I am putting a complete wiring harness from a 72 El Camino 350 auto ac into a 72 El Camino 350 4 speed ac, two questions
What is a LT V8 DELAY RELAY? What does it do? and do I need it on a man trans car? It was in the harness from the parts car.
Same questions about the TCS RELAY
Thanks Bill

Surely someone knows what this is or does. I have one in the wiring harness, and thats what it is called in the wiring diagram in GM service manual but it doesn't mention it anywhere else.
Thanks Bill

I am pretty sure the TCS relay goes to a TH400. Is it an orange wire coming from the fuse box into the engine compartment?

Thank You for answering.
The TCS is on the firewall and has dark blue and tan wires
The LT V8Delay Relay is in the dash harness and has dark blue/ black/ tan
and are listed as circuit numbers 959 and901 but the service manual only lists circuits from 1 to 340. So far I got everything working except the key buzzer. It just annoying that I can't figure it out,Gm put it there for a reason.
Thanks Bill

Is it that relay under the dash mounted behind the glove box next to another relay of some sort? It may be the anti dieseling relay?

Yes it is under the dash. Why do I need a anti dieseling relay and how does it work or what does it control?
thanks Bill

Can't remember :o but it has something to do with the A/C compressor clutch circuit.

Dean is right. I know my 72 had that as well. I pulled all the A/C stuff out of mine though and remember cutting it out.

There is a guy that made a post named Grumpyschevelle that replaced his A/C portion of his harness on a '71 a while back and I looked at that thread a lot while I was monkeying with my A/C wiring.

see if you can search his name and find it?

Matt

The "LT V8 DELAY RELAY" is the 72 version of a "TCS" relay. The relay you have under the hood is the L6 TCS DELAY RELAY, should only be found on cars originally equipped with an inline 6. The V8 delay relay is under the dash mounted next to the glove box. Not to be confused with the delay relay and anti dieseling relay that are part of the A/C compressor clutch control, these items were installed on 71 Chevelles but may have been installed on some 72s. They are mounted between the firewall and glove box.

The V8 delay relay wires are- black, tan and dk blue. The black wire is routed to the Trans switch, grounds when in high gear auto or man. The tan wire gets power from the RADIO TCS fuse. The dk blue wire is routed to the TCS solenoid.

With the engine warm when the Trans shifts to high gear the delay relay circuit competes, after aprox 20 seconds the relay picks up completing the TCS solenoid circuit allowing vacuum advance. For the TCS circuit to work correctly all of the TCS components need to be in place and wired. Temp switch, Trans switch, engine idle stop solenoid, vacuum advance solenoid.

On a V8 there shouldn't be a firewall mounted delay relay. Could your engine harness be from a 6 cylinder car? If it is the wiring will not be correct for a V8.

Thanks to all for your response.
To Elree, you were exactly right, The wiring is as you said. I went back to the parts car, it is a V8 auto AC and it had a solenoid in the vacuum advance line and a throttle stop solenoid. Which had been disconnected and wires cut long ago by previous owner and the vacuum hose connected directly to distributer. They left the relay under the dash by the glove box.

Question
What does preventing vacuum advance untill the car is in high gear and warm, accomplish? Do I really need it?

Question
I have an Assemble manual and a GM Service manual, which manual shows air condition wiring diagrams because I can find nothing in either for AC.

To Elree This is the third time in four years you have helped me with this car and I really appreciate it, if I ever have the the good fortune to meet you, I'm buying.
Thanks Bill

"What does preventing vacuum advance untill the car is in high gear and warm, accomplish? Do I really need it?"

Somehow it was supposed to reduce emissions. You don't need it if it will pass your local emissions inspection.

The service manual should have the A/C wiring diagram. The second or third section of the manual covers heat and A/C.

The relays under the glove box are for " Anti Dieseling " on A/C cars. This is how it works. You drive your 71 with A/C ( on or off makes no difference)to a destination, When you shut the key off, BE VERY QUIET and listen.
The key is shut off and in your hand. You have just activated a relay that sends 12 Volts to the A/C clutch, This locks up the A/C clutch and puts a very big load on the engine to spin the A/C compressor.
With the A/C clutch engaged the engine will stop " Right Now "
With a standard transmission, The " Red Neck " anti diesel trick was to, Shut the key off and have it in gear then " Dump the Clutch "
This was G.M.s idea of a " Anti Diesel " system on the 71 A/C cars. As Paul Harvey would say (R.I.P.) " Now you know the rest of the story "
Bob:thumbsup:

The TCS is intended to keep the engine running with less spark advance which causes a higher exhaust gas temperature. The higher temperature tends to burn up unburned hydrocarbons in the exhaust. At idle, the engine in not making much heat, so any trick to raise the temperature was welcome. Once in high gear, the load on the engine is higher and more heat is generated, so more spark advance can be used. Of course, for a driving cycle that does not get into high gear frequently, the fuel economy will be poor.

Thank you all for the explanations
I have decided that the TCS is not going to be connected so that problem is fixed. Is dieseling a problem when you have AC on a small block ? I have had many small blocks over the years and never had a problem with dieseling but none ever had AC. This is my first experience with Ac on a restoration and after spending a couple of days installing the vents behind the dash, I regret the decision to go with AC. You do not need AC in Ohio as much as you do in Arizona
Bill