Help - wiring question - The 1947 - Present Chevrolet & GMC Truck Message Board Network

**ScottH** · 03-20-2004, 08:19 PM

I noticed today that when I was trying to trace the wiring in my 72, there appears to be a piece missing. It is a small silver box located above the fuse box on the inside. Normally I believe there are two, but the top one in my truck is missing.

If anyone can tell me what this is normally used for I would appreciate it. I have a parts truck with one on it still, but want to be sure it is needed before I start rewiring my driver inorder to replace it.

Any info is really appreciated.

Thanks!

cdowns · 03-20-2004, 08:41 PM

above the fusebox to the right is a square silver relay that is for the horn should have red/black/dark green wires going to it

Sweet72 · 03-20-2004, 08:44 PM

Possibly the TCS (transmission controlled spark/temperature controlled spark) relay, or maybe the horn relay. Some folks just delete the TCS system altogether since its purpose is to limit ign. timing advance to occur only when coolant temp is above 82* and the trans is in high gear.

cdowns · 03-20-2004, 09:05 PM

the horn relay is inside the cab by the fusebox

Sweet72 · 03-20-2004, 09:37 PM

On the 1972 Chev/GMC model C10-30 trucks the TCS relay is mounted inside the cab above the horn relay.

**ScottH** · 03-20-2004, 10:42 PM

Thanks guys. In regards to the TCS, would it be present in a truck originally equipped with a 3 speed manual? My 72 driver is an auto, but the parts truck was a manual. If so any differences? And can anyone tell me what wires went to the TCS and where they went too?

Thanks again!!!

Sweet72 · 03-21-2004, 02:04 AM

Yep, the manuals, had TCS too. Component locations will be different in a I6 as compared to a small V8. The trans switch is different between man. and auto transmissions, being mechanically actuated in the manual and pressure actuated in the auto. The system uses the same components otherwise. If you're really interested in restoring this system, you should obtain a copy of the 1972 10-30 series truck service manual. It explains system operation, components and has complete wiring diagrams. Good luck on your resto.
-Sam

**ScottH** · 03-21-2004, 11:27 AM

Thanks to everyone for the great info and help!

03-20-2004, 08:19 PM	#1
ScottH Senior Member Join Date: Sep 2002 Location: Hampstead, NC Posts: 8,187	Help - wiring question I noticed today that when I was trying to trace the wiring in my 72, there appears to be a piece missing. It is a small silver box located above the fuse box on the inside. Normally I believe there are two, but the top one in my truck is missing. If anyone can tell me what this is normally used for I would appreciate it. I have a parts truck with one on it still, but want to be sure it is needed before I start rewiring my driver inorder to replace it. Any info is really appreciated. Thanks!

03-20-2004, 08:41 PM	#2
cdowns Senior Member Join Date: Jan 2003 Location: daytonabeach Posts: 22,956	above the fusebox to the right is a square silver relay that is for the horn should have red/black/dark green wires going to it __________________ 71c-10 350/2004r/4:11 lowered3/4 longbed/dead by hurricane MEANING OF DEATH::::: SOMEBODY ELSE GETS YOUR STUFF DONT BELIEVE EVERYTHING YOU THINK TAKE MY ADVISE;I DON'T USE IT ANYWAY

03-20-2004, 08:44 PM	#3
Sweet72 Registered User Join Date: Nov 2003 Location: Alexandria, VA Posts: 1,534	Possibly the TCS (transmission controlled spark/temperature controlled spark) relay, or maybe the horn relay. Some folks just delete the TCS system altogether since its purpose is to limit ign. timing advance to occur only when coolant temp is above 82* and the trans is in high gear. __________________ '72 GMC SWB C1500 Custom, frame-off in progress. 383 SBC, 9:1CR, Comp Cams XE262H, Scat internal balanced crank, Eagle SIR 6" rods, Keith Black dish pistons, Dart Iron Eagle 72/180 heads, Weiand Stealth intake, Stewart stage I water pump, Holley 4bbl vac sec, TH350 with B&M Shift Improver Kit. 12 bolt positraction. Last edited by Sweet72; 03-20-2004 at 10:19 PM.

03-20-2004, 09:05 PM	#4
cdowns Senior Member Join Date: Jan 2003 Location: daytonabeach Posts: 22,956	the horn relay is inside the cab by the fusebox __________________ 71c-10 350/2004r/4:11 lowered3/4 longbed/dead by hurricane MEANING OF DEATH::::: SOMEBODY ELSE GETS YOUR STUFF DONT BELIEVE EVERYTHING YOU THINK TAKE MY ADVISE;I DON'T USE IT ANYWAY

03-20-2004, 09:37 PM	#5
Sweet72 Registered User Join Date: Nov 2003 Location: Alexandria, VA Posts: 1,534	On the 1972 Chev/GMC model C10-30 trucks the TCS relay is mounted inside the cab above the horn relay. __________________ '72 GMC SWB C1500 Custom, frame-off in progress. 383 SBC, 9:1CR, Comp Cams XE262H, Scat internal balanced crank, Eagle SIR 6" rods, Keith Black dish pistons, Dart Iron Eagle 72/180 heads, Weiand Stealth intake, Stewart stage I water pump, Holley 4bbl vac sec, TH350 with B&M Shift Improver Kit. 12 bolt positraction. Last edited by Sweet72; 03-20-2004 at 09:44 PM.

03-20-2004, 10:42 PM	#6
ScottH Senior Member Join Date: Sep 2002 Location: Hampstead, NC Posts: 8,187	Thanks guys. In regards to the TCS, would it be present in a truck originally equipped with a 3 speed manual? My 72 driver is an auto, but the parts truck was a manual. If so any differences? And can anyone tell me what wires went to the TCS and where they went too? Thanks again!!!

03-21-2004, 02:04 AM	#7
Sweet72 Registered User Join Date: Nov 2003 Location: Alexandria, VA Posts: 1,534	Yep, the manuals, had TCS too. Component locations will be different in a I6 as compared to a small V8. The trans switch is different between man. and auto transmissions, being mechanically actuated in the manual and pressure actuated in the auto. The system uses the same components otherwise. If you're really interested in restoring this system, you should obtain a copy of the 1972 10-30 series truck service manual. It explains system operation, components and has complete wiring diagrams. Good luck on your resto. -Sam __________________ '72 GMC SWB C1500 Custom, frame-off in progress. 383 SBC, 9:1CR, Comp Cams XE262H, Scat internal balanced crank, Eagle SIR 6" rods, Keith Black dish pistons, Dart Iron Eagle 72/180 heads, Weiand Stealth intake, Stewart stage I water pump, Holley 4bbl vac sec, TH350 with B&M Shift Improver Kit. 12 bolt positraction.

03-21-2004, 11:27 AM	#8
ScottH Senior Member Join Date: Sep 2002 Location: Hampstead, NC Posts: 8,187	Thanks to everyone for the great info and help!



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