HOW TO: install a manual glow plug button

I was asked to create this guide after posting in the GP 101 thread. I had to rip my dash all apart just to take some pictures (okay, I also had to figure out how I did it the first time )

Specifically, this guide was done on a 1998 Beetle - it has the 2 wire glow plug setup . Obviously, if doing this to a Jetta, the dash removal will be a bit different. Enjoy!

Manual Glowplug Button.pdf

Update: if you have a car with a 4 wire glow plug harness, this mod will not work.

nice work on the write-up.

why do you want this feature?

I did it because for some reason, my glow plugs would not come on. My light would flick on for a second when the key was turned, but go off right away. And this is in winter in Ontario - my plugs SHOULD have been coming on but weren't. I went through everything - glow plugs (good), harness (good), relay (good), fuse on battery (good), etc. AND I was getting no CEL. Instead of easter egg hunting, I decided a manual button would be the best way to go - I know exactly when the glow plugs are and aren't working.

second tom's comment ?? you can increase the glow plug time and make it come on @ higher ambient temps easily with a Vag-Com so why do want to have this feature ???? Be carefull not to run them too long as you will kill the battery and can damage the glow plugs .

Yes, you'll notice that in the guide I advise against using a switch - you'll forget about it and leave them on. A button is best - hold for a few seconds before starting, release, start, and forget about it.

The combination senders for the temperature gauge and ECU aren't on your list of "everything". Were they omitted from your list of things replaced, or might it have been omitted as a thing you considered replacing?
This is a known issue in which the ECU sender in the unit fails, leaving the ECU thinking the coolant is warm enough to not require glow plugs. The second sender in that unit continues to send a proper signal to the instrument cluster gauge.
A simple test: Electrically unplug the sender. The open temperature sender circuit will be interpreted by the ECU as a very cold temperature and the glow plugs would come on and remain on for about 20 seconds. If the plugs work with the sender unplugged there is a well identified solution: Replace the temperature sender unit.

Are you referring to the temperature sensor? I'm assuming those two words are interchangeable (sensor and sender). I haven't checked that - I think it's working correctly because I have the hot start issue. If the engine is cold then the car starts up immediately (indicating the sensor works because the fuel map changes). If it's hot, it cranks for a while. I'll check it anyway, thanks for that!

why would you go to all that trouble and expence to install a solenoid when you could just run a ground to the glow plug relay from a switch. two light guage wires and you are done.???

or replace the temp sensor so the system operates as designed

To an extent you are right and you have a good point. What I've done here is definitely overkill, but doing it this way, I can have complete confidence in knowing that my glow plugs are getting power. It eliminates both the temp sensor and the relay as potential failures in the system and acts as a parallel to the relay, not a replacement. If the relay was called to operate, it would. But it never does.

And as I said, I don't believe my temperature sensor was the root of the problem. BUT, I have not checked it so I can't be sure about that.

But this solution gets the glow plugs working, which is my main concern. I need to know that they're working, especially with our winters. I could spend a lot of time hunting down the problem, doing diagnostics, etc., or I could spend 3 hours and do this. Just different ways to approach the problem.

Just a small update. I talked with my father about a bunch of this stuff, and he is positive that when I first got the car (and starting it was very hard, hot or cold) we replaced the temp sensor. I have absolutely no recollection of this, but he remembers it vividly, so I'm trusting his memory - he even says it came in the mail (and I probably ordered it from TDIparts.com).

Anyway, it made no difference when we switched it.

Secondly, my hot start issue seems to have evaporated. Recently I changed my timing belt, cleaned my intake, and removed, cleaned, and lubed the starter. Since doing all three, the car seems to be starting as instantly in the hot as cold. The biggest change I have noticed is after cleaning the starter - and there's no more squeal.

Anyway, enough of my particular car issues. This was meant for people who, for whatever reason, wanted to put in a manual glow plug button and weren't sure how to go about it. Thanks for all of your input

I had a similar issue that prompted me to install a manual over ride button in my prior Passat wagon. I was using the first generation (BK series) ECU from a 1996. The BK did not have the adaptable programming (mentioned in post #4) to skew the onset of glow operation at a warmer temperature as the later ECU do.
I also ran high percentages of biodiesel that really needed that added heat assist on cool mornings.

But I used the same factory glow plug relay. I only added a small, low amperage, normally open, momentary contact push-button switch and used it in parallel with the factory relay coil input from the ECU. The high current output circuit to the glow plugs remained unchanged.

I mounted my switch in the steering column near to the ignition switch. I could turn the key to the run (pre-start) position and press my override switch with my ring finger to force the glow plugs to ON, whether the ECU thought they were needed or not.

My current A3 conversion has a newer ECU that has the adaptation. I have it set to start the glow plugs at somewhere around 60F (15C) or colder.

Of course both of my (and your) versions do NOT show that the glow plugs are working. For that there is the need of an indicator showing the output. A simple 12 volt indicator lamp visible from the operator's seat, in effect a 5th filament, wired into the output side of the relay(s)will suffice to show that.

Lug_Nut said:

Of course both of my (and your) versions do NOT show that the glow plugs are working. For that there is the need of an indicator showing the output. A simple 12 volt indicator lamp visible from the operator's seat, in effect a 5th filament, wired into the output side of the relay(s)will suffice to show that.

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No that would only show that you have current on the output side of the circuit. you would need an amp meter on the output side to show the current draw of the glow plugs as they functioned ( or not ).

chaloux. just wait till one of those uninsulated and unfused leads you have on the solenoid contacts a ground. you will not believe how quickly you will burn up the wires under you dash and possibly the entire car

chrisfiat said:

chaloux. just wait till one of those uninsulated and unfused leads you have on the solenoid contacts a ground. you will not believe how quickly you will burn up the wires under you dash and possibly the entire car

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Yeah I'm aware of the consequences. I wrote in the guide under the "general picture" (about half way through) that things look much tighter than they actually are. And I also said that you want to double check everything and make sure it's tight. And finally, I said if anyone feels any level of discomfort about their setup, apply electrical tape liberally.

I've had this under my dash for two years and it has been trouble free. When I took my dash apart, I double checked all of the connections and everything is great and tight.

I appreciate the concern though, and other people should definitely be aware of the possibility of unwanted contact being made.

the whole point of the solenoid it to give you a remote way of controling a high amp load AND to provide the shortest pissible current path to the load ( glow plugs, starter motor etc) in order to do this the solenoid should be located as close as possible to the load ( this is why the starter solenoid id on the starter and not some where else) and controled remotely by the much smaller low current switch leads. this gets the solenoid out from under the dash and in a much safer area like the engine bay. and reduced the run length of the high current wires so as to provide as much flow s posssible to the load. Another good reason to remove this thing from under the dash

This system is a parallel of the factory system. It does nothing but give the driver the ability to manually activate the glow plugs.

If what you're saying about the location of the solenoid is true, they should have put the 180 relay right beside the glow plugs. But instead, it's under the dash. And the solenoid uses the same wires as the relay - I guess I just don't see the issue here. How is an engine bay any safer than under the dash? Is there more or less movement in any one of the places? I know that there's a lot more heat under the hood, which is NEVER good for electronics.

I think what this boils down to is different people's comfort level with modifying what is in place from the factory. Judging by your signature I'm a little surprised at your hesitation towards this. I also had help with this project from an industrial electrician, so maybe that is part of where my confidence is coming from.

No fuse, no protection on your switches terminals.

You say an electrican helped you? I'm an EE and that's just asking for trouble. Put a fuse in, NOW.

Guys, there are fuses. I have said this three times now, this is PARALLEL to the FACTORY system - the system is fused. There is a fuse in the fuse box on top of the battery for the glow plugs, as well as in the fuse panel for the push button, AND the button power is coming from a fused source on the relay harness.

Adding user control does not eliminate the fuses already in place.

Good write-up. I did the same thing 25 yrs ago on a Peugeot with a bad glow plug controller. Back then it worked great for me and now it is working for you.

I'd like to modify my o5 NB too. I am currently using 11v plugs with a 7v supply because I don't trust the original ceramic plugs. If VW does not come up with a better solution, I might try a work around that bypasses the glow plug controller and sends 12v to the plugs.

chrisfiat said:

...you would need an amp meter on the output side to show the current draw of the glow plugs as they functioned (or not).

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True, my test lamp would not show if the rigid harness were unplugged from the glow plug terminals of if any were faulty.
One would need FOUR current flow indicators, one per glow plug, to be certain.
A reduced resistance through one plug could offset an increased resistance through another. The total current would be displayed by one ammeter, but one meter would not display any resistance imbalance that would indicate one partially shorted and one opened glow plug.

NB_TDi said:

No fuse, no protection on your switches terminals.

You say an electrician helped you? I'm an EE and that's just asking for trouble. Put a fuse in, NOW.

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DITTO!!!!!!!! Never install a high power circuit like this without first installing a fuse ...........

You are just asking for a fire that will burn your car to ground if you install something like this without at least a ~50 amp in-line fuse .

Disable this until you have a fuse installed .

An old style glow plug fuse & fuse block would be cheap & perfect for your setup if you can find one in a junk yard . Any VW powered diesel of the IDI era will work fine . A 77 - 92 VW , 78 - 86 Volvo & Audi , all had VW engines . The fuses are cheap and relatively easy to find . A fuse block like the ones used on B4s and A3s will also work .

I would not use a plastic sheathed fuse because in a dead short it can melt causing a dead short that can lead to a fire , I speak from experience .........This is why the VW fuse is just an open piece of metal ,

rotarykid said:

DITTO!!!!!!!! Never install a high power circuit like this without first installing a fuse ...........

You are just asking for a fire that will burn your car to ground if you install something like this without at least a ~50 amp in-line fuse .

Disable this until you have a fuse installed .

An old style glow plug fuse & fuse block would be cheap & perfect for your setup if you can find one in a junk yard . Any VW powered diesel of the IDI era will work fine . A 77 - 92 VW , 78 - 86 Volvo & Audi , all had VW engines . The fuses are cheap and relatively easy to find . A fuse block like the ones used on B4s and A3s will also work .

I would not use a plastic sheathed fuse because in a dead short it can melt causing a dead short that can lead to a fire , I speak from experience .........This is why the VW fuse is just an open piece of metal

Click to expand...

So I'm guessing you missed this?

chaloux said:

Guys, there are fuses. I have said this three times now, this is PARALLEL to the FACTORY system - the system is fused. There is a fuse in the fuse box on top of the battery for the glow plugs, as well as in the fuse panel for the push button, AND the button power is coming from a fused source on the relay harness.

Adding user control does not eliminate the fuses already in place.

Click to expand...

There is nothing to miss, You still have a risk of current flow. Fuse it.

chaloux said:

Judging by your signature I'm a little surprised at your hesitation towards this.

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i have seen TOO many botched home projects this is ter rxeason for my hesitation, look closely at my sig it says master tech NOT master hacker.

when it burns up you will finally understand

Why would I fuse it twice? Is the current going to keep going if one fuse pops?

Seriously - am I missing something here? I keep saying that IT IS FUSED, and you keep telling me to fuse it. The fuse on top of the battery would blow - opening the circuit. What more do you want? A fuse under the dash so I then have to take it all apart if that one happens to blow first? The fuse is right after the battery. If it blows, everything after is NOT live. The solenoid does NOT get a direct feed from the battery. The feed to the solenoid is exactly what the relay got - a fused feed.

These are serious questions because your suggestions make no sense to me. If VW was not happy with the factory setup (using a fuse), would they not have added another one?

I feel like I am really on the defensive here, but I also feel like I'm repeating myself and my explanations, and people aren't giving any explanation in response, or simply aren't acknowledging what I'm telling them. If I didn't trust the fused system that is in place, I would take it out.

And Chris, I am going to politely acknowledge your comment and not respond to it.

Your wiring is not directly connected to the factory wiring, thus not fused.

Wait - did you read my writeup? Did you see what I tapped into? It is directly connected to the factory wiring. The only extra wires (for the switch), are also coming from fused sources.

Where did you get that it's not factory wiring?

Edit: added my wiring diagram from the writeup. This shows that I'm getting everything from what goes to the 180 relay (which is fused). The positive from battery is exactly what the relay gets - which is fused.

That's next to impossible to decipher. But your 'from battery' is that fused? and your 'to fused power' Where is this power?

You still need to cover your leads on your switch.

So you didn't read the guide. I explain it clear as day in the guide. Yes the picture is a little confusing, but paired with an explanation it becomes clear (for example, why and how the "from battery" magically splits into 2). I'd appreciate it if you read the guide before jumping on other people's assumptions.

To answer the question, yes, the "from battery" is fused. It comes off the battery, to the top of the battery where the three or four fuses are, and then continues into the dash. The "to fused power" comes from a fuse that is on the relay harness. There are pictures in the guide showing which one exactly. To be honest, I'm not sure what it's for, but it is fused, with something between 5-20A, probably 10A. I didn't really check it as it was just a safety measure to fuse the switch as well.

Yes I read it, but it's just the same as the picture. I get you are trying to help someone. But you need to approach things the correct way. That picture needs to be a proper schematic.