choke wiring again

[Hersbird]

Ok so I did a search and saw the previous responses on this. My car is now a bit different then stock. I have a pertronics style electronic conversion so my ballast resistor has a shunt so the coil gets 12v all the time. I also have the alternator wired normal 1968 with one field but there is an unused spade terminal on the back. I would like to use either the coil + or that unused alternator terminal for simplicity. Is one better then the other or are they both unacceptible?

 

[BillGrissom]

Hopefully your coil doesn't get 12 V if the ignition switch is off or your battery will run down. Hopefully you also have an Ignitor II or III, since I understand that the original Ignitor requires that you keep the ballast.

The "unused" terminal on the back of your alternator needs to be used, i.e. connected to a good ground. The factory did that by leaving out the ceramic insulator and bolting the spade to the frame, a sometimes iffy connection to corroded aluminum. If you have a later "square-back" alternator, with 2 isolated terminals, you need to run a jumper from one to gnd. Ditto if you have 2 isolated terminals on a round-back alternator (not the way they ship). With your 1968 alt wiring, the other terminal gets a variable voltage (0 to 12 V) that is adjusted by the regulator to control the field current and thus the output current. If still the old mechanical Vreg, it is actually switched on & off. Regardless, it isn't a steady source of 12 V ignition power.

 

[67Dart273]

If your alternator is using the 69/ earlier style regulator, you indeed need to ground the second field terminal, and there is no switched 12V to the alternator in that case

The short answer (no pun intended) is if you are using no ballast, you can hook the choke to the coil.

One thing I ALWAYS recommend to you guys is to check the wiring harness as well as the regulator ground, along with checking charging voltage.

To check the harness, turn the key to run, engine off. With your meter set to low DC volts, hook one probe to battery POS (starter relay stud or battery post) and hook the other terminal, in this case, to coil + (no resistor)

You are hoping for a VERY low reading, the lower the better. Anything more than about .3V (three tenths of a volt) means you have a voltage drop problem in the harness.

Next, warm up the engine (regulators change voltage with temp) and get the battery "normalized." Check charging voltage which should be near 14V, IE 13.8--14.2, in no case below 13.5, and in no case above 14.5.

You can also check the regulator ground by the voltage drop method

With the engine running at a good fast idle, and your meter on low DC volts, stab one probe on the battery NEG post, and the other directly to the mounting frame of the regulator Be sure to stab through any rust, chrome, etc.

Once again, you should read a VERY low reading, the lower the better, zero volts is perfect.

I would put an inline fuse between the coil and the choke. THE IGNITION feed (dark blue) coming from the IGN switch through the firewall is NOT fused!!!

 

[Hersbird]

Ok i looked again at the alternator and it isn't a 2nd spade like I thought but just a plate that must be grounded to the body like you described. The coil isn't getting all the time 12v from the battery, it is just bypassing the ballast resistor so it gets 12 in start or run. So I will check for voltage loss as you describe but am going to go with the coil + then. If I have too much other loss then I'll shore that up another way. How big of a fuse for the choke?
And yes I have the ignitor II

 

[67Dart273]

Choke fuse, not sure, I can't imagine it needs more than 5A. They were originally not fused, but the "more stuff" that is unfused makes me nervous. I've been around a few cars with burned up harnesses!!!

 

[BillGrissom]

Sounds like you have a good handle on the issues now.

I agree with 273 on the fuse. If you really want to know the current draw of the choke, measure the resistance from its power lead to gnd (or return lead if it has one). I = (12 V)/R, where I <> amps and R <> ohms. As the choke heater heats up, the resistance will increase and the current decrease. A good rule is to get a fuse rated ~3x the normal current.

Is this an aftermarket choke, like an Edelbrock carb, or the late 70's - 80's Mopar electric choke? I put the later (~82 Diplomat) on my 65 small block w/ the thermal sensor that comes with it. I didn't use a fuse, but since that was suggested ...