Cehbra

iTrader: (1)

Hi guys
I have finally collected all the parts to make the cowl induction hood functional on my base Firebird with LO3 TBI engine. I also found a vacuum port under the air cleaner that I can use to sense WOT. I teed a vac line and already successfully tested that with an OEM vacuum switch and an LED.
On the original diagram from the 83/84 LG4/L69 Trans Am the current goes through a temp sensor and an oil pressure switch before the vacuum switch. I believe this is due to emission reasons? Do I actually need to do this too?

Would my wiring diagram work the way I plan it?

OrangeBird

iTrader: (1)

No , your drawn incorrectly . The switched contacts of the relay are supposed to drive the hood solenoid and the vac switch is supposed to drive the relay's coil . The oil pressure switch is to make certain it sends the hood solenoid power only when the engine is running and the temp switch is to keep it from opening till the engine is warmed up . I will try to post a picture with the correct way .

Cehbra

iTrader: (1)

Hey thanks a lot for that answer! That's a cool idea - I didn't think of that.
My idea was to use the D+ current from the alternator via a relay so that I only have current when the engine is running. But if I understand you correctly you suggest to do the same thing via the originally intended temp/oil pressure switch?

OrangeBird

iTrader: (1)

Hi Cehbra ,


Yes , you are correct that you would only want it to function while the engine is running . Now , in it's original design , the oil pressure switch and temperature switch would serve the function of not allowing solenoid action till the engine was warmed up running . Well , If we're not being too picky about copying the original and just want it to work , my diagram will work when connected to key on power (like the big pink one going to the ignition coil , for instance) since usually just about any time the key is on it's because the engine is running . Granted , it will open any time the throttle is opened a good amount even with the engine cold , but if that is a factor the temp switch could be incorporated into the relay coil's circuit as needed .

Standard relay wiring always has the physical switch controlling the relay's coil , and the device to be controlled is connected to the relay's N/O or N/C contacts to provide the actual power to run the device .

Cehbra

iTrader: (1)

Alright! I think I get it, thanks! Any suggestion what temp switch could be used and where to mount?

OrangeBird

iTrader: (1)

Great , I'm glad to hear your set with it . As to the temp. switch I think I'd try my initial tests without it , and if it's found to be needed it would then get wired into the Coil circuit of the relay . Always remember a relay is just a switch the uses a tiny amount of current to switch a large amount of current , and so only controlled devices will attach to the movable contacts , while controlling devices will attach to the relay's coil*


* Except in the case of the "Self Holding Relay Circuit" of which the only one I know of on our cars is the rear defroster relay . In that case , one of the relay's multiple sets of contacts DOES in fact connect with the coil (and a timer) to hold the relay engaged for a specified amount of time after the button is pushed and released . This really has no relevance to our discussion of your hood relay but I figured if I made the blanket statement about the coil and contacts being separate entities that someone would have to come along with "But what about the self holding relay circuit ?" and so there ya have it