Continuity check for single wire thermo switch

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cwill
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Re: Continuity check for single wire thermo switch

Post by cwill »

I was able to perform the low glow test by unplugging the solenoid wire at the solenoid. With the key in the start position, I got the same clicking sound from relay #1 and 0.00 volts at the buss bar. I had the red lead on the buss bar and the black lead on the neg. terminal of the battery.
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Re: Continuity check for single wire thermo switch

Post by cwill »

I did the low glow test by removing the wire on the starter solenoid. Relay #1 made the same clicking sound and I had 0.00 volts at the buss bar.
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Paul
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Re: Continuity check for single wire thermo switch

Post by Paul »

cwill wrote:
Wed Nov 23, 2022 5:04 pm
I was able to perform the low glow test by unplugging the solenoid wire at the solenoid. With the key in the start position, I got the same clicking sound from relay #1 and 0.00 volts at the buss bar. I had the red lead on the buss bar and the black lead on the neg. terminal of the battery.
Yes, relay #1 (the hi glow relay) will still click when you turn the key to the run position.

But, when you turn the key all the way to the start position, #2 relay (the lo glow relay) will click on and stay on (or at least it should) for as long as you have the key in the start position. This will allow current to flow to the glow bus through the glow dropping resistor. And you should see some voltage on the bus. I measured 3.7 volts on my truck with this test today.

So, you are getting 0 volts. This means that there is an open or a very high resistance point in the glow current circuit. You can track this down by leaving the lo glow circuit actuated (will need someone to keep the key turned to start) and then using a voltmeter to check along the black wire leaving the battery to the glow relays for battery voltage. And then, from the lo glow relay along the black/yellow wire to the bus bar.

Presumably, you will see 12volts at the battery, but will lose it at some point as you go along the wiring. This will give you a clue as to what device or wire is the culprit.

Give this a try.

Paul
'84 P'UP 2 wd diesel, 5 spd with 0.78 fifth gear and differential back to 3.73.
cwill
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Re: Continuity check for single wire thermo switch

Post by cwill »

Is the 'low glow' relay the same as relay #2? My relay #2 does not have the black wire with yellow tracer plugged to it. At the big spade of relay #2,closer to the fender, I have the black wire with red stipe that comes out of the dropping resistor. At the other spade, closer to the fender, I have the black wire with no tracer that comes directly off the pos. terminal of the battery. After the battery, it splits into two legs; one goes to the above mentioned spade of relay #2, and the other goes to the engine side big spade of relay #1.

As I do your test, I'll test the voltage of the wire at its plug connectors or termination places. I'm assuming I don't pierce any insulation to to these tests.
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Re: Continuity check for single wire thermo switch

Post by Paul »

Yes, the lo glow relay is ID'd as #2 on the wiring diagram.

I erred in my description of the lo glow wires and you are correct noting that the battery current wire leaving the lo glow relay is black/red. And, this goes to the dropping resistor and then the black/yellow wire leaves the dropping resistor and runs on to the the glow bus (through a couple of connectors).

I would do as you suggest, that is to probe the wire at the connectors or wherever it is possible without piercing. However, at some point you may want to pierce the insulation to pin down where the voltage is and isn't.

Paul
'84 P'UP 2 wd diesel, 5 spd with 0.78 fifth gear and differential back to 3.73.
cwill
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Re: Continuity check for single wire thermo switch

Post by cwill »

I did the low glow test for on the black wire with yellow stripe that feeds the glow plug buss bar. With the black wire with yellow stripe connected all the way to the buss bar, at the bar I had 0.0 V, after turning to start, I still had 0.0 V.

I followed the wire back from the buss bar to its first plug and unplugged it. I did the same test from that plug. Before turning to start, that plug had 12.6 V, after turning to start it still had 12.6 V.

I did the same test on the next plug downstream, and concluded by testing the spade at relay #1 where this wire terminated. The results were the same. 12.6 V before and after turning to start.
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Re: Continuity check for single wire thermo switch

Post by Paul »

cwill wrote:
Sat Nov 26, 2022 5:22 pm
I did the low glow test for on the black wire with yellow stripe that feeds the glow plug buss bar. With the black wire with yellow stripe connected all the way to the buss bar, at the bar I had 0.0 V, after turning to start, I still had 0.0 V.

I followed the wire back from the buss bar to its first plug and unplugged it. I did the same test from that plug. Before turning to start, that plug had 12.6 V, after turning to start it still had 12.6 V.

I did the same test on the next plug downstream, and concluded by testing the spade at relay #1 where this wire terminated. The results were the same. 12.6 V before and after turning to start.
Ah. When you disconnected the connector you spoiled the test as this opened the circuit and there was no longer a load on it.

Otherwise you did the right stuff. But, measuring 12.6 volts any place on the black/yellow wire when the key is not turned to start is confusing as voltage should appear here only with the key at start. When you turn the key to start the glow controller will very momentarily turn relay number 1 on and then off. This might have fooled you if you did not wait a few seconds for number 1 to turn off to take your measurement.

Do it over again but do not open any connectors. Access the voltage measurements by sticking a probe of some kind into the connectors and then see where it is that you are losing the voltage.

By the way, can you hear or feel relay number 2 operating when the key is turned to start?

Paul
'84 P'UP 2 wd diesel, 5 spd with 0.78 fifth gear and differential back to 3.73.
cwill
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Re: Continuity check for single wire thermo switch

Post by cwill »

I held both relays in my hands and when the key was turned to start, #1 clicked then #2 clicked then #1 clicked again. With the key returned to the off position, #2 also clicked again.

Regarding the voltage test while keeping the wire connected, I had 0 V at the buss bar with the key in the off and start position. At the first plug back, from each half of the plug I had 0 V in both key positions. At the next plug back, close to the fender, on the half of the plug closer to the buss bar, I got a reading from 0 to 8 to 9 V seemingly depending on how well the black lead of my meter was connected to the neg. terminal of the battery. It wanted to fluctuate. The current sensing resistor bar got very hot. The buss bar itself did not have a noticeable temp. change. Also, the plug that gave that voltage reading warmed up too, but didn't get hot. At the spade of relay #1 where the wire terminates, I had 12+ V in the off and start position, with no apparent effect at the resistor bar.

For all these voltage tests, i held the key in the start position for at least 4-5 seconds as I was playing with the leads to make the best contact.
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Re: Continuity check for single wire thermo switch

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cwill wrote:
Sun Nov 27, 2022 5:57 pm
I held both relays in my hands and when the key was turned to start, #1 clicked then #2 clicked then #1 clicked again. With the key returned to the off position, #2 also clicked again.

Regarding the voltage test while keeping the wire connected, I had 0 V at the buss bar with the key in the off and start position. At the first plug back, from each half of the plug I had 0 V in both key positions. At the next plug back, close to the fender, on the half of the plug closer to the buss bar, I got a reading from 0 to 8 to 9 V seemingly depending on how well the black lead of my meter was connected to the neg. terminal of the battery. It wanted to fluctuate. The current sensing resistor bar got very hot. The buss bar itself did not have a noticeable temp. change. Also, the plug that gave that voltage reading warmed up too, but didn't get hot. At the spade of relay #1 where the wire terminates, I had 12+ V in the off and start position, with no apparent effect at the resistor bar.

For all these voltage tests, i held the key in the start position for at least 4-5 seconds as I was playing with the leads to make the best contact.
OK, this is progress. The spade connector at the fender which seemed intermittent very likely is. Remember that the sensing resistor got hot when you disturbed the connector. The sensing resistor gets hot only when current is flowing to the glow plugs.

The spade connector, itself, warmed up because it has become an intermittent resistor. Not good. This connector is a problem and hopefully your only one. You need to either take this connector apart (which is difficult) and clean it or try to clean it by inserting some kind of polishing agent or stick into it. Sometimes, just pulling it apart and putting it back together several times will clean it pretty good. I like to use a little WD40 on it when doing this.

When you're done cleaning the glow system hopefully will work. If not, repeat the trouble shooting process to see where any other bad connections are located or if this one is still bad.

FYI: The bus bar does not get hot like the sensing resistor because it is made of a good conductor and has close to zero resistance, whereas, the sensing resistor is a 15 milli-ohm resistor and this is enough that with the high glow currents it will get too hot to touch. So don't try it.

Paul
'84 P'UP 2 wd diesel, 5 spd with 0.78 fifth gear and differential back to 3.73.
cwill
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Re: Continuity check for single wire thermo switch

Post by cwill »

I've cleaned all the plug connectors, that I see are related to the glow system, many times with spray electronics cleaner from the hardware store. What about eliminating that plug and joining the two ends together permanently.
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Re: Continuity check for single wire thermo switch

Post by cwill »

I had that plug apart and could not separate the metal spade and its receptor from their plastic housings without breaking the plastic. Both metal ends looked very clean and corrosion free. I still sprayed WD40 and worked the two ends together and apart repeatedly. I also bent the hooks down closer to the bottom on the female half of the plug. I put the two ends together, they fit together more tightly, and it started. I knew it right after I turned the key to charge the plugs. I couldn't hear that very audible clicking sound probably from relay #1. I am thinking that plug, even though clean, was not making solid enough contact to be a good conductor. If this ends up being the only problem, it was a long tour of the glow system for a simple fix, and I am grateful for the tour and your help. Thank you Paul.
~Chris
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Re: Continuity check for single wire thermo switch

Post by Paul »

cwill wrote:
Mon Nov 28, 2022 12:50 pm
I had that plug apart and could not separate the metal spade and its receptor from their plastic housings without breaking the plastic. Both metal ends looked very clean and corrosion free. I still sprayed WD40 and worked the two ends together and apart repeatedly. I also bent the hooks down closer to the bottom on the female half of the plug. I put the two ends together, they fit together more tightly, and it started. I knew it right after I turned the key to charge the plugs. I couldn't hear that very audible clicking sound probably from relay #1. I am thinking that plug, even though clean, was not making solid enough contact to be a good conductor. If this ends up being the only problem, it was a long tour of the glow system for a simple fix, and I am grateful for the tour and your help. Thank you Paul.
~Chris
Chris - -

You're welcome. I compliment you for sticking with the diagnostic procedure and reporting back.

I have not seen the connector get so loose as to not connect but apparently you have one there. Yes, you can just splice that together and get rid of the connector but I don't like doing that. I like to keep things as original as possible.

I have made some tools to separate the spade connector from the plastic housing and it is still difficult. If you were able to crimp the female part well enough you are good to go.

Paul
'84 P'UP 2 wd diesel, 5 spd with 0.78 fifth gear and differential back to 3.73.
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