Attention: TDR Forum Junkies 
rbattelle
TDR MEMBER
When built my low pressure fuel system one of the features I included was a pair of LEDs connected to the grid heaters so that I can watch them in action. This also offers a nice way to be sure the relays that activate the grids are functioning (the relays are the most likely part of the grid heater system to malfunction, in my opinion). It recently occurred to me that others might be interested in a little “how to” with regard to this simple mod. So here goes.
You will need the following items:
1. Approximately 30ft. of insulated wire. Current will be very low, so anything 20ga. or larger will be fine. I suggest buying 20ft. Of red, and 10 ft. of black.
2. Your favorite brand of 3/8" ring terminal sized to fit the wire you bought. This can be had at almost any auto or home improvement store, and comes in many varieties.
3. A soldering iron and solder.
4. Basic wiring tools (cutters, strippers).
5. (2) LEDs.
6. (2) resistors (we’ll talk about what kind shortly).
7. Some type of wire sealant, be it shrink tube, electrical tape, liquid electrical tape, silicone tape, or whatever.
8. A heat gun if you plan to use any shrink tubing.
Then the procedure to install your LEDs is as follows:
1. Select your LEDs.
The LEDs you choose will determine what kind of resistors you need; that’s why we choose the LEDs first. We’re going to have to do a little math here, but I promise it’s very easy; math-phobics have no fear. LEDs are rated by two values: current and voltage. Although there are 12v LEDs which could be connected to the heaters directly without resistors, they’re likely to be too bright or too large for use inside the cab. Instead, we choose a smaller LED with a reasonable light output. The formula to figure out the required resistor, then, is:
Resistance = (12 - LED_Volts)/LED_current
In my case, I purchased 2 red LEDs from Newark Electronics , part number 559-5101-007 (data sheet) . These fit in a 1/4" hole and, in my opinion, are perfectly sized in terms of light output and physical dimensions. They run $2. 25 each. The specifications for these LEDs indicate they operate on a current of 20 mA (0. 020 amp) and a voltage of 2. 1v. Then we simply plug that into the formula for resistance:
Resistance = (12 - 2. 1)/(0. 020) = 495 ohm
So we need a resistor with 495 ohm in order to power this LED from a 12v source. Of course, there’s not really any such thing as a 495 ohm resistor in common availability, so we simply need to pick one that’s close, but not lower than 495 ohm. I ended up using 520 ohm because that’s what the local electronics shop had in the power that I needed.
There’s one other thing we need to calculate: the power consumption of the LEDs. Resistors are sized based on the wattage they can dissipate, so we need to be sure we get a resistor with enough power dissipation to not burn up when it’s connected. Power is calculated by the following formula:
Power =(12- LED_volts) * LED_current
In my case, this works out to:
Power = (12 - 2. 1) * 0. 020 = 0. 2 watt
So I needed a minimum 1/4 watt resistor. As I recall (it’s been awhile), I bought a 1-watt resistor just to be safe. It’s okay to get one larger than you need, just don’t get one smaller than you need.
That’s all the math we need! At this point in the example we need 2 495 Ohm, 1/4-watt (or more) resistors. As I mentioned, I used 2 1-watt 520 Ohm resistors (520 Ohm was the closest standard resistor value to 495).
2. Solder your resistors to your LEDS.
Take one side of each resistor and solder it to the end of the positive lead coming out of each LED. At this point in the process, then, you should have 2 LEDs, each with it’s own resistor soldered onto the positive (red) lead.
3. Cut your wiring.
At this point you need to decide where in the cab to mount your LEDs. I used the A-pillar. The wires are going to attach to the heater grid relays which are near the passenger-side battery. In my case, I used around 8ft of wire to get from the pillar to the grid relays. I had plenty of extra. Remember: it’s easier to shorten a wire than it is to lengthen it later on, so don’t be afraid to give yourself plenty of flexibility. You’ll need at least 2 wires (possibly 4, depending on where you want to put your ground... see step 5).
4. Solder your wiring to your LEDs.
Solder your positive wires to the free end of the resistors you soldered to the LED leads back in step 2. At this point you should have 2 LEDs, each with a resistor soldered inline between the LED lead and the long wire you’ll be running out to the engine compartment. Protect the resistors at this point! I used some liquid electrical tape to “paint” over any exposed metal of the resistor leads. Shrink tube, electrical tape, or silicone tape would’ve worked just as well.
5. Ground the LEDs.
The negative (black) lead on the LEDs needs to connect to a ground. THE NEGATIVE LEADS DON’T NEED RESISTORS ON THEM! Use any convenient ground source. Most of the vehicle body is grounded, so you may choose to remove a bolt and run your grounds over to it with ring terminals on the ends. Or, if you’re really crazy, you can run the grounds all the way out to the engine compartment and connect to one of the battery negatives.
6. Put your ring terminals on the ends of the positive leads.
Attach the ring terminals you bought to the ends of the positive leads. Run the leads out into the engine compartment, across to the passenger side battery, and down to where the heater grid relays are. The heater grid relays are located directly in front of the passenger side battery.
7. Connect the ring terminals to the grid-side (engine-side) posts on each of the relays.
The heater grid relays are located directly in front of the passenger side battery. There are 2 of them, and they each have 2 posts. On one post is a direct connection to the battery; that post is on the side closest to the battery. On the other post, closest to the engine, is a wire that runs across the front of the engine to the grid heaters. I’ve attached a picture of the grid heater relays from the service manual. Each of the 4 posts has a little rubber flap on it to help keep out water. Lift up the rubber flap on the heater-grid side of each relay one-at-a-time and remove the nut. Slip your ring terminal onto the post, and reinstall the nut.
8. Be sure your wiring is tied up out of the way of any rotating components, and you’re done!
That’s all there is to it! I know it’s a lot of reading, but this job is very simple and very low-risk. Probably the biggest risk is that you pick the wrong size resistor and end up burning out an LED. It’s impossible to ruin your grid heaters with this mod, so don’t worry about it.
You may notice I didn’t comment on using the heat gun. That’s because you’ll only need it if you use shrink tubing for any part of it. I figure if you know what shrink tubing is, you probably know how to use it.
I’ve also attached a very simple circuit diagram. Please excuse the non-standard symbols... you get the point.
Also note that this procedure is not specific to the grid heaters: the calculations are valid for any 12v system. For example, I could use the exact same LEDs and resistor values to connect to the fuel heater, and they would light up any time the fuel heater came on (in fact, I plan to do exactly that, eventually). The only "key" is to be sure to tie into the circuit in parallel (if you wire in series you'll blow your LEDs the first time the circuit comes on).
I'd post some pictures to make this even easier, but my digital camera is broken and I probably have to wait for Christmas to get a new one.
-Ryan
You will need the following items:
1. Approximately 30ft. of insulated wire. Current will be very low, so anything 20ga. or larger will be fine. I suggest buying 20ft. Of red, and 10 ft. of black.
2. Your favorite brand of 3/8" ring terminal sized to fit the wire you bought. This can be had at almost any auto or home improvement store, and comes in many varieties.
3. A soldering iron and solder.
4. Basic wiring tools (cutters, strippers).
5. (2) LEDs.
6. (2) resistors (we’ll talk about what kind shortly).
7. Some type of wire sealant, be it shrink tube, electrical tape, liquid electrical tape, silicone tape, or whatever.
8. A heat gun if you plan to use any shrink tubing.
Then the procedure to install your LEDs is as follows:
1. Select your LEDs.
The LEDs you choose will determine what kind of resistors you need; that’s why we choose the LEDs first. We’re going to have to do a little math here, but I promise it’s very easy; math-phobics have no fear. LEDs are rated by two values: current and voltage. Although there are 12v LEDs which could be connected to the heaters directly without resistors, they’re likely to be too bright or too large for use inside the cab. Instead, we choose a smaller LED with a reasonable light output. The formula to figure out the required resistor, then, is:
Resistance = (12 - LED_Volts)/LED_current
In my case, I purchased 2 red LEDs from Newark Electronics , part number 559-5101-007 (data sheet) . These fit in a 1/4" hole and, in my opinion, are perfectly sized in terms of light output and physical dimensions. They run $2. 25 each. The specifications for these LEDs indicate they operate on a current of 20 mA (0. 020 amp) and a voltage of 2. 1v. Then we simply plug that into the formula for resistance:
Resistance = (12 - 2. 1)/(0. 020) = 495 ohm
So we need a resistor with 495 ohm in order to power this LED from a 12v source. Of course, there’s not really any such thing as a 495 ohm resistor in common availability, so we simply need to pick one that’s close, but not lower than 495 ohm. I ended up using 520 ohm because that’s what the local electronics shop had in the power that I needed.
There’s one other thing we need to calculate: the power consumption of the LEDs. Resistors are sized based on the wattage they can dissipate, so we need to be sure we get a resistor with enough power dissipation to not burn up when it’s connected. Power is calculated by the following formula:
Power =(12- LED_volts) * LED_current
In my case, this works out to:
Power = (12 - 2. 1) * 0. 020 = 0. 2 watt
So I needed a minimum 1/4 watt resistor. As I recall (it’s been awhile), I bought a 1-watt resistor just to be safe. It’s okay to get one larger than you need, just don’t get one smaller than you need.
That’s all the math we need! At this point in the example we need 2 495 Ohm, 1/4-watt (or more) resistors. As I mentioned, I used 2 1-watt 520 Ohm resistors (520 Ohm was the closest standard resistor value to 495).
2. Solder your resistors to your LEDS.
Take one side of each resistor and solder it to the end of the positive lead coming out of each LED. At this point in the process, then, you should have 2 LEDs, each with it’s own resistor soldered onto the positive (red) lead.
3. Cut your wiring.
At this point you need to decide where in the cab to mount your LEDs. I used the A-pillar. The wires are going to attach to the heater grid relays which are near the passenger-side battery. In my case, I used around 8ft of wire to get from the pillar to the grid relays. I had plenty of extra. Remember: it’s easier to shorten a wire than it is to lengthen it later on, so don’t be afraid to give yourself plenty of flexibility. You’ll need at least 2 wires (possibly 4, depending on where you want to put your ground... see step 5).
4. Solder your wiring to your LEDs.
Solder your positive wires to the free end of the resistors you soldered to the LED leads back in step 2. At this point you should have 2 LEDs, each with a resistor soldered inline between the LED lead and the long wire you’ll be running out to the engine compartment. Protect the resistors at this point! I used some liquid electrical tape to “paint” over any exposed metal of the resistor leads. Shrink tube, electrical tape, or silicone tape would’ve worked just as well.
5. Ground the LEDs.
The negative (black) lead on the LEDs needs to connect to a ground. THE NEGATIVE LEADS DON’T NEED RESISTORS ON THEM! Use any convenient ground source. Most of the vehicle body is grounded, so you may choose to remove a bolt and run your grounds over to it with ring terminals on the ends. Or, if you’re really crazy, you can run the grounds all the way out to the engine compartment and connect to one of the battery negatives.
6. Put your ring terminals on the ends of the positive leads.
Attach the ring terminals you bought to the ends of the positive leads. Run the leads out into the engine compartment, across to the passenger side battery, and down to where the heater grid relays are. The heater grid relays are located directly in front of the passenger side battery.
7. Connect the ring terminals to the grid-side (engine-side) posts on each of the relays.
The heater grid relays are located directly in front of the passenger side battery. There are 2 of them, and they each have 2 posts. On one post is a direct connection to the battery; that post is on the side closest to the battery. On the other post, closest to the engine, is a wire that runs across the front of the engine to the grid heaters. I’ve attached a picture of the grid heater relays from the service manual. Each of the 4 posts has a little rubber flap on it to help keep out water. Lift up the rubber flap on the heater-grid side of each relay one-at-a-time and remove the nut. Slip your ring terminal onto the post, and reinstall the nut.
8. Be sure your wiring is tied up out of the way of any rotating components, and you’re done!
That’s all there is to it! I know it’s a lot of reading, but this job is very simple and very low-risk. Probably the biggest risk is that you pick the wrong size resistor and end up burning out an LED. It’s impossible to ruin your grid heaters with this mod, so don’t worry about it.
You may notice I didn’t comment on using the heat gun. That’s because you’ll only need it if you use shrink tubing for any part of it. I figure if you know what shrink tubing is, you probably know how to use it.
I’ve also attached a very simple circuit diagram. Please excuse the non-standard symbols... you get the point.
Also note that this procedure is not specific to the grid heaters: the calculations are valid for any 12v system. For example, I could use the exact same LEDs and resistor values to connect to the fuel heater, and they would light up any time the fuel heater came on (in fact, I plan to do exactly that, eventually). The only "key" is to be sure to tie into the circuit in parallel (if you wire in series you'll blow your LEDs the first time the circuit comes on).
I'd post some pictures to make this even easier, but my digital camera is broken and I probably have to wait for Christmas to get a new one.
-Ryan
Your like a good friend of mine that I used to race with. He was helping me do springs on the front of my truck and proceeded to take my factory air tube apart and gut it cause he thought it looked restrictive. :--)
