What are these solonoid looking things on my firewall for?? - The 1947 - Present Chevrolet & GMC Truck Message Board Network

Yamariv · 02-26-2023, 01:43 PM

Hey guys,

I was redoing my HEI distributor power wire this week and noticed a second bundle of wires running to my engine that were not connected to anything. The HEI power wire bundle ran together with all the starter wires but this second bundle came from these solonoid looking parts on my fire wall and went to my engine for some reason.

I looked on the wiring diagrams but didn't have much luck, what are these wires for? Truck seems to run perfect without any of them hooked up..

**truckster** · 02-26-2023, 02:44 PM

TCS - transmission controlled spark. It was an early emissions device. You can safely delete it.

Yamariv · 02-26-2023, 04:05 PM

Quote:

Originally Posted by truckster

TCS - transmission controlled spark. It was an early emissions device. You can safely delete it.

Oh wow interesting!! So I can delete both of those little boxes?

Out of curiosity, how did that emissions system work?

Yamariv · 02-26-2023, 04:13 PM

FYI, found this on another forum..

The TCS system was there ONLY for EPA emissions purpose. It did NOTHING for the engine, for economy, or for performance.

Basically, it retarded timing when the transmission (either manual or auto) was in lower ranges, but dropped out if the engine was either too hot or too cold and/or if WOT was employed. A retarded engine will run hotter in the combustion chamber and burn off more of the residual hydrocarbons.

**truckster** · 02-26-2023, 06:45 PM

Quote:

Originally Posted by Yamariv

Oh wow interesting!! So I can delete both of those little boxes?

Out of curiosity, how did that emissions system work?

I've only seen TCS systems with a single relay. Can you move the black wire loom so it's easier to see what's going on there?

Yamariv · 02-26-2023, 07:55 PM

Quote:

Originally Posted by truckster

I've only seen TCS systems with a single relay. Can you move the black wire loom so it's easier to see what's going on there?

Took some more pics from different angles for you, hope it helps!

**Steeveedee** · 02-26-2023, 08:47 PM

The TCS relay has dark blue and dark green wires to it. The other item is not part of the TCS system.

Yamariv · 02-27-2023, 01:09 PM

Quote:

Originally Posted by Steeveedee

The TCS relay has dark blue and dark green wires to it. The other item is not part of the TCS system.

Dang, any idea where I could find out what the other relay is for? Wiring diagrams maybe? I'd really like to get rid of that whole second harness..they arent connected to anything right now

**Steeveedee** · 02-27-2023, 02:06 PM

OK, Looking at this wiring diagram, that says (O2 only), if I'm reading it right. That's an 18 ga tan wire on it. Up near the top right it shows heater blower power (Except O2). I'm drawing a blank, maybe someone with more electrical knowledge can point you right. Does your heater blower work?

Yamariv · 02-27-2023, 08:12 PM

Quote:

Originally Posted by Steeveedee

OK, Looking at this wiring diagram, that says (O2 only), if I'm reading it right. That's an 18 ga tan wire on it. Up near the top right it shows heater blower power (Except O2). I'm drawing a blank, maybe someone with more electrical knowledge can point you right. Does your heater blower work?

Gah, I'm not too good at reading those electrical diagrams either. Yes, the blower motor works but only on a low setting, maybe it's medium I can't tell. Where do you see that tan wire going to a blower? Fixing the blower motor switch is on my list. Lol

**Steeveedee** · 02-27-2023, 08:42 PM

OK, I don't know what "O2" means. But it does seem to indicate some difference in the heater blower motor wiring. Many times when I get into the nitty-gritty details with things like this on the internet, it seems like I get it wrong, so I want someone with more experience to weigh in. If I had the truck in front of me, I'd be able to figure it out.

Yamariv · 02-27-2023, 10:12 PM

Quote:

Originally Posted by Steeveedee

OK, I don't know what "O2" means. But it does seem to indicate some difference in the heater blower motor wiring. Many times when I get into the nitty-gritty details with things like this on the internet, it seems like I get it wrong, so I want someone with more experience to weigh in. If I had the truck in front of me, I'd be able to figure it out.

Sounds good, hope someone chimes in! :S

Yamariv · 03-02-2023, 08:22 PM

Just a quick thread update.. I posted in the electrical section but didn't get any further info on the second solenoid so I decided to remove the whole harness and solenoid setup and see if the truck still runs. Yup, ran fine, both these solenoids can hit the junk pile incase someone is wondering about their truck. These are just for the TCS emissions system.

Engine bay looks much cleaner now and I only have one harness running to the engine. Woohoo

02-26-2023, 01:43 PM	#1
Yamariv Registered User Join Date: Oct 2022 Location: Regina, Saskatchewan Posts: 343	What are these solonoid looking things on my firewall for?? Hey guys, I was redoing my HEI distributor power wire this week and noticed a second bundle of wires running to my engine that were not connected to anything. The HEI power wire bundle ran together with all the starter wires but this second bundle came from these solonoid looking parts on my fire wall and went to my engine for some reason. I looked on the wiring diagrams but didn't have much luck, what are these wires for? Truck seems to run perfect without any of them hooked up.. Attached Images __________________ 1971 Chev C10 - 250ci L6 w/3 speed on the floor Upgrades: Power Steering 3 Core Radiator 7 Hole Gauge Cluster Power Brakes (Incoming!!..) 1971 350 (Incoming!!..)

02-26-2023, 02:44 PM	#2
truckster Senior Member Join Date: Jan 2001 Location: Orem, Utah Posts: 7,886	Re: What are these solonoid looking things on my firewall for?? TCS - transmission controlled spark. It was an early emissions device. You can safely delete it. __________________ I have sworn upon the altar of God, eternal hostility against every form of tyranny over the mind of man. - Thomas Jefferson

02-26-2023, 04:13 PM	#4
Yamariv Registered User Join Date: Oct 2022 Location: Regina, Saskatchewan Posts: 343	Re: What are these solonoid looking things on my firewall for?? FYI, found this on another forum.. The TCS system was there ONLY for EPA emissions purpose. It did NOTHING for the engine, for economy, or for performance. Basically, it retarded timing when the transmission (either manual or auto) was in lower ranges, but dropped out if the engine was either too hot or too cold and/or if WOT was employed. A retarded engine will run hotter in the combustion chamber and burn off more of the residual hydrocarbons. __________________ 1971 Chev C10 - 250ci L6 w/3 speed on the floor Upgrades: Power Steering 3 Core Radiator 7 Hole Gauge Cluster Power Brakes (Incoming!!..) 1971 350 (Incoming!!..)

02-26-2023, 08:47 PM	#7
Steeveedee Who Changed This? Join Date: Jan 2013 Location: Simi Valley, CA Posts: 10,338	Re: What are these solonoid looking things on my firewall for?? The TCS relay has dark blue and dark green wires to it. The other item is not part of the TCS system. __________________ ~Steven '70 Chevy 3/4T Longhorn CST 402/400/3.56 Custom Camper Simi Valley, CA

02-27-2023, 02:06 PM	#9
Steeveedee Who Changed This? Join Date: Jan 2013 Location: Simi Valley, CA Posts: 10,338	Re: What are these solonoid looking things on my firewall for?? OK, Looking at this wiring diagram, that says (O2 only), if I'm reading it right. That's an 18 ga tan wire on it. Up near the top right it shows heater blower power (Except O2). I'm drawing a blank, maybe someone with more electrical knowledge can point you right. Does your heater blower work? Attached Images __________________ ~Steven '70 Chevy 3/4T Longhorn CST 402/400/3.56 Custom Camper Simi Valley, CA

02-27-2023, 08:42 PM	#11
Steeveedee Who Changed This? Join Date: Jan 2013 Location: Simi Valley, CA Posts: 10,338	Re: What are these solonoid looking things on my firewall for?? OK, I don't know what "O2" means. But it does seem to indicate some difference in the heater blower motor wiring. Many times when I get into the nitty-gritty details with things like this on the internet, it seems like I get it wrong, so I want someone with more experience to weigh in. If I had the truck in front of me, I'd be able to figure it out. __________________ ~Steven '70 Chevy 3/4T Longhorn CST 402/400/3.56 Custom Camper Simi Valley, CA

03-02-2023, 08:22 PM	#13
Yamariv Registered User Join Date: Oct 2022 Location: Regina, Saskatchewan Posts: 343	Re: What are these solonoid looking things on my firewall for?? Just a quick thread update.. I posted in the electrical section but didn't get any further info on the second solenoid so I decided to remove the whole harness and solenoid setup and see if the truck still runs. Yup, ran fine, both these solenoids can hit the junk pile incase someone is wondering about their truck. These are just for the TCS emissions system. Engine bay looks much cleaner now and I only have one harness running to the engine. Woohoo __________________ 1971 Chev C10 - 250ci L6 w/3 speed on the floor Upgrades: Power Steering 3 Core Radiator 7 Hole Gauge Cluster Power Brakes (Incoming!!..) 1971 350 (Incoming!!..)



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