need info on relay - The 1947 - Present Chevrolet & GMC Truck Message Board Network

*edin355* · 08-18-2008, 08:01 PM

I recently purchased a 72 swb Ac truck.Im in the process of redoing some of the wiring.Ac cabs are new to me.Next to the horn relay under the dash in another relay with a red,blue,black,andb/w wires. They run into the engine compartment about two foot long and then they were cut off.I have searched books with wiring diagrams but cant find anything showint this relay.Im almost sure it has to do with the ac.I would think maybe it was cut from the wiring hub where the main wires are joined,but dont know for sure. Any help would be greatly appreciated. Thanks for any help. edin 355

*edin355* · 08-19-2008, 01:11 PM

Could someone with AC please give me some in sight on this problem.

Hutch · 08-19-2008, 02:29 PM

edin355
Here is a link to a wiring diagram:
http://67-72chevytrucks.com/vboard/s...d.php?t=185665

From your description I do not think that the relay you are describing has anything to do with the A/C.

463 · 08-19-2008, 02:42 PM

Justin has the wiring dia here. http://67-72chevytrucks.com/vboard/s...=185856&page=5 the wire you list red,blue, black and b/w tells me that it was hooked to a after market realy like a bosh unit to run a higher curent device.

neonlarry · 08-19-2008, 04:25 PM

Is the relay simular in appearance to the horn relay? If so my best guess is that it is the TCS (transmission controlled spark) relay.

463 · 08-19-2008, 07:02 PM

Quote:

Originally Posted by neonlarry

Is the relay simular in appearance to the horn relay? If so my best guess is that it is the TCS (transmission controlled spark) relay.

this 72 truck would not have had a tcs,

JimKshortstep4x4 · 08-19-2008, 08:09 PM

As mentioned it is probably an after market relay setup as the other relay it could have been is the anti-dieseling relay which was located close to the heater controls. The wires to the anti-dieseling relay were pink, dark green and orange. The relay for the AC unit should be mounted on the heater box by the passenger's side.

Jim

*edin355* · 08-20-2008, 01:07 PM

Thanks for the info. This has to be a stock relay.I saw one on a 72 blazer located in the same place.It goes out to the engine bay through a plug above the fuse box. The one on the blazer has been cut off at about two foot also.So because of the plug and the way the wiring was wrapped I know it must be a stock item on ac units.Someone on this board with ac must have one like this.I greatly appreciate all of the feed back so far.Still looking for someone with ac that has this relay on their truck. Thanks for any and all help.

*edin355* · 08-20-2008, 01:14 PM

Bigblock you said something about being used with ac compressor.If so do you know where it is wired to?I would like to make up any wiring harness that I might need.

Big Block · 08-19-2008, 08:04 PM

The relay is for your a/c compressor. If you are going to try to use the original a/c unit you will need to get the under hood a/c harness

08-18-2008, 08:01 PM	#1
edin355 Account Suspended Join Date: Apr 2005 Location: jEFFERSON cITY mO. Posts: 130	need info on relay I recently purchased a 72 swb Ac truck.Im in the process of redoing some of the wiring.Ac cabs are new to me.Next to the horn relay under the dash in another relay with a red,blue,black,andb/w wires. They run into the engine compartment about two foot long and then they were cut off.I have searched books with wiring diagrams but cant find anything showint this relay.Im almost sure it has to do with the ac.I would think maybe it was cut from the wiring hub where the main wires are joined,but dont know for sure. Any help would be greatly appreciated. Thanks for any help. edin 355

08-19-2008, 01:11 PM	#2
edin355 Account Suspended Join Date: Apr 2005 Location: jEFFERSON cITY mO. Posts: 130	Re: need info on relay Could someone with AC please give me some in sight on this problem.

08-19-2008, 02:29 PM	#3
Hutch Registered User Join Date: Oct 2001 Location: Grapevine, Tx. Posts: 2,142	Re: need info on relay edin355 Here is a link to a wiring diagram: http://67-72chevytrucks.com/vboard/s...d.php?t=185665 From your description I do not think that the relay you are describing has anything to do with the A/C. __________________ John Hutchison Grapevine,Texas 68 1/2 t swb 68 Mustang 69 Jaguar 71 1/2 t swb 88 Supra CompTs6m 93 Escort GT 2005 Corolla XRS

08-19-2008, 02:42 PM	#4
463 Registered User Join Date: Nov 2007 Location: Sask Canada Posts: 1,666	Re: need info on relay Justin has the wiring dia here. http://67-72chevytrucks.com/vboard/s...=185856&page=5 the wire you list red,blue, black and b/w tells me that it was hooked to a after market realy like a bosh unit to run a higher curent device. __________________ Trueman

08-19-2008, 04:25 PM	#5
neonlarry Registered User Join Date: Feb 2002 Location: Vacaville, CA Posts: 2,746	Re: need info on relay Is the relay simular in appearance to the horn relay? If so my best guess is that it is the TCS (transmission controlled spark) relay. __________________ 70 C/10 Light Red 350/TH350, HEI, Duals w/40 series Flows, 91 seat, LED taillights 99 Pontiac S/C GTP, SLP Ram Air hood, GMPP Konis & springs 95 Neon ACR, MP PCM, AFX UDP, 3.0 CAI

08-19-2008, 08:09 PM	#7
JimKshortstep4x4 Senior Member Join Date: Jul 2001 Location: Muskegon,MI,USA Posts: 6,026	Re: need info on relay As mentioned it is probably an after market relay setup as the other relay it could have been is the anti-dieseling relay which was located close to the heater controls. The wires to the anti-dieseling relay were pink, dark green and orange. The relay for the AC unit should be mounted on the heater box by the passenger's side. Jim __________________ 1971 Shortbox step side 4x4, 350 sbc, 3:07 rear end 1965 Impala SS 400 sbc, Muncie rock crusher 1966 Impala SS 396 bbc, TH 400 1969 El Camino, 350 sbc, TH 350 1971 Snowplow built on a Blazer frame 1972 GMC Short bed, stepside, TH 400, 427 BBC Last edited by JimKshortstep4x4; 08-19-2008 at 08:11 PM. Reason: Spelling

08-20-2008, 01:07 PM	#8
edin355 Account Suspended Join Date: Apr 2005 Location: jEFFERSON cITY mO. Posts: 130	Re: need info on relay Thanks for the info. This has to be a stock relay.I saw one on a 72 blazer located in the same place.It goes out to the engine bay through a plug above the fuse box. The one on the blazer has been cut off at about two foot also.So because of the plug and the way the wiring was wrapped I know it must be a stock item on ac units.Someone on this board with ac must have one like this.I greatly appreciate all of the feed back so far.Still looking for someone with ac that has this relay on their truck. Thanks for any and all help.

08-20-2008, 01:14 PM	#9
edin355 Account Suspended Join Date: Apr 2005 Location: jEFFERSON cITY mO. Posts: 130	Re: need info on relay Bigblock you said something about being used with ac compressor.If so do you know where it is wired to?I would like to make up any wiring harness that I might need.

08-19-2008, 08:04 PM	#10
Big Block Big Block Join Date: Mar 2005 Location: Durham, N.C. Posts: 1,649	Re: need info on relay The relay is for your a/c compressor. If you are going to try to use the original a/c unit you will need to get the under hood a/c harness

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