6066 (1960-1966) GMC Truck Club

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- Interiors, Dash, Lights and Electrical (https://6066gmcclub.com/forumdisplay.php?f=15)

- - No spark (https://6066gmcclub.com/showthread.php?t=50084)

Thank you all for the suggestions! It won't be long and i have it running (I hope). Yes I've been reading a lot lately that people are switching to pertronix so I'm definitely going to look into this. But for now I'm going to do what Ken wrote:-)

Checking meter. It's 12 but when cranking it goes to .18. I have black meter probe on the pos side of battery and the red to the pos of cool. Is that right? I did set gap on points also.

Quote:

Originally Posted by GTS61 (Post 67550)

Checking meter. It's 12 but when cranking it goes to .18. I have black meter probe on the pos side of battery and the red to the pos of cool. Is that right? I did set gap on points also.

The Red lead goes to the positive side of the coil. The Black lead goes to ground or battery negative. With the starter cranking the engine the voltage should be close to battery voltage (9-11 volts with a good battery, starter will create a large voltage drop during cranking). With just the ignition switch in the run position it should be near battery voltage (12.5-13 volts) with the points open. If the point is close the voltage will drop because the resistor wire (between the coil and the firewall connector), is use to prevent burning up the point while the engine is running. Once the engine is running the voltage will vary somewhat with rpm due to the amount of time (dwell) the coil is passing current with the points closed.

The .18 volts you have is the voltage drop from the battery through the starter solenoid and out the solenoid "I" terminal to the coil.

Thanks James!! I'm such a knucklehead when it comes to engines.

Just remember black wire on a meter or a truck battery is negative only. Red wire on meter or truck battery is positive only. Otherwise you will damage truck or meter. At this point, you need a mechanic or friend to help that has experience.

The starting system is set up such that when the starter draws a big load from the battery during starting, as James says, the coil is supplied direct voltage also. But after starting, the coil has a secondary/resistive circuit that provides reduced voltage to save "wear" on the points during driving. You should have two wires going to coil positive. I was just trying to find out if this system was maybe miswired so that little or no voltage was being sent to coil during starting, thus no spark. But when not cranking, and switch was turn to on, it shows 12V at coil.
James has spelled out that very well. This may not be the problem, just needs to be checked out like the points gap and rotor and condenser and firing order does. Because according to you, you have a no spark condition. It's going to be the ignition wiring, the coil, the timing or inside the distributor.

These are checked one at a time. We all would have our work cut out for us if we were doing it and we have experience. You have no experience and it is not possible to do these checks over the internet without some knowledge. You need to read, watch YouTube and take a community college class to get up to speed or it will take many years to get the knowledge and mechanics ain't cheap. Use the internet. I know you are using it here but we can't find the problem without your hands. We can't train on how to use a meter and then train how to troubleshoot. We can't train the entire ignition system, timing, point gaping...etc. Maybe a member lives near you and will help. I do have a lot of patience and want to help. That is what this site is all about but I see a big problem with synergy.

The reason you need two wires to coil (your possible problem), the need for a "12V to coil" check, before cranking and during cranking, and a visual inspection of the coil positive wiring, is described below:

One wire to coil comes from the starter solenoid "R" terminal and it provides 12V to coil while starting. It is only live when ignition switch is in the start (spring loaded/far right) position. It shuts off when you let go of switch. That is when the second wire takes over. This is the other wire that should be on the coil positive post. It is the resistor/resistance wire. It comes from the ignition switch when the ignition switch is in the "run" position or "on" position. It has a reduced voltage of only about 8-9 V. It's a "special" wire material and a specific length. It is wrapped back and forth on itself inside the harness bundle.

If you are missing the "R" wire from solenoid, then the other wire may not provide enough spark because as the starter needs all 12V. This wire, with only 8V, may loose more and not supply hot enough spark, thru coil, to plugs.
If you are missing the resistor wire, you won't have ANY voltage to coil after you let go of starter. If you were missing this wire, the truck should start and then die after you let go of switch. SOoooooo if you are missing the "R" solenoid wire or one of these two wires is mis wired to the wrong place, OR IGNITION SWITCH IS MIS WIRED, that could be the problem. So study the schematic and trace each wire to see where it goes AND SEE THAT THEY ARE STILL CONNECTED TO WHAT I SAID.
Not yelling, emphasizing.

Also the negative coil wire goes to the distributor, be sure that is wired correctly. That wire goes to the points pinch post, same place the condenser wire goes.

Where does the negative battery cable go? To somewhere on the motor?

Do you have a white ceramic block on the firewall anywhere? Like This?

Ignition switch wiring: Terminal marked "BATT" = wire directly from battery.
Terminal marked "Start" or "Sol" = goes to "S" terminal on solenoid.
Terminal marked "IGN" or "ON" = goes to coil pos. Again, some of this wire is the resistor wire.
These wires may go thru connectors or be passed thru junction blocks but do go where I indicated, eventually.
The ignition switch has a "ACC" terminal for accessories. The wire should go to the fuse box.
Some of the terminals I've listed on the ignition switch may have other wires connected to them. Try to determine that they are not interfering with anything we are doing.
Take your time, you have a lot to absorb and think about, but you are smart and none of it is difficult, just new to you. Eventually we will trace down the miswire, broken wire, bad component, adjustment error, missing wire, missing part.
I still don't know if you disconnected a wire during A/C install, or didn't install points correctly, did some other "work" you forgot you did or you didn't do anything wrong.

Don't take this the wrong way but I don't know what you know: You do know that when you check the spark plug it is out of the hole with the wire still attached and the MOTOR IS CRANKING OVER and you look for spark snapping/arcing across the gap at the threaded end, every revolution, Right? It has to be touching the unpainted, not greasy part of the motor. With all the coil and distributor wires hooked up.

"I did find a bad connection on the starter that I fixed." EXPLAIN this in detail!!!!! Answer ALL questions. underlined to enable us to think it thru. Not as interrogation or blaming.

The bad connection on the starter was the positive side of the coil going to the starter. The wire connector broke off from the wire at the starter. METER READINGS: I got a 12 on the meter with the black on the battery ground and the red on positive side of coil with the starter cranking the engine. With the ignition switch in the on position the meter reads 12 and drops to 5.6 when the points close. I do have 2 wires coming off of the positive side of coil, one goes to the starter (that I repaired) and one goes thru firewall that I'm having a hard time getting to because of my new ac evaporator but I'll find it tomorrow also I'll have to look at my ignition switch next. I do not have a white ceramic resistor on my firewall outside or inside of cab.

Quote:

Originally Posted by GTS61 (Post 67580)

The bad connection on the starter was the positive side of the coil going to I do not have a white ceramic resistor on my firewall outside or inside of cab.

It may be a resistor wire from the coil to the firewall connector.

Hook a wire (jumper) from battery positive post to coil positive terminal and see if it starts or fires using starter switch. Don't disconnect or change anything. Be prepared to disconnect the jumper in order to stop motor. Do that before checking switch. Do that next thing and report.

Make sure you have put everything back together before you do this test. If it does not fire, do the same test again looking at one spark plug gap. Don't have the plug near it's hole and do it in darkness. Again be prepared to pull off the jumper. See if you have spark.

I see James has commented while I was typing. That second wire, as he says, is probably the wire that goes to the Ignition switch. If you know how, you can disconnect it at coil, take ignition switch out of dash and let it hang, find the "on" or "run" terminal, take wire off that terminal. You do not want to take a chance that this wire has voltage. Both ends loose, do a continuity check (ohms). After setting meter to ohms, touch one lead to the detached coil wire and the other lead to the detached run wire and see if there is a reading. Most digital meters read zero when there IS continuity and read 1 or OL when there is no continuity. Does not matter what color meter lead is on what end of wire. Some meters will buzz/beep if there is a connection, so set to buzz if you have it. Do this after the above start test is done.

I did hook a wire from the positive coil to positive battery and nothing happened. After that I ran a wire from the second wire that was on the positive side of coil that goes inside of cab thru the engine connector, then took out ignition switch and hooked the meter (on ohms) to the wire that was connected to the IGN. The meter read 0.18. Shouldn't it read 0?