Glow Plug Relay Indicator LED
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Senior User
Joined: Oct 2004
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From: King George, Virginia
Glow Plug Relay Indicator LED
Just thought I would share my latest little invention for my truck. Well, not really an invention but just a cool indicator. I am always wondering if the GPR is working properly and with my truck, I cannot really hear it engage in the mornings. I installed a simple 12vdc circuit with a green LED to light during glow plug operation.
<O
I was planning to use a Field Effect Transistor as a current limiting device for the LED but while shopping at Radio Shack, I discovered they had already figured it out for me. They sell a 12VDC LED already in a socket ready to install (limiting resister in the socket). I connected a small tap wire off the output of the GPR and routed this in the truck and put an inline fuse in the circuit. Ground the other lead and you have it, a LED that lights when the GPR energizes. I drilled a small hole in the lower part of the dash to mount the LED.
<O
With as often as we have GPR post, this is a nice indicator to let you know everything is operating properly. Well, not that the glow plugs are working but does let you know that the relay has fired and the glow plugs have 12vdc. Figured others might like this as well.
<O
I was planning to use a Field Effect Transistor as a current limiting device for the LED but while shopping at Radio Shack, I discovered they had already figured it out for me. They sell a 12VDC LED already in a socket ready to install (limiting resister in the socket). I connected a small tap wire off the output of the GPR and routed this in the truck and put an inline fuse in the circuit. Ground the other lead and you have it, a LED that lights when the GPR energizes. I drilled a small hole in the lower part of the dash to mount the LED. <O
With as often as we have GPR post, this is a nice indicator to let you know everything is operating properly. Well, not that the glow plugs are working but does let you know that the relay has fired and the glow plugs have 12vdc. Figured others might like this as well.
Hotshot
Joined: Nov 2006
Posts: 11,286
Likes: 263
From: North of Greenville
Cool beans, Riceman. I tried to give you some rep, but I have to spread it around.
Since I'm pretty dangerous with electricty (and still have a stupid propensity to change recepticles while they're hot), what would help me is if you could sort of sketch out the circuit, tell me which wires you connected to, and share the RS part number for the LED bulb & base. There might even be a few others around here who need as much help as I do with this kind of thing .
Since I'm pretty dangerous with electricty (and still have a stupid propensity to change recepticles while they're hot), what would help me is if you could sort of sketch out the circuit, tell me which wires you connected to, and share the RS part number for the LED bulb & base. There might even be a few others around here who need as much help as I do with this kind of thing .
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Joined: Oct 2004
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From: King George, Virginia
Radio shack has two sizes, take your pick. I picked the larger of the two. The colors available are green, red, and orange. It will say for a 12VDC system. I threw away the package so I do not have the exact part number but it is very easy to find at R/S. Just depends on how big of a hole you are willing to drill in the dash.
Under the hood, find your glow plug relay. The output side has the large lug with the two yellow wires. Takes a 1/2 inch socket. I crimped on a connector that would fit this size lug to a small wire and ran this into the truck. Under the brake reservoir is a place you can get the wire in the cab. I put a small fuse inline with this wire.
The LED indicator only has two wires off it. Connect the wire from the GPR to the red wire on the LED and connect the black wire to ground. I used a mounting bolt under the dash for the ground.
By the way, this morning it worked like a champ. Lights up and stays lit a minute or so after the truck is running. Just like the book says. This is a really simple mod and the LED cost less than 2.00. With the fuse holder my total was still less than 5.00.
Under the hood, find your glow plug relay. The output side has the large lug with the two yellow wires. Takes a 1/2 inch socket. I crimped on a connector that would fit this size lug to a small wire and ran this into the truck. Under the brake reservoir is a place you can get the wire in the cab. I put a small fuse inline with this wire.
The LED indicator only has two wires off it. Connect the wire from the GPR to the red wire on the LED and connect the black wire to ground. I used a mounting bolt under the dash for the ground.
By the way, this morning it worked like a champ. Lights up and stays lit a minute or so after the truck is running. Just like the book says. This is a really simple mod and the LED cost less than 2.00. With the fuse holder my total was still less than 5.00.
Lead Driver
Joined: Dec 2003
Posts: 5,250
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I did that for my dad in his truck. Since its a 1990, the gp controller had gone out, so I put in a manual push button switch and a little LED like you did. It was a simple project, but works like a charm. I have thought about doing it in mine as well, but want on that is more of a gauge style or combo. I am still looking, but its one of those in betweens like Texas said.
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Originally Posted by badger2196
Now why didn't Ford think of that! 
One question before I go out and buy the parts - how many amps is that inline fuse you put in?
One question before I go out and buy the parts - how many amps is that inline fuse you put in?
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Senior User
Joined: Oct 2004
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From: King George, Virginia
Concur, 1/2 amp fuse should be fine. A 1/4 amp fuse will work as well. LEDs draw very little current, 6 to 8ma range.
Today I cleaned up the install a little by putting an o-ring between the LED face and the dash. Just made things look better. Little 1/4 inch id o-ring. When I drilled the hole, I should have stopped at 1/4 inch, it was a little tight so I went one size larger and that ended up just a touch too large. The o-ring cleaned that up. I should have used the 1/4 inch drill bit and cleaned it up with a little round file.
Today I cleaned up the install a little by putting an o-ring between the LED face and the dash. Just made things look better. Little 1/4 inch id o-ring. When I drilled the hole, I should have stopped at 1/4 inch, it was a little tight so I went one size larger and that ended up just a touch too large. The o-ring cleaned that up. I should have used the 1/4 inch drill bit and cleaned it up with a little round file.
Hotshot
Joined: Nov 2006
Posts: 11,286
Likes: 263
From: North of Greenville
I just picked up my parts last night at RS. Hopefully, I may be able to install them this weekend. I went ahead and got the extra heavy-duty fuse holder, so my totla cost last night was $8.
One thing I wanted to do differently was to use the orange LED, which was a little bit larger, but they were out of stock, so I got the little green one.
One thing I wanted to do differently was to use the orange LED, which was a little bit larger, but they were out of stock, so I got the little green one.