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Starting Circuit for 73 Camaro


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jimd2p 
Member - Posts: 44
Member spacespace
Joined: January 24, 2005
Posted: November 23, 2010 at 7:13 PM / IP Logged  
Hi all. I am trying to recreate a stock start circuit on a 73 Camaro. What has happened is the original owner of the car put in an HEI distributor and a non-stock starter. When doing this, he added a toggle switch to put power to the distributor, and somehow eliminated the stock circuit. I tested at all wires at the ignition switch, looking for a wire that stays hot while cranking and running, but turns off when the customer turns the key off.
I looked at this relay set up:
https://www.the12volt.com/relays/relaydiagram52.html
but still don't what to use as a trigger.
Any direction you can point me would be appreciated.
itsyuk 
Silver - Posts: 505
Silver spacespace
Joined: February 23, 2010
Location: United States
Posted: November 24, 2010 at 9:19 PM / IP Logged  

ditch the relay....

there is the major bulkhead connector near the master cylinder that passes wires through the firewall to the engine compartment.

one of those wires inside the car is a 10 or 12 gauge pink wire and after it goes through the bulkhead becomes a little 18 gauge wire (i dont know which color it becomes) that originally ran to the firewall mounted resistor block and then to the coil.

get on some chevelle sites and ask around for someones OEM set-up from under the hood that they are replacing with an HEI upgrade. it should fit the camaro. pretty easy to install but it may not be in the same "hole" of the bulkhead than a chevelles. so that is why it is so important to know where your pink wire is o the inside of the car.

you also need to make sure your starter solenoid has the "I" terminal to run a wire to the coil from so the coil can have a full 12v while cranking ...

the wire setup from a chevy, olds will fit easily. pontiacs have the starter on the drivers side so some of them fit a little wierd and may need modified. buicks wont be a direct fit either since their dist is up front.

opgi may sell a kit to give you exectly what you want.

rotsa-ruk!

yuk

yuk
quiet rural missouri, near KC.
If your system moves you physically and not emotionally, you have wasted your money.
Custom_Jim 
Copper - Posts: 210
Copper spacespace
Joined: November 28, 2003
Location: Missouri, United States
Posted: November 25, 2010 at 8:50 PM / IP Logged  

Like itsyuk said, there is (or was) a factory wire coming out of the bulkhead connector by the brake booster/master cylinder. This section of wire coming out of the bulkhead connector between the bulkhead connector and where it would have connected to the original positive side of the coil was a resistance wire. This wire became powered when the ignition switch was turned to the run position and basically powers the coil when the engine is running and keeps the ignition system powered up. Being a point style ignition system back then this resistance wire dropped the voltage getting to the coil (and then through the points) to keep the points from pitting and wearing out prematurely. Since you need to power up the ignition system while the engine is cranking, GM back then used the "I" terminal on the stock started solenoid as an output to also connect to the positive side of the ignition coil. When the engine got cranked over the "I" output sent a full battery voltage to the coil to help the engine fire up and then once the engine started the coil no longer got full battery power from the "I" terminal on the starter but from the resistance wire coming out of the bulkhead connector.

Now depending on how far you are going to go, putting back in an original resistance wire would be the first step but if the non-stock style starter does not have an "I" output terminal then you need to either swap out the starter to the correct one or run some type of circuit to give the ignition coil a full battery voltage only when the engine is cranking over. You cannot use the "S" (solenoid) wire on the non-stock starter because if this is tied to the coil it would be then be fed with a slightly lower voltage off of the resistance wire and then the starter would not disengage when the key was turned to the run position. It may be possible to add a diode off of the solenoid wire to power the coil but I've never tried it.

If you cannot find an original resistance wire assembly for your car, you can put one of those clay style resistors on the firewall but if you are going for an original look, then this is not correct.

There's probably a salvage yard in your area that may have some donor parts you can get off of them. If not you may want to look around in some of the Camaro sites or their suppliers and see if anyone on those sites have what you need.

Jim

  

1968 Chevy II Nova Garage Find 2012
1973 Nova Custom
1974 Spirit of America Nova
1973 Nova Pro-Street
oldspark 
Gold - Posts: 4,913
Gold spacespace
Joined: November 03, 2008
Location: Australia
Posted: November 25, 2010 at 9:35 PM / IP Logged  
I find the above situation - and descriptions - confusing....
Normally HEIs - just like the IgnCoil - are powered from the ignition switch - specifically the IGN terminal which is on whilst cranking.
Cars that use external resistor coils - ie, a resistor or "ballasts" to drop 12V to about 8V - did so primarily for better spark. (Lower impedance for better response, and an ~8V coil for good spark even during cranking - ie, due to voltage drops.)
The resistor was bypassed during cranking to apply full system voltage to the IgCoil for a good spark.
(FYI - Although I changed my 12V IgCoil for an 8V IgCoil with external ballast, I never bothered with the bypass switch/relay; but I could have manually bypassed if needed.)
Most electronic ignitions do not need a ballast, but there are exceptions (and a few laughs!).
Modern systems tend to have current limiting so the type of coil is virtually irrelevant. (EG - my retrofitted reluctor and ignitor from a 1980s vehicle uses a 1.2 Ohm IgCoil (primary) but due to its current limiting I can use 0.3 Ohm primaries without a problem - except for erratic tacho readings!.)
FYI - I recommend at least an HEI or similar. I replaced my points after ~120kkms (75,000 miles) only because its block had worn down. Its contacts were still shiny. Thanks to the HEI (with its static dwell), the only time I gapped the points was when they no longer opened. I'd merely rotate the distributor as the timing retarded until the next re-gap - usually after 20,000 miles). Points substitution is trivial compared to taking the load off them!
FYI#2 - I was totally into CDI (Capacitive Discharge Ignition) and was about to build a simple, cheap, powerful multi-trigger/output CDI for sequential spark etc (only $2 per extra input/output) until I upgraded with that "stock" 1980s ignition system - its starts cold with a 5V battery! (Even my CDI may not have fired below 6 or 8V.)
Not that that has much to do with your wiring problem, but I'm wondering what was done & why, or why there isn't the normal IGN powered starter (switch) or ignition circuit.
But that sort of wiring should be simple.
I recommend however upgrading some vintage aspects - eg, alternator with internal regulator; modern fuselinks off or near the battery (eg - plastic types, not the old wire types); duplication of modern "Ignition" relays that not only take the load off the ignition switch but also provide polarity protection (ie, if the battery is connected R'se about, the relay(s) will not energise and hence any connected EMS, computer, audio, entertainment system etc will not blow).
Of course, it depends how original you want to keep it.
My everydayer is a 1965 ute. It has many retrofits, but it can be returned to original condition. (EG - I never cut original wiring; I'll make translator harnesses else bypass.)
   
jimd2p 
Member - Posts: 44
Member spacespace
Joined: January 24, 2005
Posted: November 28, 2010 at 7:36 PM / IP Logged  
Thanks all for the suggestions so far. The starter has been replaced and does not have the "I" terminal. As for getting the car back to original, I am not speaking to this as "period correct", but to work properly with the key.
I am assuming the original starter with the "I" terminal is what gave me the power while cranking, acting like a switched wire on a relay. The diagram implies that the ignition switch actually combines wires or circuits when being used, so that is what confuses me that I can't find the circuit at the ignition switch. I will dig in to the bulk head connector next to see what I find.
Thank you again for the guidance.
oldspark 
Gold - Posts: 4,913
Gold spacespace
Joined: November 03, 2008
Location: Australia
Posted: November 29, 2010 at 12:39 AM / IP Logged  
The starter's I terminal mimics the IgSwitch's Start position.
It can be done with a relay across the resistor the resistor to short/bypass it (ie: #30 & #87 to either end) which is energised by the Start signal - eg, IgSwitch STart to #86 & #85 to GND.
#86 could be connected to the starter solenoid instead (smaller wire).
Many cars us a 2-pole starter switch for this, ie the (IgSwitch's) start switch has one pole to the starter solenoid and one direct to the IgCoil-Resistor junction.   
FYI - the 2 poles else relay are required so that the 8V IgCoil does not back-feed power to the starter's solenoid or motor.

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