On the 3 wire engine harness - there is the oil pressure and coolant sending unit wires and then the 3rd wire for the coil positive. That is the heavier gauge red wire with a light green trace and the yellow push cap for the coil connection. I am getting full battery voltage in both the key start and run position. Is that right? I thought all these cars used a resistance wire for run. If I have the full voltage off that wire all the time I will use that for my Pertronix II system and electric choke. Will save a few extra wires and relay. My wiring harness is a combination I made of 69.5 under the dash and 72 forward of the firewall.
With no load(coil) there is no voltage drop... The resistance only comes into play when it must pass current... Assuming points & they are closed, the voltage on battery side of coil should read 6-8v, points open full battery voltage... You can use the coil feed to trigger a relay that switches full 12v... That's how I have my Comet wired...
Cool ........ that makes sense now. No load, no drop ........ Yes, I intended to use that wire to trigger the relay. I was checking to make sure the power was there after I installed the harnesses and was surprised to see full battery voltage at all times. THANKS!
The feed at harness connector to coil travels around to the I terminal on solenoid... Since that connection will serve no purpose with the Pertronix it can be used to trigger the relay, plus it's a handy spot..
So, mount the relay next to the solenoid and use the "I" solenoid wire as trigger? That would clean up some wiring. I wonder if the stock coil wire would be sufficient to power the electric choke on the Holley? I don't think it would - plus it is not fused properly. Do you have an electric choke and if so, how did you wire it? Same feed off the relay as the coil?
Just doing some reading - looks like the place to go for the electric choke is the STA terminal on the alternator. That make sense so the choke doesn't get power from the key, but from the engine after it starts.
The aftermarket carbs have a 12v electric choke, the STA terminal supplies around 7v so choke opening will be lazy at best(my Cobra Jet is currently connected via this method)... I'm going to add a relay to feed choke & ign(same relay can easily handle both)... A fuse can be added to each line... I have a small Painless aux fuse panel mounted near solenoid on my Comet, includes a relay triggered by former coil feed at I terminal... It has three switched & four always hot circuits(or was it other was around?), all are fused... The choke, Ign & electric fan are fed from switched, while low beam headlights are on a always hot & high beam another... https://i1358.photobucket.com/album...less_zpsa452e924.jpg?hotlinkfix=1511735963599
wired mine from the key on, didn't think the three seconds to start would make that much difference...and didn't.
What are you talking about??? Three seconds from start?? Triggered from a relay would be no different...
I like the idea of being able to sit with the key in the on position and not have it effect the choke. But I see what you are saying that it works fine for you.
Tom, I did a little experiment today with the choke. At full battery voltage, the choke plate begins to open at 23 seconds and became full open at 65 seconds. Using the old coil supply resistor wire, the choke still began to open at 23 seconds and became fully open at 75 seconds. Not much of a difference. Watching the meter, voltage dropped down to a low of 9.6 volts about half way through the cycle and then started to climb again. Once the choke is fully opened, voltage climbed back up to 11.4 volts, and may have gone a little higher but I shut down the test. Not much load on that wire to keep the choke open. So I might just use that after all since it is already right there in the old coil feed. Just need an inline 10 amp fuse for safety. If I felt ambitious I could run it through an oil pressure switch that would cut the power to the choke when the engine is not running, similar to the safety switch for electric fuel pump. What do you think?
Apparently your choke element varies in resistance as it opens... As long as there isn't a major voltage drop in that ignition line, I'll guess everything will probably be OK... I know P-II & III state to use a relay if necessary for full battery voltage... Supposedly not necessary for P-I(what I have triggering a Crane Hi-6)... I'm currently finishing up a heater core install on my Cobra Jet, while I'm under hood I'm going to wire a relay from IGN & batt at solenoid for choke(thank you for starting this thread)... With choke connected to STA on alt, takes probably five minutes to come off high idle and that's with a very lean setting... Connected to battery via clip lead, time seems to be similar to your findings(yes I've had a clip lead hanging next to solenoid)... I try to keep it's under hood looking orig, appears I can mount relay directly under solenoid so will mostly be hidden by wiring to solenoid...
I wish the 302 block had an oil pressure port in the back like the 351C & 351/400M had. If so I would put in a pressure kill switch there that would cut power to the choke when the engine is not running. Right now I have both a mechanical gauge and idiot light senders off the stock port by the filter. Don't really want to plumb another port there for a 3rd switch. I have the new Pertonix relay installed for the coil 12v and will wire that choke up to the old coil feed today. Will get a nice run in tomorrow and let you know how it works.
Well this is interesting. I sent an email to Pertronix technical support, about hooking the choke to the + terminal of the coil. Here is what they replied: Eric, That would be fine. The big issue was most user didn't know the car had a resistor wire in the line. So, they didn't know coil positive wasn't a good 12-volt source because of the resistor wire. So, instead of holly trying to educate customers on how to correctly check for a 12-volt source with a resistor in line. It was easier for them to say don't use the coil positive then they didn't need to worry about it at all. In your case with the relay we know 100% you have a good 12 voltage source. So, you can use coil positive to power the choke with no worries. Your Pertronix Team, Marvin Grebow Jr.
The way that reads they are thinking you are installing relay??? I checked original coil hookup on the CJ that both powers Pertronix and "turns on" the Hi-6... Main power to Hi-6 is from battery... Anyway it read 10.07v and has been fine for over 15 years, with the relay added voltage reads 9.82v... These are static voltages with engine not running, no doubt will be 2-2½v higher with alt charging... I'll find out tomorrow...
