No Power to Coil

[DreamRyder1963]

I'm working on my brother's 69 and it has no spark. Well I pulled the cap and found the points burned so I replaced them and the condenser. It still did not have spark so I checked the power coming from coil and found none, so I replaced the coil. Still did not fix it. So I checked for power going to the coil. This is where it gets strange. I checked it Thursday and it was getting 12v then I rechecked it a bit later and it had 0 v. I replaced the end going to the coil because it was barely attached and then it had 5v. I have now replaced the entire wire coming from the harness on the firewall and found that it only has 8v coming out of the firewall and 12v going in the firewall. This leads me to believe that either the fuse box or the switch is absorbing a lot of power. I checked the continuity of the switch and it seems to be fine. How likely is it that the fuse box is absorbing the voltage? The battery is also putting out 12.8 v.

[1972BlueC20]

I believe your not supposed to get the full 12v until you go to crank it. I'm new to this, but I just had a similar issue this last weekend. My truck was running but was running rough since I bought it. I did a complete tune up on Saturday and it would not start afterwards. I was getting no spark to the coil or any of the cylinders. I suspected a wiring issue too as I wasn't getting the full 12v at the coil with the key in the run position. My uncle and his brother came to help the next day, and it turns out the points were not set properly causing no spark. We installed a points eliminator setup (pertronix ignitor # 1181) and then got it timed correctly (it was also off timing) and it fired right up. It's never ran so good as it does now with being properly timed and with all new ignition parts and the electronic ignition replacing the points and condenser setup. Even if you don't want to do the points eliminator, just getting the points properly set will work too.

I'm not sure if the problem I had is what your problem is, so wait for confirmation from another more experienced member of the forum before you do anything. But like I said, I do believe that your not supposed to get the full voltage at the coil until you actually crank it over. You may be having an issue with the points which is causing the no spark issue.

Hope this helps somewhat.

[DreamRyder1963]

The points are set a .016" so they should be fine. I watch the points while my brother cranked it and the opened and shut but did not create a visible spark.

[CCCC]

Ign circuit resistor reduces V to coil until engine spin/run mode.

Try breaker points gapped at .019. Gap has to be right to enable V buildup in coil. Try #1 fire at 8 degrees BTDC with no vac.

Process of elimination. With engine spinning, check for input V to coil, then check spark from coil wire to top of dist., then from dist to plug wire, etc.

If plugs are so poor that they do not fire well, upstream spark can look weak.

Hope this helps.

[DreamRyder1963]

I will try the points at .019". Should the readings vary so much even when its not in the start position?

[kwmech]

Put the test lamp on the pos side of the coil. Have your brother turn on the key, voltage? yes? have him crank it, lamp gets brighter? yes, put test lamp on neg side of coil, crank engine, lamp flashes? yes, you should have spark.
Put test lamp on pos dies of coil. Have your brother turn on the key, voltage? no.... oops check ignition, you will have a voltage drop after the firewall block, this is where the resistor wire starts. Got it fixed? voltage yes, crank engine jumps to 12v no, check yellow wire at the starter at the R terminal, repair wire. Wire goes to 12v now, good. Disconnect wire on neg side of coil, have voltage there with wire disconnected? no? replace coil. Hook up wire crank over, no voltage or flashing lamp, check point gap, make sure they are opening AND closing, still no flashing, check condenser and ground wire on the advance plate

[DreamRyder1963]

Originally Posted by CCCC

Ign circuit resistor reduces V to coil until engine spin/run mode.

Try breaker points gapped at .019. Gap has to be right to enable V buildup in coil. Try #1 fire at 8 degrees BTDC with no vac.

Process of elimination. With engine spinning, check for input V to coil, then check spark from coil wire to top of dist., then from dist to plug wire, etc.

If plugs are so poor that they do not fire well, upstream spark can look weak.

Hope this helps.

I reset the points to .019" and now they are sparking. It now has bright white spark going to the plugs. Now the just need to replace them and it should run.