wiring question

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wiring question

Postby monzaaddict » Mon Feb 15, 2021 1:11 am

I have a 75 Monza with some butchered wiring that I am trying to correct. I have a 3961573 relay on the firewall which is not connected to anything. there is another generic relay spliced into the wiring harness. I originally thought the relay was for transmission controlled spark but the car is an automatic and does not have it. After looking through the wiring diagrams on this site, I see that the relay is for the choke pulloff. When starting cold engine i believe pumping pedal causes choke to fully close. The solenoid pulls choke open slightly so engine will run. The wiring diagram portion showing the relay seems to show the light green wire for the choke pulloff solenoid and the dark green/white stripe wire for the temp sending unit going to the same pin. Does that little angled line indicate in wiring language that the one wire goes to the pin behind or beneath the other??? what is the purpose of the relay? Right now the black wire with pink stripe is cut and taped off at firewall bulkhead. I am assuming at this point the black/pink stripe wire is not supplying power as it should from the fuse and needs to be replaced. It looks like they tapped into the wiper motor power wire. How do I determine the wire gauge (they are all pretty small to me).

According to diagram solenoid is normally closed. I tried opening relay and broke it so I cant verify this but it did click when power and ground were applied. There are three wires. black with pink is power, then there are light green which goes to choke pulloff solenoid and dark green/white stripe that goes to temp sender. How does this work?

I highlighted wiring diagrams below

the relay has 3 terminals and a short pin. What is short pin for https://www.ebay.com/itm/NOS-TCS-CONTRO ... SwcJhf23f0
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Last edited by monzaaddict on Wed Feb 17, 2021 7:29 pm, edited 7 times in total.
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Re: wiring question

Postby monzaaddict » Mon Feb 15, 2021 1:41 am

do I go by the amperage of the fuse controlling circuit to determine wire gauge?
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Re: wiring question

Postby monzaaddict » Mon Feb 15, 2021 2:03 am

I found this photo showing what I believe is the choke solenoid relay plug (with light green and green/white stripe wires) Not the wire being held. Same solenoid was used for tcs (transmission controlled spark) so it might be wires for that.
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Re: wiring question

Postby monzaaddict » Mon Feb 15, 2021 2:05 am

How do I test the relay I have?
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Re: wiring question

Postby monzaaddict » Mon Feb 15, 2021 2:52 pm

on the 74 wiring diagram the black/white stripe goes directly to the choke pulloff solenoid. Dark green goes directly to a 1 wire temp sender which appears to ground to block. Can I replace my 2 wire sender with the earlier 1 wire sender? What is the point of the relay on 75s?????
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Re: wiring question

Postby monzaaddict » Mon Feb 15, 2021 3:59 pm

Is the dark green wire from the relay on the 75 wiring diagram sending power to temperature sender or ground? It then goes to the temp indicator light which has a pink wire (isn't this power)?
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Re: wiring question

Postby monzaaddict » Mon Feb 15, 2021 4:01 pm

Can I just eliminate the relay and wire the choke pull off solenoid and temperature sender as shown in 74 wiring diagram?
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Re: wiring question

Postby monzaaddict » Mon Feb 15, 2021 5:17 pm

relay info
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Re: wiring question

Postby zeke » Tue Feb 16, 2021 9:43 am

Be aware that there are mistakes in the GM wiring diagrams here and there. Electric chokes draw a bit of current, use 10 or 12 ga
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Re: wiring question

Postby monzaaddict » Wed Feb 17, 2021 5:30 pm

It is not wiring for an electric choke. The choke is water heated on early vega 140. The solenoid is the pulloff that opens choke slightly when engine first starts cold.


Is it possible that the relay works as follows. The relay is normally closed with no power. When you first pump gas before cold starting choke closes fully. At start power is sent to through normally closed relay, to the choke pulloff solenoid which slightly opens choke so engine does not stall. As engine warms, the water choke further opens choke. As engine warms relay grounds to block through 2nd terminal on temperature sender. This causes relay to energize, breaking contacts and choke pulloff solenoid deenergizes. This was probably to eliminate the constant electrical draw from solenoid that wiring directly to solenoid would have caused in earlier wiring.
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Re: wiring question

Postby zeke » Thu Feb 18, 2021 10:00 am

Maybe the temp switch is a dual and one side controls choke relay at a lower temp while the other operates the temp light in overheat condition. Just a guess going by the info you provided here. The factory manual may explain the operation in detail.
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Re: wiring question

Postby monzaaddict » Thu Feb 18, 2021 10:56 am

Thank you that diagram gives more detail on the choke solenoid relay wiring.
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Re: wiring question

Postby zeke » Thu Feb 18, 2021 11:07 am

That diagram is the one you posted and I modified with my guess
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Re: wiring question

Postby zeke » Thu Feb 18, 2021 11:42 am

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Re: wiring question

Postby monzaaddict » Thu Feb 18, 2021 3:21 pm

Yep i just was looking at the same rockauto info last night. The sender is even marked r- likely for relay and g likely for gauge. Thanks.
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