It is not the grid heaters

[RTRAM]

The ambient temperature was 45 and the battery voltage was 12.6 before I started the test.
I disconnected the grid heaters and started the truck. The voltmeter went right up to the top end of the normal range or about 14 volts
With the headlights and fan on, the voltage stayed at 14 based on the dash board voltmeter.
I took the truck on a 20 mile drive at highway speeds. The voltage stayed at 14 for the drive
When I got home, I reconnected the grid heaters, restarted the engine and voltage was at 14 on the instrument panel. At this point, I measured with the digital Fluke and the battery was 14.6 and the alternator was a t 14.8.
Driving the truck again, the voltage on the instrument panel stayed at 14

Thank you for your patience.

 

[petersonj]

Good job! Thank you for the details. That is exactly what I wanted you to do. The results of your test drive strongly indicate that the charging system is working as it should.

When I got home, I reconnected the grid heaters, restarted the engine and voltage was at 14 on the instrument panel. At this point, I measured with the digital Fluke and the battery was 14.6 and the alternator was a t 14.8.
Driving the truck again, the voltage on the instrument panel stayed at 14

This indicates that the grid heaters did not pre cycle and post cycle due to the engine operating temperature being above the threshold for the grid heaters to operate. This is normal and the charging system is still performing as it should.

At this point I would load test the battery. The test is easy to perform using the starter for the electrical load. You will need a helper.

1. Disconnect the grid heaters
2. Disable the fuel system so the engine won't start
3. Connect your multimeter to the positive and negative battery posts (Note that I said "posts", not cables)
4. Have the helper crank the engine over for 15 continuous seconds. Voltage should stay well above 9.6 volts while cranking.
5. Let starter cool for 1 minute and repeat test 2 more times (let starter cool for 1 minute between tests).

Battery voltage should stay above 9.6 volts while engine is cranking. Starter motor should maintain normal cranking speed during all three tests. I normally would just do 2 tests, but since winter is approaching, you need to know if you have a healthy battery.

If the battery fails the load tests (or marginally passes them), then it needs to be replaced. If it passes the load tests easily, then I would be looking at the grid heater post cycle pattern.

- John

 

[RTRAM]

What is the best way to disable the fuel system?

 

[petersonj]

I am not very familiar with the First Generation trucks, but I believe there is a fuel shutoff solenoid right on the injection pump. Just disconnect the solenoid and try to start the engine. Should just crank and not start.

- John

 

[RTRAM]

We followed your instructions. The starting voltage was 12.3. After 15 seconds it was down to 9.1. After the cool down period is was back up to 12.1. I asked my wife to turn the key again and she said she was. The meter still said 12.1 and there was not solenoid clicking that I am used to with a dying battery. I have to assume that the battery is so dead that it doesn't have enough juice to even activate the solenoid to draw power from the battery which is why is stayed at 12.1? I have never had a battery so completely dead.

A new battery is on the list the next trip we make to town. Hopefully someone will have a group 31 with posts.

Thank you for your knowledge. I will let you know the outcome after the new battery is installed.

Again, thank you for you patience and wisdom.

 

[petersonj]

We followed your instructions. The starting voltage was 12.3. After 15 seconds it was down to 9.1. After the cool down period is was back up to 12.1.

This definitely sounds like a failing battery, Good job with the first test.

I asked my wife to turn the key again and she said she was. The meter still said 12.1 and there was not solenoid clicking that I am used to with a dying battery. I have to assume that the battery is so dead that it doesn't have enough juice to even activate the solenoid to draw power from the battery which is why is stayed at 12.1?

Is it possible that your wife was not depressing the clutch pedal far enough to allow the starter to crank? I would have expected the engine to crank over, or attempt to crank, or hear a clicking of the starter solenoid along with a voltage drop on your meter. Might be worth another test.

I think the battery does need replacing, but I would also like to see the proof by completing the final two separate 15 second cranking tests.

- John

 

[RTRAM]

Not sure of what happened. I replaced the battery just due to age and winter coming. The starter won't crank. The headlights come on, the heater fan works, the flashers work but it will not crank. I checked the wiring under the dash for the clutch and it is connected. I also got the car out and jumped the battery but that didn't give me anything. No clicking either. Whatever happened the other day when we were testing using the starter seems to be the issue.
Any thoughts??

 

[petersonj]

I was gone for a couple of days, so no reply from me.

Without an electrical diagram, I can only make general suggestions. I would check the fuse panel to be sure that all fuses are operational. There is probably a starter relay in the circuit and there is the clutch switch that I had mentioned before. And, of course, there is your ignition switch as well.

The fact that you don't get any action at all indicates there is an open circuit somewhere. If you can get access to jumper the starter relay (bypassing the ignition switch and clutch switch), that could point you in the right direction.

- John

 

[RTRAM]

I do have the shop manual and am starting at the battery and working my way back through the wiring. Thanks for your input.

 

[BigPapa]

Pretty simple circuit. From what I’ve read, your charging and starting systems are functioning as they should. Your issue is your grid heater. What part of the grid heater system is the problem is what you need to find.

 

[RTRAM]

I traced the starter problem back to the ignition switch. I tried the relay and that worked so I backed up and pulled the ignition switch and was able to hot wire the truck and got it running!!!. Now, I just have to find an ignition switch. Then I can get back to so if the grid heaters are working correctly. Thanks

 

[petersonj]

All right! Progress...

- John

 

[RTRAM]

Some years ago, I knew two master mechanics. Both of them seemed slow at the time (I was in my 30s). Now, I understand, they had patience and logic. The one could usually determine the source of an electrical problem in one cigarette. I lack patience most of the time.
Thanks for your help and patience.

 

[BigPapa]

Isn’t this what you need?

https://www.rockauto.com/en/moreinfo.php?pk=43985&cc=1086218&pt=4700&jsn=464

 

[NIsaacs]

Napa has it in stock if you want it quick. I find it strange that the switch quit at the same time as the battery exchange. Make sure all the small wires are attached at the positive battery post and that the connections are good. The 1st gen has several.

https://www.napaonline.com/en/p/ECHKS6557?impressionRank=1

 

[RTRAM]

I got an ignition switch from the local parts store. I installed the switch. NO change. With the new switch installed, the halo light comes on but it will not start using the key. From the diagram on page 8D-27 in the manual, I can start the truck using the center wire #4 and jumping to #2, then to activate the starter, I jump from #4 to #1 and the truck starts. The truck will still run with only #2 and #4 connected. If i hot wire the truck, the alternator only goes to 12.0 volts. On page 8D-25, the manual refers to Group 8M for Key-In-Switch and Halo light diagnosis. Unfortunately, my factory manual does not have 8M. Does anyone have that? It would appear to be the ignition switch but at this point in time, I don't know what to look at. Any ideas are very welcome. Thanks

 

[BigPapa]

Here’s an OE diagram of the ignition switch. This is from Alldata. I don’t have a manual so I don’t know what’s on 8M.

 

[AnonEd]

I have a 92 print manual and it has no 8M...goes from 8L Lamps to 8N Rear Window Defog. BigPapa's image above is the same as my print FSM (page AD10).

 

[BigPapa]

I had a CD manual I got with the '92 I had but gave it to the fellow that bought my '98. I still have a USB thumb drive he gave me. I'll have to see what's on it.

 

[RTRAM]

I was trying to find some more info. On your wiring diagram of Oct 29, I was trying to understand it. what does the NCA mean? also, what are the big blue boxes? Is there a testing routine for the grid heater in the manual that I cannot find? thanks