glow plug serial killer needs help!!!

[1980 hj47]

ive got this hj47 with a 2H, and baffling glow plug trouble. i have a manual "wilson" switch to glow the plugs that i have used for about a year. the truck is a 12v aussie model. i replaced the plugs with NGK 1229 10.5 volt plugs. i was only able to glow the system once, for about 10 seconds. and the truck started instantly. the next day all 6 glowplugs burnt out, no continuity. any ideas? the busbar sees 12.6 volts. does there need to be a resistor?

it looks like NGK makes 2 different 10.5 volt plugs... 1229 (Y1o7R) and 7493 (Y147T), anyone know the difference?

i am not using the controller, and i have 10.5v plugs, so, at 12v the 10.5v, 7 amp plugs should pull about 8.5 amps? about 50 amps total at 12v for 6 plugs?

[cruiser_guy]

You NEED glow plugs rated at the voltage you plan on giving them. Going to a "Wilson" switch generally means getting different glow plugs of a higher voltage rating as the OEM glow system operates at a lower than battery voltage.

Take a glow plug into a diesel shop and see if they have the same plug with a 13.5 - 14 volt rating.

[1980 hj47]

i would love to get a 14v plug for my 2H 12v system!! does anyone know if that works? can i use a 14v plug intended for a 24v vehicle? i can try the bosch plugs if that will work.

i had read in these forums that people are using 10.5 volt NGK 1229 in their wilson switch, 12v setups. what could i be doing differently?

[Henry James the 47th]

Hmm, something is clearly out of whack with your glow system.

The voltage of the glow plugs depends upon the type of system you have, 12v./24v. etc.

The original set up for your rig used no timer, 8.5v plugs, and a in-dash glow controller, which is essentially like having a 7th glow plug, itself wired in series to the plugs, which are wired in parallel.


With the modifications you have done, IF you are still using a controller on your dash, then you need 8.5v plugs. If, on the other hand, you have removed the controller from the system, you are back to an effective array of 6 glow plugs, and the 10.5v. plugs are the correct ones in that case. The higher the voltage, the lower the resistance. With the 10.5 v. plugs installed, it should result in a 15~30 second 'slow' glow cycle.

However, that said, if you used 10.5v plugs with the controller, the plugs would still work, however the glow warm up interval would be very slow indeed - like 45 seconds or so. If you use 8.5v plugs with no controller, you need to be cautious about over-glowing, as the 8.5v plug+controller set up is designed to bring both plugs and controller to 'hot' in 12~15 seconds.

The 14v plugs, which are used in non-Superglow 24v. set-ups, would be way too slow for your application, if they even worked at all. That's the wrong solution.

Sounds like something else is going on if you've fried all your new glow plugs in such short order. It sounds like your plugs have either glowed way too long, or they are perhaps grounding out somehow, or somehow getting 'too much current'. and "too much current" is more than likely a short somewhere that keeps all the plugs from evenly sharing the glow relay's output, and instead it is trying to glow only 3,4, or 5 of the plugs - thus the current would be too high at each plug.


Does the glow relay make an audible click when you actuate the glow system? What glow relay are you using by the way? Does the hot lead from the glow relay go directly to the glow plug bus bar? Is the bus bar in good shape?

Could you post some pictures of your set-up?

[Henry James the 47th]

One more thing: are you sure the glow plugs you installed are 10.5v?

The voltage rating is usually etched into the side of the glow plug body. The 10.5v NGK glow plugs that I bought last month are part number 7493 or Y-147T (old designation), not 1229. I'm not sure what the 1229 are exactly, in terms of specification. By the way, I picked up these 10.5v plugs by mistake, as I use the 8.5v plugs in my HJ47 -if you're looking for replacement plugs, I'll sell mine for $12/ea. They have been glowed for 40 seconds total.

[jabxyz]

Originally Posted by Henry James the 47th

The original set up for your rig used no timer, 8.5v plugs, and a in-dash glow controller, which is essentially like having a 7th glow plug, itself wired in series to the plugs, which are wired in parallel.

Henry James, Would the in dash glow controller be wired the same in my BJ40 with a wilson switch? If so I think a light bulb just went off in my head as to why my glow controller won't glow.

[Henry James the 47th]

It could be, depending upon how you have the manual system set up.

The 'switch' part is simple, in that it only activates the glow relay, whether it is controlled at the ignition barrel or by a momentary push button on the dash, OEM set-up or otherwise.

If you are using some variant of a manual system like that, then you could choose to use the glow controller or not. If you use it, since it becomes part of the overall current draw with the glow plugs, i.e., like an extra glow plug in the circuit, your glow plugs need to be matched to that. If you don't use the controller, then you need the voltage of plugs to suit that set up (and it's a higher voltage than the plugs used in tandem with a controller).

On a 2H, with 6 plugs and a controller, the correct glow plug voltage is 8.5v. Without the controller, the correct voltage would be 10.5v. This is for 12v systems.

I'm a little less certain when it comes to the B series of engines, however I have seen glow plug voltages listed for the B/2B/3B ranging from 8v on the early 1974~'75 trucks (which I'm pretty sure employed a glow controller), 8.5v for 1975~'80 (also with a controller). When the controller was dropped from the system in late 1981 or 1982 (most markets), the glow plugs went to 10.5v and they employed a timer in the system. Or, in the case of 24v. BJ40/42, Toyota went to Superglow in late 1981, which uses 14v. glow plugs.

For HJ45, the plugs are 8v up until 1974, then they are 8.5v after that, similar to the BJ40, and identical to early HJ47.

In my case, i went initially with 10.5v plugs, but when paired up with my controller, the coil in the controller only began to glow, feebly, after some 45 seconds, so I realized that the plug voltage was too high. When I swapped in the 8.5v plugs, the controller came on nice and red after 12~15 seconds, and didn't fry out after holding the key on for more than 30 seconds. So i think is is pretty safe to experiment like that, so long as you don't throw the plugs in that are for the Superglow system. For 12v Superglow, the plugs are 6v, and for 24v systems the Superglow plugs are 14v. If you popped those in there, trying to make it work like a slow glow system would likely result in a few burned out plugs or controller.

Personally, i really like the controller as it is a totally obvious and intuitive way of tuning into what is actually happening at the glow plugs, and that makes it superior to idiot lights of various forms, IMO. It does require that the operator have an interest in tuning in to how the engine glow cycle is operating, so that makes it a poor choice for those without such interest, and I'm sure Toyota went away from the controller in a search to make the system more simple/user-friendly (not sure that is the best term), along with desires to meet emissions targets and so forth.

hope the above clarifies more than it confuses!

[1980 hj47]

so if a 24v truck with a superglow system supplies 12v to the glowplugs, and if the glowplugs are 14v, why cant we use 14v plugs in a manual 12v system on a 12v truck?

isnt 12v on a 24v system the same as 12v on a 12v system?

[lostmarbles]

I think the safest thing for you to do is to make sure everything on your vehicle is matched the way the Toyota engineers did it originally on your vehicle.

And I would have thought 14V plugs on a 12V cruiser would be unable to glow at all no matter what you do - But I suspect that they would draw a lot of current in "trying to glow".

You say you have no "glow controller". So I assume you just apply 12V power to all 6 plugs (wired in parallel) directly via a simple switch? That switch would have to have a high current rating if you've done away with the "glow plug relay" - because Toyota used that relay to enable the "low-current-rated ignition switch" to safely switch the high glow plug current.

If you do try 14V plugs, I certainly don't think the plugs will be harmed this time round. But you could become a "wiring loom serial killer". He he.

[lostmarbles]

Originally Posted by 1980 hj47

so if a 24v truck with a superglow system supplies 12v to the glowplugs, and if the glowplugs are 14v, ......

I can't find who said that a 24V superglow system supplies 12V to 14V plugs


But reading back to your first post - I see you ask whether there is supposed to be a resistor. Well on mine the "glow controller" (that coil of wire that glows on the dash) is wired in series with my parallel-connected glow plugs. So that works just like a resistor and drops the voltage to my plugs. As shown here:



While I've never personally seen an "all manual system without any form of glow controller or any other form of automatic control" - It appears (from reading posts here) that other people have done this before and that your original 10.5V choice of plugs was correct. Are you sure they didn't fail because your Wilson Switch jammed "on" without you being aware of it? (Such an event is one of the hazards of not having any dash-indication to show whether your plugs are energised or not.) And I don't really think the 14V plugs are a good idea.