Simple (stupid?) caveman approach to manual glow

[sbachman]

Someone please stop me if I'm about to do something stupid. I read TDP's suggested approach to implementing a manual glow plug switch:
http://www.thedieselpage.com/members/features/manualglow.htm

Yet, it seems to me that there is a simpler solution. Why not just wire in a heavy-duty momentary switch directly across the high-current (copper) terminals on the glow plug relay? Assuming that an appropriate switch exists (which would handle the current draw of the plugs without arcing itself to death), this approach would apply battery voltage directly to the glow plugs and the indicator light, taking everything else out of the equation. I'm imagining two big wires with soldered ring terminals, connected to the two copper studs on the Glow Plug Controller and running through the firewall to a heavy duty push button switch on the dash.

Obviously, the operator needs to avoid leaning on the switch too long to keep from burning out the plugs. Also, this switch would be "live" at all times so I might want to add a second switch as a "safety" in the circuit to avoid accidental use (requiring both switches to be simultaneously pressed.)

Is this a dumb idea? Am I missing some obvious electrical issue? Thanks for any insights.
Steve

[Robyn]

A far simpler and safer setup would be to use a Ford starter relay to handle the heavy current and wire a low current push button switch to the dash to activate the relay.

Basically the early 6.2 used a similar relay but controled it with a timer unit that was temperature controled.

Easy to do and cheap.

best

Robyn

[sbachman]

Thanks Robyn,
Do you have a particular model/year or part number for the Ford starter relay? I assume this would be wired with the high current side in parallel with the Glow Plug Controller, across the copper stud terminals, correct?
Steve

[arveetek]

The glow plugs pull about 100 amps when engergized. You'd need a big, heavy duty switch, and large cables run into the cab. That's why a separate relay and remote switch with smaller wires is more desirable.

Casey

[DmaxMaverick]

I agree with Robyn. Use a Ford relay. Any year/model will work, get the cheapest you can find. There are other relays that will work, but the Ford relay is the cheapest (probably due to sales volume). If your current GP controller works, but timing is off, you can wire a low amp wire from a switched 12V source to the exciter stud on the controller, and let the controller relay carry the big amps (your finger/switch is the timer, then). Problem is, most of the time when folks are looking at this, the controller has failed, including the relay, and the controller relay is less reliable than the simple ford relay. You could just run a 10 ga. pair wire into cab and use a high amp switch to do the job without any relay. But, that's a lot of big wire, and the current drop may not get the plugs as hot as it should. The Ford relay, suitable switch, 14 ga. wire and connectors can all be had for less than 20 bucks, so there's no reason to not do it. 12' of 10 ga. wire, large connectors, and the heavy switch will cost much more that. I've had the Ford relay solution installed on my 85 for over 15 years with not so much as a hic-up.

Or.....
You could just fork over $50-80 for a new 85-93 glow plug controller and replace yours. It'll work in any year model or flavor of 6.2/6.5.

Also, the article you linked was intended to apply to later models needing extended glow times (automatic timed, with a manual option) for use on lower compression engines and AC60G glow plugs (which require a longer cycle than other plugs to get hot).

Much depends on your reason for needing to modify/repair your existing system.

[JohnC]

Anyone remember when you had to step on a pedal to engage the starter? Relays have freed us from huge, high current switches switches...

Besides, you wouldn't want those heavy wires running in the cabin...

[ronniejoe]

Someone please stop me if I'm about to do something stupid. I read TDP's suggested approach to implementing a manual glow plug switch:
http://www.thedieselpage.com/members/features/manualglow.htm

Yet, it seems to me that there is a simpler solution. Why not just wire in a heavy-duty momentary switch directly across the high-current (copper) terminals on the glow plug relay? Assuming that an appropriate switch exists (which would handle the current draw of the plugs without arcing itself to death), this approach would apply battery voltage directly to the glow plugs and the indicator light, taking everything else out of the equation. I'm imagining two big wires with soldered ring terminals, connected to the two copper studs on the Glow Plug Controller and running through the firewall to a heavy duty push button switch on the dash.

Obviously, the operator needs to avoid leaning on the switch too long to keep from burning out the plugs. Also, this switch would be "live" at all times so I might want to add a second switch as a "safety" in the circuit to avoid accidental use (requiring both switches to be simultaneously pressed.)

Is this a dumb idea? Am I missing some obvious electrical issue? Thanks for any insights.
Steve

The whole reason for doing this mod was to avoid buying a big switch or adding another relay and having to run the heavy gage wiring to support it. There is a perfectly good relay on the truck already. For about $5.00, you can have a few diodes and light duty switch for manual glow. It works.

But, do what ever your heart desires...

[6.5 Detroit Diesel]

I just got a heavy duty switch, 10 gauge wire, and then ran wires from on each side of the controller. Took a few minutes and no problems yet.

[sbachman]

Thanks for all the thoughtful responses. I see that there is a diversity of opinions and approaches. I'll likely go with the Ford starter relay. I still kinda like the simplicity of the Big Ol' Switch, but I see the potential problem with adding too much resistance to the high current circuit -- and, as suggested above, it may be cheaper/easier to find the Ford relay than an appropriate 100A switch.
I've ruled out the TDP method with the diodes and the harness modification. The directions don't apply directly to the 1993 6.5TD, and even if I figured out the appropriate modifications for 1993, I'm not really comfortable with modifying the harness. In the future, someone else might have the pleasure of working on this truck and they might get confused.
As one of you indicated, the most straight-forward approach would be to simply replace the stock part (Glow Plug Controller.) I'd do this if I was sure it is faulty, but it may be working as designed. The problem I'm having is that the glow plugs SOMETIMES don't come on when the engine or the ambient temperature are warm, resulting in hard starting. I've seen many posts which describe this same behavior, and some indicate that it is normal. Looking at the manual, it appears that there is no external "inhibit" device or other input controlled by temperature. So, I'm assuming that there is some thermal switch within the circuitry of the Controller itself. (Does anyone know if this is correct?) Anyway, I'm concerned that after installing the new Controller I'll still be wishing I had a manual switch in the cab...Maybe I'll replace the Controller and put in a manually controlled Ford relay too.
Thanks again.
Steve

[ronniejoe]

You're correct. The method in the article will only work on the electronic trucks -- 1994 and up.

[DmaxMaverick]

1993? you kinda' left out that part. In that case, you already have the best "stand alone" controller GM produced. There is no PCM in/output for the control. They are inexpensive (relatively) and easy to replace. They are also easy to modify for longer glow times. In addition, you can have a properly functioning automatic controller and a manual switch to operate the OEM relay at your whim. Simple and inexpensive to do. If your controller is working, there's no reason to toss it. Not now, anyway.

[sbachman]

Hi DmaxMaverick,
Sorry to be late with the 1993 info. (I thought I had set up a signature line with the truck specs. Oops.) Do you have instructions (or a link) for how the 1993 controller is modified for longer on time and/or activation at higher temperatures? I'm not sure I understand your last post. Did you mean the that the stock controller can be directly modified, or were you referring to adding the Ford starter relay as discussed earlier?
Thanks.
Steve

[gavin8or]

Hey there, I'm a '93 owner and proud of it. I'm here to ask how to do a manual activation, and to warn all others. I just went to do a compression test on my 93, and when I pulled out the glow plugs I found 3/5 have broken off their tips.

Question: does the '93 (or any other model) cycle the plugs while the truck is running? Other than that annoying 3 seconds that the light stays on after the engine has started.

Question: What's the best way to manually activate/deactivate the glow plugs? I wouldn't might having it run through the OEM controller, but I just want to be able to completely turn off the circuit the second the truck has started running.

Question: Does anyone have any information on lengthening the amount of time the relay timer normally keeps the glow plugs on? Also, what's the best way to turn the plugs on even when it's warm? I've found that sometimes the glow plugs will not even cycle, and I'm left hard cranking my truck during the summer months.

[daustin]

Hi there,
Yes the '93 is supposed to cycle the glow plugs after the engine is running if it thinks the coolant temp is low enough.
I've never seen any mod that would apply to turning the glow plugs off after the engine is running.
There are a couple of mods for the ODB-I trucks for the glow plug override, i think its on the Heath or Kennedy web site.
I would add a switch to the existing circuit to manually glow the plugs longer or when warm starting if i wanted to do that.
Also, the '93 trucks have the mechanical IP and have a rep of hard hot starting when the IP headspace gets worn and thus dosen't create a lot of pressure to the injectors on startup.
Hope that helps
Don

[gavin8or]

Don, a huge help thank you. I've talked with various injection shops that have mechanical IPs which are built to prevent the headspace from getting worn. So I am aware of that problem and the solution I guess.

I guess I'm going to have to read all the options which others have done, and make a plan and go with it. It makes me REALLY angry that I didn't listen to my friend when he told me to have a toggle switch to completely disable the whole glow plug relay, almost a year ago. He has done so on all his fords, but for some reason I figured that there was no way the plugs were turning on without the light turning on. I'm an idiot. Thanks for confirming what we both suspected as soon as we realized how badly my glowplugs had burnt off. I'm going to try some liqui-moly injector cleaner but probably it's going to take more work than that: those glow plugs really did a number.

[JohnC]

If the light works and it's not on then the glow plugs aren't on either. The light is powered by the switched side of the glow plug relay, just as the plugs are.

[NH2112]

Thanks Robyn,
Do you have a particular model/year or part number for the Ford starter relay? I assume this would be wired with the high current side in parallel with the Glow Plug Controller, across the copper stud terminals, correct?
Steve

Just pick up a 12V universal relay from NAPA, such as part number ST81. Some have a grounded base and some have to be grounded, but it'll work just fine. I use them on everything at work.