The 1947 - Present Chevrolet & GMC Truck Message Board Network







Register or Log In To remove these advertisements.

Go Back   The 1947 - Present Chevrolet & GMC Truck Message Board Network > 47 - Current classic GM Trucks > The 1967 - 1972 Chevrolet & GMC Pickups Message Board

Web 67-72chevytrucks.com


Reply
 
Thread Tools Display Modes
Old 09-01-2020, 08:51 PM   #1
skkroosw
Registered User
 
Join Date: Mar 2017
Location: Winnsboro, SC
Posts: 3
Is this a bad coil?

Two issues could be going on here that are preventing this '69 c10 from starting while cranking. Pretty sure #2 is a problem, but also #1 could be going on.

1. I am not sure the test indicates a functional coil. I think there should be a resistance from the + terminal to the top wire leading to the distributor, but it tests open.

2. A wire may be missing at the coil. There are atleast two loose wires nearby, but I thought they've always been there loose. However, I think a resistance wire OR a wire+resistor from the ignition is needed to power the coil when the starter is not turning... BUT, the truck doesn't start so I suspect #1 is also a problem. I test no voltage on the coil (+) in the run position.

thanks!
Attached Images
 
skkroosw is offline   Reply With Quote
Old 09-01-2020, 10:05 PM   #2
BigBird05
Registered User
 
Join Date: Aug 2019
Location: Cheraw
Posts: 1,300
Re: Is this a bad coil?

You need 12v from the starter R terminal and 9 v from a ignition 1 source. So if you have only one wire on the + terminal on the coil you are missing a wire. Fix that first then move on to the next problem.
BigBird05 is offline   Reply With Quote
Old 09-01-2020, 11:01 PM   #3
CastIron
Registered User
 
CastIron's Avatar
 
Join Date: May 2013
Location: Oregon
Posts: 329
Re: Is this a bad coil?

If I remember correctly, there is only one wire attached to the positive side of the coil. The resistor wires goes from the bulkhead connector down to the starter, then a regular wire goes from the starter to the coil. You should have some voltage at the coil, but it may not be 12 volts, depending on whether the points are open or closed. I would start by checking the fuses first, and making sure they have voltage on both sides. Then check the large connector near the master cylinder. The resistor wire is usually a braided looking wire, so if you can find that measure from the large connector to the positive coil terminal. It should have some resistance, but not a lot. If it has no continuity, that is the problem.
CastIron is offline   Reply With Quote
Old 09-01-2020, 11:20 PM   #4
dmjlambert
Senior Member
 
dmjlambert's Avatar
 
Join Date: Apr 2016
Location: Cypress, TX
Posts: 3,859
Re: Is this a bad coil?

The resistor wire is a cloth covered wire that normally goes from the bulkhead connector into the tape-wrapped engine harness. Shown as 20W/OR/PPL on wiring diagram, but probably faded to white. Inside the engine harness it is attached to 2 yellow wires. One of the yellow wires goes to starter, and one goes to the coil. The engine harness is covered with tape up to the clamp at the rear of the engine at one of the transmission housing bolts. From there the yellow wires go to coil and starter. This is how it was on my 1969 truck. Since you have a blue wire perhaps you have some patched or replaced wires. Here is the wiring diagram and pictures.


dmjlambert is offline   Reply With Quote
Old 09-02-2020, 12:29 AM   #5
mr48chev
Registered User
 
mr48chev's Avatar
 
Join Date: Jul 2007
Location: Toppenish, WA
Posts: 15,705
Re: Is this a bad coil?

Well I learned something today.

As many of these trucks that I have worked on and as many as I have owned (3 running and driving) I never noticed that. If by chance the Orange with purple tracer wire runs directly to the coil you don't have the resistor bypass working.

I've run into other point igniton Chevrolets that do not have power to the coil from the switch when they are in start position relying on the resistor bypass on the solenoid to provide 12 V when cranking.

Here is a link to testing a coil https://atlib.info/blog/176-how-do-i...-ignition-coil

My regular go to ignition test procedure papers are out in the garage and it's too late to dig them out tonight.
__________________
Founding member of the too many projects, too little time and money club.

My ongoing truck projects:
48 Chev 3100 that will run a 292 Six.
71 GMC 2500 that is getting a Cad 500 transplant.
77 C 30 dualie, 454, 4 speed with a 10 foot flatbed and hoist. It does the heavy work and hauls the projects around.
mr48chev is offline   Reply With Quote
Old 09-02-2020, 06:31 AM   #6
racerop
Registered User
 
racerop's Avatar
 
Join Date: Jul 2015
Location: Laurel Springs, NJ
Posts: 94
Re: Is this a bad coil?

Quote:
Originally Posted by skkroosw View Post

1. I am not sure the test indicates a functional coil. I think there should be a resistance from the + terminal to the top wire leading to the distributor, but it tests open.

thanks!

This is the very definition for resistance



A coil should read a low resistance , so your multi meter needs to be on a small scale. But should read less than 300 ohm but more than 1 ohm


What do you mean when you say “open”

Last edited by racerop; 09-02-2020 at 06:37 AM.
racerop is offline   Reply With Quote
Old 09-02-2020, 08:58 AM   #7
skkroosw
Registered User
 
Join Date: Mar 2017
Location: Winnsboro, SC
Posts: 3
Re: Is this a bad coil?

Quote:
Originally Posted by racerop View Post
This is the very definition for resistance



A coil should read a low resistance , so your multi meter needs to be on a small scale. But should read less than 300 ohm but more than 1 ohm


What do you mean when you say “open”

By open, I mean the multimeter reads null on the 20 ohms and lower setting -- which means it is more than 20 ohms or even infinite \ open circuit. I wasn't quite sure how coil works, but I thought I saw testing online of 2-3 ohms from (+) terminal to distributor wire... and I don't get that.

THANK YOU for the replies so far. I'll investigate closer today and update.
skkroosw is offline   Reply With Quote
Old 09-02-2020, 10:04 AM   #8
LockDoc
The Older Generation


 
LockDoc's Avatar
 
Join Date: Aug 2006
Location: Montezuma, Iowa
Posts: 25,772
Re: Is this a bad coil?

Quote:
Originally Posted by CastIron View Post
If I remember correctly, there is only one wire attached to the positive side of the coil. The resistor wires goes from the bulkhead connector down to the starter, then a regular wire goes from the starter to the coil. You should have some voltage at the coil, but it may not be 12 volts, depending on whether the points are open or closed. I would start by checking the fuses first, and making sure they have voltage on both sides. Then check the large connector near the master cylinder. The resistor wire is usually a braided looking wire, so if you can find that measure from the large connector to the positive coil terminal. It should have some resistance, but not a lot. If it has no continuity, that is the problem.

You would be wrong on that. There has to be 2 wires to the coil. The resistor wire does not connect to the starter solenoid. The Yellow wires connect to the starter (R) terminal and supply a full 12 volts to the ignition coil while the solenoid is engaged. (cranking) When the key is released and returns to the RUN position the coil then gets power through the resistance wire coming directly from the ignition switch through the bulkhead connector to the coil.

LockDoc
__________________
Leon

Locksmith, Specializing In Antique Trucks, Automobiles, & Motorcycles

(My Dually Pickup Project Thread)

http://67-72chevytrucks.com/vboard/s...d.php?t=829820

-
LockDoc is offline   Reply With Quote
Old 09-02-2020, 11:43 AM   #9
kwmech
Senior Member
 
Join Date: Mar 2003
Location: Colfax-California
Posts: 8,630
Re: Is this a bad coil?

To answer your question, yes, you should have continuity
kwmech is offline   Reply With Quote
Old 09-03-2020, 07:51 AM   #10
custom10nut
Registered User
 
custom10nut's Avatar
 
Join Date: Apr 2015
Location: East Tn (In the heart of the Smoky Mtns)
Posts: 1,887
Re: Is this a bad coil?

SUV’s for future reference
custom10nut is offline   Reply With Quote
Reply

Bookmarks


Posting Rules
You may not post new threads
You may not post replies
You may not post attachments
You may not edit your posts

BB code is On
Smilies are On
[IMG] code is On
HTML code is Off

Forum Jump


All times are GMT -4. The time now is 04:03 PM.


Powered by vBulletin® Version 3.8.11
Copyright ©2000 - 2024, vBulletin Solutions Inc.
Copyright 1997-2022 67-72chevytrucks.com