Underhood Wire Harness Question - The 1947 - Present Chevrolet & GMC Truck Message Board Network

Travis K · 01-01-2008, 02:15 PM

Got a question about underhood wiring here. I had to do some rewiring under my hood due to a previous hack job, and switching to an internal regulated alternator. Can anyone explain this harness to me? It is not in any wiring diagrams that I have seen so far. The green wire goes to a 2nd temp sensor (not the one that goes to the main engine harness), The black wire goes to the transmission (TH350), and the brown, brown/yellow, and blue wire go to a connector that looks like an alternator connector, but is not the alternator connector. The brown wire on that connector also has a small connector that links to the brown wire on the main harness that goes to the alternator. I am not sure where the large connector goes. These wires on my 71 are all terminated. Can someone explain this harness to me, and what these relays are for?

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Travis K · 01-01-2008, 02:16 PM

I forgot to mention that the relays mount to the firewall just above the park brake cable.

**Palf70Step** · 01-01-2008, 02:18 PM

If I remember right the green wire was for some solenoid/relay for the carb....an early model pollution thing.
Edit:

I just remmebered I had this, maybe it will help.

**john** · 01-01-2008, 02:28 PM

Those are for TCS (transmission controlled spark) which operated a vacuum solenoid for the vacuum advance. Vacuum advance only when engine is at operating temp and transmission in high gear.The temp sensor was in the pass side head and the vacuum solenoid mounted on the intake manifold, the high gear switch in the trans.

Travis K · 01-01-2008, 02:38 PM

Palf70step, thanks for the diagram. I have been using that one already, and I can't find this relay setup on it.

Where does the connector that looks like the alternator connector go to? I do not have a vacuum solenoid on my intake manifold as far as I know. Can this setup be thrown out? My engine is running fine, my only problem is that the truck won't move. You can read about that one in my other post.

01-01-2008, 02:15 PM	#1
Travis K Registered User Join Date: Mar 2007 Location: Bismarck, ND Posts: 81	Underhood Wire Harness Question Got a question about underhood wiring here. I had to do some rewiring under my hood due to a previous hack job, and switching to an internal regulated alternator. Can anyone explain this harness to me? It is not in any wiring diagrams that I have seen so far. The green wire goes to a 2nd temp sensor (not the one that goes to the main engine harness), The black wire goes to the transmission (TH350), and the brown, brown/yellow, and blue wire go to a connector that looks like an alternator connector, but is not the alternator connector. The brown wire on that connector also has a small connector that links to the brown wire on the main harness that goes to the alternator. I am not sure where the large connector goes. These wires on my 71 are all terminated. Can someone explain this harness to me, and what these relays are for?

01-01-2008, 02:16 PM	#2
Travis K Registered User Join Date: Mar 2007 Location: Bismarck, ND Posts: 81	Re: Underhood Wire Harness Question I forgot to mention that the relays mount to the firewall just above the park brake cable.

01-01-2008, 02:18 PM	#3
Palf70Step State of Confusion! Join Date: Jul 2002 Location: Gulfport, MS USA Posts: 47,083	Re: Underhood Wire Harness Question If I remember right the green wire was for some solenoid/relay for the carb....an early model pollution thing. Edit: I just remmebered I had this, maybe it will help. __________________ Bill 1970 Chevy Custom/10 LWB Fleetside 2010 Toyota Tacoma PreRunner SR5 Double Cab - DD Member of Louisiana Classic Truck Club (LCTC) Bill's Gallery Life isn't tied with a bow, but it's still a gift. Live simply. Love generously. Care deeply. Speak kindly. Leave the rest to God! Last edited by Palf70Step; 01-01-2008 at 02:34 PM.

01-01-2008, 02:28 PM	#4
john member #16 Join Date: Dec 1999 Location: Yuba City Ca. Posts: 3,618	Re: Underhood Wire Harness Question Those are for TCS (transmission controlled spark) which operated a vacuum solenoid for the vacuum advance. Vacuum advance only when engine is at operating temp and transmission in high gear.The temp sensor was in the pass side head and the vacuum solenoid mounted on the intake manifold, the high gear switch in the trans. __________________ john http://67-72chevytrucks.com/vboard/showgroups.php board vendors http://www.flickr.com/photos/1745471...7602865984234/ Last edited by john; 01-01-2008 at 02:32 PM.

01-01-2008, 02:38 PM	#5
Travis K Registered User Join Date: Mar 2007 Location: Bismarck, ND Posts: 81	Re: Underhood Wire Harness Question Palf70step, thanks for the diagram. I have been using that one already, and I can't find this relay setup on it. Where does the connector that looks like the alternator connector go to? I do not have a vacuum solenoid on my intake manifold as far as I know. Can this setup be thrown out? My engine is running fine, my only problem is that the truck won't move. You can read about that one in my other post.



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