TC29: how I added glow plug button and sorted out timer relay

[tmeric7]

My TC29DA has cranked longer to start with the cold, plus some erratic behavior at the glow plug light. This post is to share how I worked though things.

I replaced the glow plugs in the process. For documentation, my New Holland P/N is SBA185366190. I paid $30 for eBay replacements and received NGK 6628 (Y-107V). When I removed the old, they were NGK 0424 (Y701RS). They appear the same. New ones had 1 ohm resistance. Old ones has 0.8 ohm. Maybe didn't need replaced, but small expense.

Glow plug button

When the key switch is turned to the ignition (on) position, the glow plugs run for 4-5 second on my model, controlled by a timer. I wanted a push button to add preheat time. I studied the wiring diagram, which I attached (bottom) but the pin number are hard to read on my copy and scanning makes it worse... sorry. Best to have your own if attempting. The glow plug power relay #3 sends current to the glow plugs and a micro-relay that powers the dash light. +12V comes into the relay for this purpose at pin 30 (HM4), and is there when the battery is connected. The switch is closed, sending current out pin 87 to the glow plugs (HM9) and the light micro-relay (HM99), by a voltage drop across pins 86 and 85 (left side of diagram). Turning the switch to "ignition" or "start" puts +12V at pin 86 (upper-right), so the glow plugs are triggered by sending ground to pin 85 (lower left). This is the job of the glow plug timer relay, and it does so under two circumstances: (a) for several seconds when pin 4,C is energized by "ignition", and (b) when pin 5,B is energized by "start."

I added a push button to operate the glow plugs without affecting any other function by splicing into (1) tan wire HM28 running into pin 85 of the glow plug power relay, and (2) into black wire HM12 running into pin 3,D of the glow plug timer relay.

There are many switches out there, but I used NAPA P/N STB6301. It seemed pretty durable, and matches my added NAPA ignition switch, P/N KS6600, as others have done.

Timer Relay

Aside from this, my glow plugs seemed erratic, and the timer relay (hanging down by the oil filer in the fist picture above) failed the bench test described in the attachment here:

TC29D glow plugs

Is there a way to test if glow plugs working? On cold mornings, 20s, sometimes warmer, tractor has trouble starting. The glow plug light only goes on when cranking. I set throttle to where I believe 1500 rpm will be. Cranks good, but puffs black smoke and won't start. I tried putting in gear and...

www.tractorbynet.com

(from the FSM)

So I waned to replace it... The New Holland P/N is 385870300 (superseded by ...301). The NGK model number on my unit it S81NF. A replacement from my dealer is $113, currently. If you search these numbers online, an attractive alternative (which sources claim is a substitution) pops up, NGK model number S81NL. I think it is for a few Kabotas, and it only cost me $18 on eBay! But, here is the catch... the timer function works fine: function (a) above, but it does not trigger the glow plugs when starting: function (b) above. I'm not the first to notice this. See post #5 from SG51Buss here:

Glow Plug Timer control units

The glow plug indicator lamp on my New Holland TC35 Boomer would occasionally come on, and now it just stays on. According to the helpful threads in this forum, the cause is a faulty glow plug timer unit...

www.tractorbynet.com

At this point I have my original unit which has an erratic timer but works in the "start" position and a pseudo-replacement that has a good timer but does not energize the plugs in "start". I confirmed all this with bench testing and checking voltage at the glow plug busbar on the tractor. My original timer still starts the tractor. The replacement won't. At this point I coughed up the $113 for the replacement from the dealer, and it performs (a) and (b) as it should and (most importantly) starts the tractor. In the picture below they are: original (left), cheap alternative that didn't work for me (center), and dealer replacement (right).

P.S. I feel the urge to clarify some poor wording in my FSM that seems to have confused/mislead some about the timer relay. Here is a snippet from my page 55-39:

Look at "This controller controls the glow plug indicator light only; it does not control current to the glow plugs." Think about that... So then what *does* control the glow plugs getting energy for a few seconds if not the timer?! Besides, if you review the wiring diagram, as I did, you see that the timer triggers the glow plug power relay, which energizes the plugs. So the timer does not send current to the plugs *directly* but it sure does determine when the power relay energizes them. Also, the label on pins 3 and 6 in figure 79 are switched. I won't post another picture, but I pulled the circuit board out of my original unit and the pins are labeled. They didn't have the best person proofing this section of the FSM!

I hope this helps someone! Cheers, Tristan

 

[tmeric7]

Here is a brief clarification and update on performance.

I mentioned that pins 3 and 6 are switched in figure 79 of the FSM (compared to the circuit board) in that last image I posted. This is true, and the text to the left "follows" that switch. Meaning that a user could follow those directions exactly and the relay would be tested properly. Problems would arise, however, if one compares these pinouts and their wires to the wiring diagram. Then you must realize that pin 3 is physically in the lower left. The bench test described in the first link in my original post is this same procedure from a different FSM that gets the terminal numbers correct (with letters). Sometimes the terminals are labeled with letters, sometimes numbers. A=6, B=5, C=4, D=3, E=2.

I used the tractor to clear snow from our recent storm. Temperatures were below freezing, but not far below. On turning the key to ignition, the timer ran the glow plugs for 4 seconds, as it should. I used my button to add 12 seconds to that before attempting to start the tractor. It fired up as if on a bright summer day! I did not use the block heater this time, intentionally, to see how this would perform. It's only one time so far, but I believe there was clear improvement.

 

[matt9923]

Thanks for the write up. I am having a problem with my Tc29D now as well. I have been running the cheaper $18 timer for years now with no issue even in cold. This year I cannot get it to start without multiple attempts at heating and starting the plugs.

I replaced the plugs and timer, still same hard start issue. I am not sure what would have caused a harder start now. I have to do a litter more troubleshooting to make sure the glow plugs are getting power for the 8-9 seconds the light is on. May need to add the push button as well, I just wish I had a good explanation for harder starting, I have had this tractor for years and never had issue even in the cold.

 

[tmeric7]

Your hard starting could be related to one of a few other things that are "aging out" and the problem is cropping up in colder weather because starting is generally harder in the cold. The list includes battery cables, cable ends, ignition switch, starter itself, and the "starter relay circuit."

There is a lot of information on all of these if on this site if you poke around long enough, but read up on the starter relay circuit. Essentially, the low current that triggers the starter solenoid needs to pass from the battery through the ignition, all the safety interlocks, etc. By the time it gets through this maze, it looses "oomph" with an aging tractor and can't trigger the solenoid. The solution is to add a relay with power directly from the battery that can flip the starter solenoid and is triggered by the current that used to flip the solenoid (hard) and now only needs to flip a relay (easy). No safety switches are bypassed. Much info is contained in the following thread (and others). My post #127 was an attempt to summarize my experience. Like you, my issues began with hard starting in colder weather, and this was the solution for me.

TC33D wont start

Thanks dada be Mine won’t start but your post helped me find the fuse Thanks again farm dog

www.tractorbynet.com

 

[matt9923]

Your hard starting could be related to one of a few other things that are "aging out" and the problem is cropping up in colder weather because starting is generally harder in the cold. The list includes battery cables, cable ends, ignition switch, starter itself, and the "starter relay circuit."

There is a lot of information on all of these if on this site if you poke around long enough, but read up on the starter relay circuit. Essentially, the low current that triggers the starter solenoid needs to pass from the battery through the ignition, all the safety interlocks, etc. By the time it gets through this maze, it looses "oomph" with an aging tractor and can't trigger the solenoid. The solution is to add a relay with power directly from the battery that can flip the starter solenoid and is triggered by the current that used to flip the solenoid (hard) and now only needs to flip a relay (easy). No safety switches are bypassed. Much info is contained in the following thread (and others). My post #127 was an attempt to summarize my experience. Like you, my issues began with hard starting in colder weather, and this was the solution for me.

TC33D wont start

Thanks dada be Mine won’t start but your post helped me find the fuse Thanks again farm dog

www.tractorbynet.com

Thanks, to clarify my starting system does work good. I am planning on replacing the battery as it’s getting towards 5 years old. I replaced the starter solenoid a while back and the ignition switch is new, have changed a couple. It turns over pretty strong, its like the glow plugs just aren’t heating up enough…

 

[tmeric7]

Gotcha. I once tested my glow plugs because I thought they may be underperforming. If you pull them and test the resistance, they should each be about 1.2 ohms, I think... just going off memory. But you replace them, so at least new ones should be good. To check to see if they are getting voltage, you can put the negative end of a multimeter on ground (or - terminal of the battery) and the positive lead to the glow plug bus bar. You should read about 10.5-11 V when the glow plugs are "on". Sorry if you already know all this. When I did these checks everything was working, so that's why I added the push button. I ignored the possibility of weak compression!

 

[matt9923]

Gotcha. I once tested my glow plugs because I thought they may be underperforming. If you pull them and test the resistance, they should each be about 1.2 ohms, I think... just going off memory. But you replace them, so at least new ones should be good. To check to see if they are getting voltage, you can put the negative end of a multimeter on ground (or - terminal of the battery) and the positive lead to the glow plug bus bar. You should read about 10.5-11 V when the glow plugs are "on". Sorry if you already know all this. When I did these checks everything was working, so that's why I added the push button. I ignored the possibility of weak compression!

The old glow plugs were old a couple years old but I was hoping new ones would help. Same but i will do some more troubleshooting and make sure all of the connections around the glowplugs are clean so there getting the right amount of current. I just ordered a switch, i like that idea and its way cheeper than the $120 timer that may not help much. I think we need to get in the habit of plugging it in in the winter also. I was thinking lower compression or dirty injectors/ lower injection pressure. But it runs good and does everything we ask of it. Has about 1700 hours on it if I'm remembering correctly.