cruise that works. __________________ 14 Dodge 3500 Mega Cab 08 Dodge 3500 Mega Cab 87 Chev 3+3 4x4 80 GMC K10 High Sierra bone stock 70 Chevelle 350SS long term project 68 GMC 3ton Grain Truck/Garbage wagon 50 Pontiac 2 Door Coupe Project "I've got a shotgun rifle and a 4 wheel drive and a country boy can survive" Hank Jr. Last edited by Blue85; 03-26-2009 at 01:23 AM.

03-26-2009, 07:22 AM	#20
ElGracho Gentleman Jim Driver Join Date: Nov 2002 Location: Poulsbo, WA Posts: 1,553	Re: Whats This Electrical Contraption? Is there a key lock cylinder in the fender? __________________ Joe '75 GMC Gentleman Jim '84 Chev C10 Short Wide - Super duper plain (manual steering, manual brakes, no dome light, no cig lighter) '85 Chev C10 Short Wide - Super plain Vortec 4.8 4L60E trans also: '81 K30, '83 C30 Crew Dually, '84 M1028 CUCV, '85 M1009 CUCV, another '85 C10 SWB, '89 R3500 Flatbed

03-26-2009, 04:35 PM	#21
Rob73-87 Registered User Join Date: Feb 2008 Location: Nuremberg, Germany Posts: 116	Re: Whats This Electrical Contraption? That has been done by the previous owner ! I have the same relay in my cabin under the dash - and THAT`S ORIGINAL. My truck has been a diesel, so I think it has something to do with the pre-glowing of the diesel engine !!? I`m not quite sure about that - if someone knows better please correct me. Rob

03-26-2009, 09:20 PM	#23
sierra4x4 Registered User Join Date: Jan 2009 Location: Canada Posts: 308	Re: Whats This Electrical Contraption? I know that is factory becouse I have two truck with the exact same thing. One is a 84 3/4 ton 2wd with a 350/TH400 all original powertrain. The other is a 86 3/4 ton 4wd with a 350/TH400 and it also has it. Ihave no clue what it does though.

03-27-2009, 12:25 AM	#24
Blue85 Oilfield Trash Join Date: Sep 2003 Location: Raymore, Sk, Canada, Earth Posts: 3,170	Re: Whats This Electrical Contraption? Somewhere i'm sure somebody knows what this is lol. Where in sask are you from sierra4x4? __________________ 14 Dodge 3500 Mega Cab 08 Dodge 3500 Mega Cab 87 Chev 3+3 4x4 80 GMC K10 High Sierra bone stock 70 Chevelle 350SS long term project 68 GMC 3ton Grain Truck/Garbage wagon 50 Pontiac 2 Door Coupe Project "I've got a shotgun rifle and a 4 wheel drive and a country boy can survive" Hank Jr.

03-27-2009, 12:41 AM	#25
f.monroe Senior Member Join Date: May 2004 Location: Caldwell,Tx. Posts: 3,648	Re: Whats This Electrical Contraption? I do not really deal with the 81 and up trucks but from the sound of things , its may be a kickdown relay for the th400 . I know that they are electrick kickdown and all of the trucks mentioned above that have one also have th400's . I have never seen one like that or if I have , I didnt pay attention to it . Frank __________________ Born and proudly residing in a Red State !

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