What is this plug for? - The 1947 - Present Chevrolet & GMC Truck Message Board Network

Hazieview · 12-21-2011, 09:04 AM

This is a factory engine harness for my 81 Chevy. What is this plug for?

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terryj · 12-21-2011, 11:36 AM

Were you running a Q-jet on the engine, this could be TRV harness. If you've changed carburators it may no longer be needed. The TRV (Throttle Return Valve) is used on the Q-jets to prevent fuel loading (rich mixture) when decelerating.

Hazieview · 12-21-2011, 10:53 PM

Thank you very much kind sir!
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Telecasterjoey · 12-21-2011, 11:33 PM

looks to me like the plug that goes onto the little canister that threds onto a y pipe that threads into the block on the rear of the motor just behind the seam where the intake meets the block. Crappy explanation i know. I just did an engine swap and I'm certain thats where that plug goes. In this pic its dead center behind the carb holes just past the intake its the little silverish can behind the intake close to the firewall. It plugs into that lol

Hope this helps, If you need more info let me know i'll get a better pic!

raws67 · 12-22-2011, 03:51 AM

Looks like its for the oil pressure switch. The light blue wire should go to an electric choke. I had an 84 with one like that and it went to a switch just above the oil filter. I believe some trucks also hooked up by the sending unit behind the intake. Basically it goes to a switch that senses oil pressure so your electric choke will work or the choke light will come on. Not 100% positive its been awhile.

Hazieview · 12-22-2011, 01:00 PM

Ok so what I am understanding is that the plug should hook to the oil sending unit behind the block.

When the plug senses oil pressure from the sending unit it feeds a switch.

This switch activates an electric choke on the carb.

I'm running a sb400 and I can not locate any oil pressure swithch. I also have an Edelbrock carb now.

Can this plug be eliminated?

Hazieview · 12-22-2011, 01:42 PM

This plug feeds the oil pressure switch tapped off the Y. The other Y side of the 'Y' feeds the oil sender. Thanks guys! One wire eliminated!

motornut · 12-23-2011, 02:13 AM

check pics in post 199 in my 78 jimmy below
not have one here?
or just above the oil filter a 1/4 inch drive hole

motornut · 12-23-2011, 07:38 AM

You may have to buy the switch,can you find the hole?
They come factory equipped don't have to drill it.
But they do break off flush...
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Better ask Santa for a camera

12-21-2011, 09:04 AM	#1
Hazieview Building Dreams out of Dimes! Join Date: May 2005 Location: Bonham, Tx Posts: 892	What is this plug for? This is a factory engine harness for my 81 Chevy. What is this plug for? [IMG][/IMG] Posted via Mobile Device __________________ 1981 Chevy short/wide. SB400 350th

12-21-2011, 11:36 AM	#2
terryj Registered User Join Date: Aug 2010 Location: Medford, Oregon Posts: 139	Re: What is this plug for? Were you running a Q-jet on the engine, this could be TRV harness. If you've changed carburators it may no longer be needed. The TRV (Throttle Return Valve) is used on the Q-jets to prevent fuel loading (rich mixture) when decelerating.

12-21-2011, 10:53 PM	#3
Hazieview Building Dreams out of Dimes! Join Date: May 2005 Location: Bonham, Tx Posts: 892	Re: What is this plug for? Thank you very much kind sir! Posted via Mobile Device __________________ 1981 Chevy short/wide. SB400 350th

12-21-2011, 11:33 PM	#4
Telecasterjoey Registered User Join Date: Nov 2010 Location: Ottawa ON Posts: 514	Re: What is this plug for? looks to me like the plug that goes onto the little canister that threds onto a y pipe that threads into the block on the rear of the motor just behind the seam where the intake meets the block. Crappy explanation i know. I just did an engine swap and I'm certain thats where that plug goes. In this pic its dead center behind the carb holes just past the intake its the little silverish can behind the intake close to the firewall. It plugs into that lol Hope this helps, If you need more info let me know i'll get a better pic! Attached Images

12-22-2011, 03:51 AM	#5
raws67 Registered User Join Date: Jun 2007 Location: lemoore ca Posts: 126	Re: What is this plug for? Looks like its for the oil pressure switch. The light blue wire should go to an electric choke. I had an 84 with one like that and it went to a switch just above the oil filter. I believe some trucks also hooked up by the sending unit behind the intake. Basically it goes to a switch that senses oil pressure so your electric choke will work or the choke light will come on. Not 100% positive its been awhile.

12-22-2011, 01:00 PM	#6
Hazieview Building Dreams out of Dimes! Join Date: May 2005 Location: Bonham, Tx Posts: 892	Re: What is this plug for? Ok so what I am understanding is that the plug should hook to the oil sending unit behind the block. When the plug senses oil pressure from the sending unit it feeds a switch. This switch activates an electric choke on the carb. I'm running a sb400 and I can not locate any oil pressure swithch. I also have an Edelbrock carb now. Can this plug be eliminated? __________________ 1981 Chevy short/wide. SB400 350th

12-22-2011, 01:42 PM	#7
Hazieview Building Dreams out of Dimes! Join Date: May 2005 Location: Bonham, Tx Posts: 892	Re: What is this plug for? This plug feeds the oil pressure switch tapped off the Y. The other Y side of the 'Y' feeds the oil sender. Thanks guys! One wire eliminated! __________________ 1981 Chevy short/wide. SB400 350th

12-23-2011, 02:13 AM	#8
motornut 78K & 79C Jimmys Join Date: Nov 2009 Location: Ottawa Ont CANADA Posts: 7,901	Re: What is this plug for? check pics in post 199 in my 78 jimmy below not have one here? or just above the oil filter a 1/4 inch drive hole __________________ John 1978 GMCJimmy4X4-350/203 1979 GMCJimmy4X2-305/350

12-23-2011, 07:38 AM	#9
motornut 78K & 79C Jimmys Join Date: Nov 2009 Location: Ottawa Ont CANADA Posts: 7,901	Re: What is this plug for? You may have to buy the switch,can you find the hole? They come factory equipped don't have to drill it. But they do break off flush... Posted via Mobile Device Better ask Santa for a camera __________________ John 1978 GMCJimmy4X4-350/203 1979 GMCJimmy4X2-305/350



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