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Re: '63 GMC 305 Starts but won't stay on
RSchanz #1328141 Sun Sep 29 2019 08:23 PM
Joined: Jun 2012
Posts: 1,729
S
Shop Shark
Good tips from all. This has been a good read. Electrical is scary? No need to be. Frame and sheet metal is ground. Wire is how things get connected. So why 2 wires on the + on the coil? one is "run" from the key switch. That can be from a 6 volt source, a resistor wire, or a ballast resistor. The resistor wire cuts 12 volts down to 6 volts. The ballast resistor does the same thing. The ballast resistor can hide. It can be on the firewall, or inside the coil. Inside the coil is just a simple way to get a so called 12 volt coil. So why all this fuss about 6 or 12 volts at the coil? Simple actually. The points are a switch. That switch was designed to work with about 4 amps of power. The coil was made to work with those 4 amps. and...the condenser was too. When cars and trucks changed to 12 volts. The engineers could see no reason to change the coil, points, and condenser. Tha accountants would not pay for it any way. So an inexpensive resistor was the fix. Wire, ballast, or inside the coil. Same cheap and effective result. 4 amps at the points. The second wire on the +? That is from the starter. Foot or solenoid. It is to help with cold starts. Temp push of extra current to make a big spark. Off when the starter is off. simple and effective. So you have two simple tests. Test 1: key on in the run position. Volts at the + . 12 volts? you have a 12 volt coil(the one with a resistor inside) . 6 Volts? You have a ballast resistor or a wire resistor. Just a note: the points need to be closed. If they are open the circuit you are testing will be open. Volts reading will be funky. As in not useful. A ground strap is helpful to get past the rubber in the motor mounts remember ground is...the frame and sheet metal. Test 2: Volt meter at the + and turn on the starter. 12 volts? All is good. Let the key spring back, and 6 volts? If you have a resistance wire or a ballast resistor, all is good. 12 volts? If you have a "12" volt coil. All is good. Did you check to see if you have a ground strap? Most ground straps go from the motor/bellhousing to the frame Some(not many but some) just jump over a motor mount to avoid that sneaky bit of rubber. So what can go wrong? Runs in start(starter on) and quits when in run. Bad resistor wire(covered in previous posts). Bad ballast resistor(also covered in previous posts). Bad coil? Not this time. The coil works with the starter. Bad ignition switch? Not this time. Again covered in previous posts. Bad ground strap? Maybe. bad connection on the "run" wire? maybe. That is a start. look at the easy stuff first. Cheap is good. Let us know what you find.
Steve


Steve H
Re: '63 GMC 305 Starts but won't stay on
RSchanz #1328399 Tue Oct 01 2019 04:49 PM
Joined: Sep 2019
Posts: 23
R
RSchanz Offline OP
New Guy
Wow, really getting some great information from everyone. Learning more than just how to fix this problem but also some historical things as well.

I'm out of town for the week but right before I left I cleaned up the ignition coil and cleaned the connections going to positive and negative. The resistor wire is the cloth covered wired correct? Attached is an image. The wire didn't look like it was in great condition as you can see. I want to trace the wire as I feel like the work the mechanic did on the gas gauge might have been what created this.

At any rate, stand by for more updates next weekend.

Attached Files
IMG_8532.jpg (358.74 KB, 150 downloads)

The new guy

'63 GMC 305, 4 on the floor - farmer Frankenstein edition
Re: '63 GMC 305 Starts but won't stay on
RSchanz #1328415 Tue Oct 01 2019 06:35 PM
Joined: May 2005
Posts: 7,535
B
General Purpose
This post is getting too long. Let's wait until you do the work, do the test mentioned and answer all the questions. We are getting nowhere.
The resistance wire will probably have a large diameter cloth covering. White'ish or yellow'ish?

The other wire is green.

Nothing is cleaned yet that I see.


Watch out for careful drivers!!!
I'm away on an ego trip. Will be back on Feb 30.
I'm not an Auto Mechanic, but I play one on TV.
I charge $0.02 for every opinion and I take Paypal.
Plan B is always better than plan A, by definition.
You can't teach a new dog old tricks.


Re: '63 GMC 305 Starts but won't stay on
RSchanz #1328462 Wed Oct 02 2019 12:44 AM
Joined: Mar 2019
Posts: 1,072
G
Shop Shark
That's a mighty big glove you have there...lol

Re: '63 GMC 305 Starts but won't stay on
bartamos #1332721 Wed Nov 06 2019 04:20 AM
Joined: Sep 2019
Posts: 23
R
RSchanz Offline OP
New Guy
After a long hiatus because of work and lack of time I got back into it today and tested a few things.

When running your test bartamos with the circuit tester grounded to NEG on the battery and key in "ON" position I touched the + terminal on the ignition coil and got nothing. When having a friend try to "START" the vehicle it lit up.

After this test I left the key in the "ON" position and checked the starter. The light test only lit up when I touched the large 12v wire in the middle.

I also checked the wire that runs into the distributor from the ignition coil. With key in "ON" position I took the distributor cap off and with the circuit tester grounded to the NEG on the battery I connected the light to the center of the distributor and got nothing. Oddly, after removing the wire and when doing a continuity test I found that this wire didn't work. I went across the street to the mechanic and got another wire - tested this for continuity - it worked. Still engine didn't stay running. I attached a picture of the inside of the distributor cap because I think it could be replaced regardless.

I'm thinking I will start tracing the red wire in the ignition harness and make sure all of it's connections are clean and solid. I think I will also do the same for the resistance wire.

As always, any input is appreciated!

Attached Files
IMG_9147.JPG (253.63 KB, 87 downloads)

The new guy

'63 GMC 305, 4 on the floor - farmer Frankenstein edition
Re: '63 GMC 305 Starts but won't stay on
RSchanz #1332820 Thu Nov 07 2019 02:28 AM
Joined: Mar 2010
Posts: 9,450
5
Master Gabster
. The resistance wire must be energized when you come off of the start position on the ignition switch. Turn the switch to the on position and test voltage of the resistance wire at the coil.
While the ignition switch is in the start position, a separate wire is energized, providing full battery voltage to the coil.
If your resistance wire is bad, the engine will fire while the ignition switch is in the start position. Once the ignition switch is allowed to fall back to the run position, the engine will die.

Re: '63 GMC 305 Starts but won't stay on
RSchanz #1332852 Thu Nov 07 2019 01:03 PM
Joined: Jan 2013
Posts: 1,663
S
Shop Shark
On my 64 GMC, there is a toggle switch that somebody has put in, in the past. Its purpose was to jump a wire around the ignition switch to keep the ignition alive because the faulty switch would quit from time to time, but also would keep the engine running all the time when the switch was turned off too. I will be replacing the switch one day to fix this. Dont know if this pertains to you or not, but my .02 worth.
I might add also, my latest acquisition, a 1964 GMC 305 long bed, comes to me with a few electrical gremlins. First thing I will do before any trouble shooting is to check to see if it has its engine ground straps as well as body ground straps and will also add a hood to body ground strap for the park and turn signal lights in the hood that seem to be working off and on, more off though.

Steve

Last edited by sstock; Thu Nov 07 2019 01:11 PM.

1953 Chevrolet 3100
261 cu inch, sm420, 3.55 rear, torque tube still,omaha orange, still 6 volt, RPO green glass, side carrier spare, all done
https://www.youtube.com/watch?v=Bli...n05i04t1aokgm4p04jiwgffwhyyih5xbk0h00410
1964 GMC 1000
305 Big Block V6, sm420, the next cab off restoration
Re: '63 GMC 305 Starts but won't stay on
52Carl #1333124 Sat Nov 09 2019 06:29 PM
Joined: Sep 2019
Posts: 23
R
RSchanz Offline OP
New Guy
I see, that would explain why it lights up when in "Start". I suppose I should just replace the resistance wire and see what happens?

I'm going to inspect all the ground straps also because I know there is other electrical issues with the truck including a bad ground somewhere.


The new guy

'63 GMC 305, 4 on the floor - farmer Frankenstein edition
Re: '63 GMC 305 Starts but won't stay on
RSchanz #1333129 Sat Nov 09 2019 07:57 PM
Joined: Mar 2004
Posts: 4,683
M
Shop Shark
Checking grounds is always a good place to start!

Mike B smile

Re: '63 GMC 305 Starts but won't stay on
RSchanz #1333131 Sat Nov 09 2019 09:13 PM
Joined: May 2005
Posts: 7,535
B
General Purpose
When you did the test for 12V by touching the coil positive terminal with key "On", and did not get voltage. Obviously that tells you that you are not getting voltage to the coil. This is your only problem. You have no other problem. You don't have a ground problem. Your problem is very simple. You need voltage when ignition switch is at the "ON" position.
SO............start testing for voltage, with switch "ON", follow the wire at the coil positive and follow the wiring step by step, connector by connector, terminal by terminal, wherever it leads, all the way to the ignition switch until you find 12V. Report. One of the two wires will go to the starter, follow the other wire. The long waits between reports is making this last WAY TOO LONG. You are bouncing all over the place and blogging a lot of non info. DO the test I just gave and find out why the ignition switch is not providing voltage.

A section of the path between the ignition switch and coil positive is a resistance wire. Other sections will be regular wire probably.

A battery hot wire comes to the ignition switch and the ignition switch distributes that voltage to various places. (start, run, gauges, accessories)There may be a fuse panel and fuses involved and there may not. Just follow the wire backwards to the switch and see if the terminal on the switch for "ON" is live or not when switch at "ON". This, as I said long ago, is VERY simple. The testing of the wire from coil to distributor is an example of you going off on your own and proved nothing. STOP taking things apart. STOP disconnecting wires. If you want help, follow instructions. As Hot Rod Jerry says......"we don't guess, we test".
With all due respect, you asked because you don't know what you are doing, so stop doing what you don't know. The Cavalry has arrived.
I still don't see cleaned wires and how they are attached to coil and where they go. I know where they are supposed to go. I have a GMC and have wired it.


Watch out for careful drivers!!!
I'm away on an ego trip. Will be back on Feb 30.
I'm not an Auto Mechanic, but I play one on TV.
I charge $0.02 for every opinion and I take Paypal.
Plan B is always better than plan A, by definition.
You can't teach a new dog old tricks.


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