Power for Demco Wireless Coachlink June 18, 2022, 08:13:44 pm The “check entry step” light is right next to my Demco brake controller. Power is supplied to the step light when the key is in the on position. Could I tap into the light wiring to provide power to the brake controller? Right now it plugs into a 12V outlet but I prefer it be hardwired. Actually, it’s not really a controller; just a remote warning system to tell me the toad brakes are being applied.Wireless Coachlink for Braking Systems | Demco Products
Re: Power for Brake Controller Reply #1 – June 19, 2022, 11:40:32 am Assuming I can tap off of the entry step light, how can I tell which wire is negative and which is positive (electrical dummy here)? One wire is red, the other white.
Re: Power for Brake Controller Reply #2 – June 19, 2022, 12:33:25 pm "...how can I tell which wire is negative and which is positive..."Normally it's a safe bet to say the red wire is positive!You need to acquire a good Multi-meter and learn how to use it. They can be had on the cheap but mid-price will get you a better instrument. Place Multi-meter's red lead to red wire and it's black lead to the white wire (or any convenient chassis ground point) and you'll know which one is 'hot'.
Re: Power for Brake Controller Reply #3 – June 19, 2022, 02:00:05 pm In RV 12 V wiring, white is usually negative/ground, and any other color (even black) is usually positive. But I have heard of exceptions (new guy at the factory, maybe?), so never take that for granted. I strongly second the suggestion to get a multimeter. They're good for all kinds of things around the house--you'll never regret having one. For a beginner's guide to using a multimeter, see this article on my website.If you're on a budget, I suggest getting the least expensive digital meter that has autoranging. That feature means the controls will be simpler and less confusing. For example, avoid meter like this one, with dozens of settings:It'll work, but it's hard to figure out which setting to use, and easy to get the wrong one. An autoranging meter such as this under-$25 model is easier to work with:If you want the best, you can't beat a Fluke, such as this $83 Fluke 106 model.Yes, it's more expensive, but it's guaranteed accurate, it'll last a lifetime... and it's even simpler to operate than the previous one. 1 Likes As an Amazon Associate Lazy Daze Owners' Group earns from qualifying purchases.
Re: Power for Brake Controller Reply #4 – June 19, 2022, 02:30:49 pm Thanks, Steve and Andy! So no problem with tapping into that circuit then? Would I need to add a fuse for the Demco wiring? If so, how do I determine what size fuse?
Re: Power for Brake Controller Reply #5 – June 19, 2022, 05:16:01 pm "Would I need to add a fuse for the Demco wiring?"Maybe. Simplified answer: if the wires powering the Demco remote warning system are a smaller gauge than the wires leading to the “check entry step” light, then you should add a fuse. You should always use a fuse when going from larger to smaller wire, in order to protect the smaller wire. But there's a good chance you won't be able to see the wire gauge printed on the “check entry step” light's wires, since the accessible section is so short. In that case you'll have to look at the physical sizes of the wires you're comparing. That's not precise, since insulation thickness can vary, but it'll get you close."If so, how do I determine what size fuse?"I could refer you to ampacity tables, but it can be complicated to figure out what applies to your situation. So again I'll give a simplified answer: assuming you need a fuse, you'd probably be OK with one that is one size smaller than whatever is protecting the “check entry step” light. For example, if that's 20 amps, you'd go down to 15 A for the Demco indicator. 1 Likes
Re: Power for Brake Controller Reply #6 – June 19, 2022, 06:48:15 pm Thanks, Andy. I just went out and was able to read the size on the two insulations. The step light is 16 AWG and the Demco is 22 so I will add a 15 amp inline fuse if I proceed with it. BTW, I did buy an autoranging DMM based on a previous discussion we had, and looking at your website. I just haven’t used it yet! 1 Likes
Re: Power for Brake Controller Reply #7 – June 19, 2022, 07:33:48 pm Greg,As Andy said, you size the fuse to protect the smallest wire. The various ampacity tables I looked at put the maximum current a 22 gauge wire can carry at around 7 amps. Nobody in there right mind would ever try to run 7 amps through a 22 gauge wire and is waaaaay more current then the Demco indicator light will ever draw. You could easily protect the Demco 22 gauge wire and light with a 1 amp fuse. After all… this is just an indicator light, not the brake controller you’re fusing.- John 3 Likes
Re: Power for Brake Controller Reply #8 – June 19, 2022, 08:11:27 pm John, earlier I had to disassemble the 12V cigarette plug to see what size the wires were. Your comment spurred my memory that there was a fuse inside the plug so I went back out to see the rating. Yes, it’s a 1 amp so you hit the nail on the head! Thanks!
Re: Power for Brake Controller Reply #9 – June 20, 2022, 02:14:20 pm John is correct: you can use a much smaller fuse than 15 A. I should have said that I was giving general advice based on a worst-case scenario, and not knowing the smaller wire's capacity. But since your Demco's 12 V plug's fuse is 1 A, that tells you what you need to know. :-)
Re: Power for Demco Wireless Coachlink Reply #10 – June 20, 2022, 02:21:24 pm Thanks, Andy. BTW, I changed the subject of this thread to better reflect what we're talking about, and added a link to the product to my original post.
Re: Power for Demco Wireless Coachlink Reply #11 – June 23, 2022, 11:56:33 am Quote from: JohnR - June 19, 2022, 07:33:48 pmAs Andy said, you size the fuse to protect the smallest wire. The various ampacity tables I looked at put the maximum current a 22 gauge wire can carry at around 7 amps. Nobody in there right mind would ever try to run 7 amps through a 22 gauge wire and is waaaaay more current then the Demco indicator light will ever draw. You could easily protect the Demco 22 gauge wire and light with a 1 amp fuse. After all… this is just an indicator light, not the brake controller you’re fusing.Thanks, John. So I just noted in a photo on another thread that the fuse for the step light, which is behind the easily removable dash section under the steering wheel, is rated for 3 amps. Can I use that same fuse to also protect the 22 AWG wires for the Demco? Or do you advise installing a separate 1 amp inline fuse. Am I correct in assuming that only the “hot” wire be fuse protected?
Re: Power for Demco Wireless Coachlink Reply #12 – June 23, 2022, 01:31:58 pm Quote from: HiLola - June 23, 2022, 11:56:33 amThanks, John. So I just noted in a photo on another thread that the fuse for the step light, which is behind the easily removable dash section under the steering wheel, is rated for 3 amps. Can I use that same fuse to also protect the 22 AWG wires for the Demco? Or do you advise installing a separate 1 amp inline fuse. Am I correct in assuming that only the “hot” wire be fuse protected?Hi Greg,Yes you only need to fuse the hot (+) wire. Tapping into the step light circuit is what I would do and not worry about putting in a separate fuse. The 3 amp step light fuse is more than adequate to protect both the step light wire and the 22 gauge Demco wire. Pull the 3 amp fuse out of its holder and use your multimeter to figure which side of the fuse holder is hot. Tap into the non-hot side of the fuse holder with your 22 gauge Demco wire. That way you are protecting both the step light wire and the Demco wire. Also, by pulling the 3 amp fuse first, you don’t need to turn any other power source off.- John 2 Likes
Re: Power for Demco Wireless Coachlink Reply #13 – August 11, 2022, 03:02:31 pm Thanks for everyone's input! Finally finished this up today. I tapped into the hot side of the "Step Light" circuit. I thought that wiring was 16 gauge but closer examination revealed it's 12 gauge. The Demco unit is 22 gauge. This solves one of the issues I had on our last trip of the 12V cigarette plug providing "flakey" power.
Re: Power for Demco Wireless Coachlink Reply #14 – August 11, 2022, 03:11:03 pm Whoops, I just reread JohnR's reply #12. He said to tap into the non-hot side of the step light wiring; I mis-read it and tapped into the hot side (before the fuse). What are the possible consequences of that?
Re: Power for Demco Wireless Coachlink Reply #15 – August 11, 2022, 08:42:57 pm Hi Greg; Virtually none. Should work fine. Any problem with 22 gauge wire (receiver for Demco) will go unnoticed by the 12 ga. wire. RonB
Re: Power for Demco Wireless Coachlink Reply #16 – August 15, 2022, 12:40:08 pm Quote from: RonB - August 11, 2022, 08:42:57 pmHi Greg; Virtually none. Should work fine. Any problem with 22 gauge wire (receiver for Demco) will go unnoticed by the 12 ga. wire. RonBThanks for your input, Ron. I decided to re-do the power. I removed the splice from the hot side and put in a new splice on the non-hot side of the 3-amp fuse. I was a little worried about the Demco unit getting fried if something glitched. Everything seems to be working fine. 1 Likes
Re: Power for Demco Wireless Coachlink Reply #17 – August 16, 2022, 05:59:00 pm Who labeled the wires? That's a kind thing to do when someone else is looking at it. And next year when you have forgotten, you are that 'someone else'
Re: Power for Demco Wireless Coachlink Reply #18 – August 16, 2022, 10:25:38 pm Joel, those are factory labels.