Electrical Circuits

[lamountain1976]

I am trying to wire the reverse light, a horn (air horn is broke) and the heater/thermostat assembly on the air dryer. I think all of these should go thru fuses to ignition switched power feed. Does that mean wiring them to something that is hot at the fuse box when the ignition is on? Do I just tap into an existing wire? And then everything requires its own ground as well?

[Rob]

I am trying to wire the reverse light, a horn (air horn is broke) and the heater/thermostat assembly on the air dryer. I think all of these should go thru fuses to ignition switched power feed. Does that mean wiring them to something that is hot at the fuse box when the ignition is on? Do I just tap into an existing wire? And then everything requires its own ground as well?

Justin: I don't want to seem forceful or anything negative but I don't hear you saying you have a good handle on what you are trying to accomplish with any of the systems you inquire about. It is great to ask questions and seek others experience but when you go messing with safety issues such as brakes, electrical etc. without a basis of knowledge in the systems you will most likely have problems.

I can only speak for myself but I'm sure others would agree that there would be no enjoyment reading about someone burning their truck to the ground, or rear ending someone at a stoplight quite possibly hurting, (or worse) anyone oblivious to the subject, due to lack of experience on the owners/operators part.

I am a semi professional mechanic/electrician by trade and believe me I do ask a lot of questions also. Like you, I don't want to make mistakes and my position on safety is taken very seriously. A lot of my knowledge is through training, studying, and understanding the information printed in technical manuals. I strongly suggest that you visit your local library, or ebay, and acquire a set of manuals for the truck and systems you are questioning. A very good set that is readily available through ebay, or other sources is Mack factory service manuals: TS-442 series. These manuals go into great detail in both theory, and repair/service proceedures and will help you immensly with your needs.

I ask that you not take anything I have said as an insult as it is not meant that way. Your level of knowlege will increase if you have a basic understanding of what the component is, or does, before you attempt to repair it.

Speaking for all of us here: We only wish you the best of luck with your project.

On several occasions I have obtained much needed advice and guidance from persons here that have experience where I do not. This board is an excellent source of information and help if it relates to Mack trucks.

Good Luck!

Rob

[lamountain1976]

Justin: I don't want to seem forceful or anything negative but I don't hear you saying you have a good handle on what you are trying to accomplish with any of the systems you inquire about. It is great to ask questions and seek others experience but when you go messing with safety issues such as brakes, electrical etc. without a basis of knowledge in the systems you will most likely have problems.

I can only speak for myself but I'm sure others would agree that there would be no enjoyment reading about someone burning their truck to the ground, or rear ending someone at a stoplight quite possibly hurting, (or worse) anyone oblivious to the subject, due to lack of experience on the owners/operators part.

I am a semi professional mechanic/electrician by trade and believe me I do ask a lot of questions also. Like you, I don't want to make mistakes and my position on safety is taken very seriously. A lot of my knowledge is through training, studying, and understanding the information printed in technical manuals. I strongly suggest that you visit your local library, or ebay, and acquire a set of manuals for the truck and systems you are questioning. A very good set that is readily available through ebay, or other sources is Mack factory service manuals: TS-442 series. These manuals go into great detail in both theory, and repair/service proceedures and will help you immensly with your needs.

I ask that you not take anything I have said as an insult as it is not meant that way. Your level of knowlege will increase if you have a basic understanding of what the component is, or does, before you attempt to repair it.

Speaking for all of us here: We only wish you the best of luck with your project.

On several occasions I have obtained much needed advice and guidance from persons here that have experience where I do not. This board is an excellent source of information and help if it relates to Mack trucks.

Good Luck!

Rob

No problem man. I often wish I had a basic understanding of the systems - this is all new territory, but I am confident that I can figure it out between talking to local mechanics and you guys, who have been really helpful. Especially the fellas who take the time to explain the mechanics of how something works, because that helps me conceptualize the system. And I have made some real progress on a truck that has been abused for the last 25 years.

Two months ago, I requested a full set of manuals from the museum, but I still haven't recieved them yet. I will check into the TS-422 series and keep plugging along. Thanks.

[ThaddeusW]

Hmmm you need a new air dryer circuit, reverse light circuit and you also need to fix your air horn. OK. Rob is right you need to be careful but you seem to be a sharp fella so I think you wont take any short cuts.

Ok first off if you can figure out if there was a fuse/circuit breaker for the dryer thats a good start. There should also be a wiring block on the cab because when they make a truck the cab is all pre-wired and so is the chassis. So when they mate the two the chassis harness is connected/plugged to the cabs wiring block. Nowadays its all electronic using a local network to communicate with the different components but not too long ago it was a simple terminal block. Tilt your cab and look for a terminal block toward the front of the cab near the frame rails (there might be more than one). I dont know if they labeled the terminals (they are on my 88 GMC amazingly) but if you do find a fuse/breaker for the air dryer try to trace it to the terminal block. If you find the terminal and you can get power with a good fuse or breaker just run a piece of 14 gauge wire from that terminal block to the air dryer. Ground the other end of the dryer to the frame but make sure its a good ground as a poor ground will render the heater coil ineffective. Use a wire brush to clean around the bolt hole you gonna use for the ground and make your connection.

Let us know if you cant find a fuse or breaker for the air dryer. If not then your gonna have to wire up a new one which wont be so bad.

Ok now your air horn is mounted where? I like em on the roof but some guys like to hide them under the cab or behind the cab or even along the frame rails. Since your going through trees its better to get it off the roof as you don't need a hole in your roof when a branch snagges the horn. If its on the roof the horn usually has a valve with the pull cord and a 1/4 inch hose for air supply from the wet tank and a 1/4 line to the horns(s). If you pull the cord and just hear air hiss out then the horn is no good and needs to be rebuilt/replaced as the diaphragm may be bad or stuck. First check if there is air to the horn valve and then check the horn. If no air to the valve then you need to run a new line. Mostly the same line that supplies air to an air ride seat is tee'd off to the air horn so thats a place to start looking for an air line.

Reverse lights should be wired up at the rear. Again see if you can find a set of wires that are cut back or hanging by the transmission. Didnt you say there was a wire or two by the transmissions rang/splitter valve? Those might be the reverse light wires. I bet they were left disconnected because of a short and they just left them unhooked because they might be on the same fuse as the brake lights. Ok wire tracing time. Best way to see if those two are the reverse lights is to see if you get any juice to them with the key on. You can use a volt meter or a bulb to check for power. next to see if there is a short take a 12 volt bulb and hook the two wires to it. If it glows dim and the reverse lights glow dim then your in luck they work fine. But if it lights up at full brightness then you may not have the reverse lights or have a short. Start following those wires and let us know what you find. We will then see what we can do from there.

Oh and a few tips on good wiring:

Never let wires dangle outside or even inside the cab as they make it easy for them to rub and eventually short out or get ripped off. Use wire ties and tape to secure them to other wires that are already properly ran or any other suitable tie point

And try to make sure if you run a wire through a hole it cant get cut by any sharp edges leading to shorts and possible fire. Keep the wires away from sharp edges. If its near a sharp edge put a good layer of tape around it to toughen it up or smooth out the sharp edge or cover it.

Twisting wires together and throwing some tape around them is the worst way to make a splice. your gonna have fun trying to find the splice that pulled appart when something stop's working. The best splicing method is to solder the splice as this ensures an excellent mechanical and electrical connection. Then get some heat shrink tubing over that splice to ensure its thoroughly insulated and it wont peel off or come off from vibration. Dont use wire nuts that are used in building wiring as they aren't meant for wiring that is subject to vibration ( I have seen this done in auto wiring!).

Crimp connectors are nice but make sure the crimps are done right! They are color coded and certain colors are for certain wire gauges and the crimp tool has corresponding crimp edges that are also color coded. I see people use connectors that are too big and the wire falls out. Don't use a crimp edge thats too small for that color terminal, you can squash it so bad that you shear the wire making a loose/weak connection. I not only crimp them but also let some wire stick out near the terminal and then throw some solder on it to ensure that the connection is thorough.

Let us know your progress or if you need more help!

[lamountain1976]

Hmmm you need a new air dryer circuit, reverse light circuit and you also need to fix your air horn. OK. Rob is right you need to be careful but you seem to be a sharp fella so I think you wont take any short cuts.

Ok first off if you can figure out if there was a fuse/circuit breaker for the dryer thats a good start. There should also be a wiring block on the cab because when they make a truck the cab is all pre-wired and so is the chassis. So when they mate the two the chassis harness is connected/plugged to the cabs wiring block. Nowadays its all electronic using a local network to communicate with the different components but not too long ago it was a simple terminal block. Tilt your cab and look for a terminal block toward the front of the cab near the frame rails (there might be more than one). I dont know if they labeled the terminals (they are on my 88 GMC amazingly) but if you do find a fuse/breaker for the air dryer try to trace it to the terminal block. If you find the terminal and you can get power with a good fuse or breaker just run a piece of 14 gauge wire from that terminal block to the air dryer. Ground the other end of the dryer to the frame but make sure its a good ground as a poor ground will render the heater coil ineffective. Use a wire brush to clean around the bolt hole you gonna use for the ground and make your connection.

Let us know if you cant find a fuse or breaker for the air dryer. If not then your gonna have to wire up a new one which wont be so bad.

Ok now your air horn is mounted where? I like em on the roof but some guys like to hide them under the cab or behind the cab or even along the frame rails. Since your going through trees its better to get it off the roof as you don't need a hole in your roof when a branch snagges the horn. If its on the roof the horn usually has a valve with the pull cord and a 1/4 inch hose for air supply from the wet tank and a 1/4 line to the horns(s). If you pull the cord and just hear air hiss out then the horn is no good and needs to be rebuilt/replaced as the diaphragm may be bad or stuck. First check if there is air to the horn valve and then check the horn. If no air to the valve then you need to run a new line. Mostly the same line that supplies air to an air ride seat is tee'd off to the air horn so thats a place to start looking for an air line.

Reverse lights should be wired up at the rear. Again see if you can find a set of wires that are cut back or hanging by the transmission. Didnt you say there was a wire or two by the transmissions rang/splitter valve? Those might be the reverse light wires. I bet they were left disconnected because of a short and they just left them unhooked because they might be on the same fuse as the brake lights. Ok wire tracing time. Best way to see if those two are the reverse lights is to see if you get any juice to them with the key on. You can use a volt meter or a bulb to check for power. next to see if there is a short take a 12 volt bulb and hook the two wires to it. If it glows dim and the reverse lights glow dim then your in luck they work fine. But if it lights up at full brightness then you may not have the reverse lights or have a short. Start following those wires and let us know what you find. We will then see what we can do from there.

Oh and a few tips on good wiring:

Never let wires dangle outside or even inside the cab as they make it easy for them to rub and eventually short out or get ripped off. Use wire ties and tape to secure them to other wires that are already properly ran or any other suitable tie point

And try to make sure if you run a wire through a hole it cant get cut by any sharp edges leading to shorts and possible fire. Keep the wires away from sharp edges. If its near a sharp edge put a good layer of tape around it to toughen it up or smooth out the sharp edge or cover it.

Twisting wires together and throwing some tape around them is the worst way to make a splice. your gonna have fun trying to find the splice that pulled appart when something stop's working. The best splicing method is to solder the splice as this ensures an excellent mechanical and electrical connection. Then get some heat shrink tubing over that splice to ensure its thoroughly insulated and it wont peel off or come off from vibration. Dont use wire nuts that are used in building wiring as they aren't meant for wiring that is subject to vibration ( I have seen this done in auto wiring!).

Crimp connectors are nice but make sure the crimps are done right! They are color coded and certain colors are for certain wire gauges and the crimp tool has corresponding crimp edges that are also color coded. I see people use connectors that are too big and the wire falls out. Don't use a crimp edge thats too small for that color terminal, you can squash it so bad that you shear the wire making a loose/weak connection. I not only crimp them but also let some wire stick out near the terminal and then throw some solder on it to ensure that the connection is thorough.

Let us know your progress or if you need more help!

Thanks for the encouragement Thad. I have been copying and pasting your responses into word docs, which have been real good to have on hand while working on the truck.

WRT the reverse light. I found the switch in the top of the transmission. Cleaned it up, threaded two screws into it and ran one line back to the light and one forward to the fuse box in the cab. This is the only fuse box/terminal block I have found. All the wires seem to just run straight along the frame rails and then up into the forward part of the cab thru the floor. There is no labelled fuse for it.

WRT the air dryer. I ran a wire from it up to the fuse box as well. There is also no labelled fuse for it, and I still have to ground it.

WRT the horn. The air horn is mounted on the roof, but the cable has been cut and the actuator valve is hard to get at, up in the overhead console. A good future project. So for right now, I was just going to wire an electric horn. There is a horn relay and a fuse for the horn in the fuse box.

So I have a test light and a pretty good connector kit for running 14 to 16 gage wire. I have run the above wires, but not connected them to power yet because I want to do this right and I don't quite understand automotive electrical.

Here is what confuses me. If this is about open and closed circuits, and it is important to run these wires thru a fuse to ignition switched power, what exactly is the wire going to? An empty port on the fuse box? Because there are some empty ports (e.g. heated mirrors, air horn, etc.), or I gues I could just create my own fuse? So when the key is on, and I pull a fuse, one side will light the test light, the other will not. So the fuse is completing the circuit, protecting the hardware. Do I just lag into a wire that is live when the key is on? It probably seems clear to most of you, but I can't imagine the right way to get power to come thru the fuse and then out to the device being powered. It seems like a bad idea to start tapping into other wires...

[ThaddeusW]

Ok,

Now some circuits are always live in the truck like lights, cigar lighter and whatever else turns on without the key. Now there is a solenoid somewhere that hooks to the run position of the key switch that turns on the rest of the equipment like the radio, fuel cutoff (to turn engine off with the key) heater and air dryer heater among other things.

I don't know what your fuse block looks like so bear with me. If you see an open fuse slot like the one for heated mirrors, get your tester out and see if it has power with the ignition key on. Only one side should be live and the other side is where the mirror switch wire would have hooked. Now instead of the mirror switch hook one of your wires to it and put a 10 amp fuse in there. Do the same with another unused fuse slot.

If you only have one extrea fuse to hook up to then your going to have to split that fuse to the two circuits and then fuse each circuit seperatly. Now before you get conFUSEd let me break it down a little. Each of those two circuits (Reverse and air dryer) need their own fuse for circuit protection. But you have only one AUX fuse to spare. So you figure out how much current each circuit will draw and then get an inline fuse holder for each line and plug in the properly rated fuse for that circuit. Then join the two wires together and then run them to a larger fuse that has the ability to supply both circuits. Now lets do a little basic math to see how much juice the circuits can use.

If your air dryer heater is 90 watts (which is the most for a 12v heater on an AD2) we need the amps so we simply divide 90 by 12 and get 7.5 amps. Fuses typically come in 10-15-20-25-30 amps so 10 amps is the best rating. Now the two reverse lights will also draw very little so fuse them with a 10 amp as well. Now you have two separate 10 amp circuits and one fuse to spare so just plug a 20 amp into the aux and then hook the two circuits to that. Here is a simple diagram:

Here is an example of an inline fuse holder for the blade fuses. And here is one for the 1.25x.25 inch round fuses. Both can be had at any auto parts store.

I hope this helps, if not keep asking questions, thats what we are here for

[sdthoren]

Justin,

I was researching starters/alternators & thought of your post. Here's a couple of websites that may be of general help and good reference:

http://www.prestolite.com/pgs_training/training_0.php - Prestolite (Leece Neville) electrical manual

http://www.hss.energy.gov/NuclearSafety/te...d/standard.html - There are a bunch of manuals here. Some of the electrical fundamental handbooks deal with DC circuits, but mainly AC circuits.

Hope this helps,

Scott

[lamountain1976]

Justin,

I was researching starters/alternators & thought of your post. Here's a couple of websites that may be of general help and good reference:

http://www.prestolite.com/pgs_training/training_0.php - Prestolite (Leece Neville) electrical manual

http://www.hss.energy.gov/NuclearSafety/te...d/standard.html - There are a bunch of manuals here. Some of the electrical fundamental handbooks deal with DC circuits, but mainly AC circuits.

Hope this helps,

Scott

Thanks a lot man. The manuals are key.

[lamountain1976]

Thanks a lot man. The manuals are key.

Its all sorted out. Thanks a lot fellas. Say, if one wanted to power the block heater using batteries, how many would it take and could you rig up the cables such that the truck would recharge the batteries? Or maybe a solar charger, off a fence?

[ThaddeusW]

Its all sorted out. Thanks a lot fellas. Say, if one wanted to power the block heater using batteries, how many would it take and could you rig up the cables such that the truck would recharge the batteries? Or maybe a solar charger, off a fence?

Well the block heaters are usually 120V AC (240V AC in other places). This presents the problem of conversion which gets too expensive and impracticle. If one could find a 12 volt heater then thats a different story. But a 1000 watt 12 volt heater would have to draw 83 amps and a 1500 watt would draw 125 amps. Thats allot of current and you would need a battery bank with at least 150-200 amp hours capacity to warm that block up. Maybe an air intake heater would do better?

[lamountain1976]

Well the block heaters are usually 120V AC (240V AC in other places). This presents the problem of conversion which gets too expensive and impracticle. If one could find a 12 volt heater then thats a different story. But a 1000 watt 12 volt heater would have to draw 83 amps and a 1500 watt would draw 125 amps. Thats allot of current and you would need a battery bank with at least 150-200 amp hours capacity to warm that block up. Maybe an air intake heater would do better?

Okay, just a thought. Also, the air ride seat is not connected. Can I just tee into an existing line to get pressure to the controller?

[ThaddeusW]

Okay, just a thought. Also, the air ride seat is not connected. Can I just tee into an existing line to get pressure to the controller?

Hmmm the air line that runs to the air ride seat is also the same line that usually runs up to the horn but it could be different. As long as you plumb the line from the wet tank your good to go.

[WHITE9064TD]

Hmmm the air line that runs to the air ride seat is also the same line that usually runs up to the horn but it could be different. As long as you plumb the line from the wet tank your good to go.

While you are waiting for your manual to arrive I strongly urge you to either go to the library or bookstore and get a book on basic automotive/truck electrical systems. You really need a basic knowledge of electricity and how to use multiy meters, it will save you time and possible a big repair. I have been down that road you are on, sorry to be a wet blanket but I can see what is coming: been there and done that.