Trailer brake issues

[James McClure]

Morning everyone. Problem, trailer brakes pulsate (apply then release) when 4 way flashers operating. Brakes, electronic brake controller and all lights function as they are designed. I know what the cause is (4 way flashers use the brake light circut, not the signal light circuts) I thought of several different ways to beat this, but all of them are rather cumbersom or draw to much current. I thought of using a switch to stop the backfeed into the controller to kill brake imput, but then I wouldn't have trailer brakes when the 4 ways were on. I thought of using a relay but the added load of the relay coil would strain an already loaded circut. My last idea was to use a diode to stop the backfeed into the brake light circut and still have the trailer brakes operate normally. Diode has to be able to handle at least 10 amps, 15 or 20 would be better. Question, does anyone know where I might locate such a diode? Radio Shack isn't any help and the trailer place doesen't even understand the problem. Many thanks, Jim

[TexasJeff]

Hey Jim,

I just installed the 7 way plug on my truck this summer, i have never heard of this problem. Thinking back I don't think I have tried to use the 4 way flasher while pulling the trailer. I might have to check this out next time I have the trailer hooked up. I had some other issues, but I think it was internal to the fuse block, had the hot lead hooked close to the radio hot lead. Everytime I stepped on the brake the radio went on and off. Moved the hot lead for the trailer brakes and problem did not happen any more. I will let you know if I have the same problem with the 4 ways.

[454HO]

Try this pulse preventer

[77gmcjoe]

I've had quite a bit of experience with trailer brake and wiring issues (from my years of experience as a carny, LOL), and they're really not anything too complicated. I've never heard of anyone needing to do any of the elaborate fixes that you've mentioned. You've probably just got some kind of a simple short, or what I've found to be the problem with trailer lights about 99% of the time, a bad ground.

[James McClure]

77: After 33 years spinning wrenches for Chev & Gmc on light trucks and going through General Motors S.E.T. (specialized electronics training) I pretty much know electrical work. No insult intended. Re-read my post. Problem is built into the truck at the factory believe it or not. Signal lights use 2 different circuts, brake lights use 1 circut. Here's where the problem is, both circuts use the same element in the lamp. The signal light switch cuts off power to the brake light circut on the side your signaling to but allows power to go to the opposite side. With the 4 ways on the switch doesen't do this and power backfeeds up the brake circut. That's why the 4 ways lock up when you apply the brake. You can see this backfeed with a test light at the brake light switch. Turn 4 ways on and back probe white wire and it's flashing. Newer vehicles don't exhibit this because the two systems (brake light and signal light circuts) are segregated from each other and use a seperate bulb. The reason for this is A.B.S.. A.B.S. needs a dedicated and uninteruptable brake apply feed. A.B.S. equiped vehicles won't lock the 4 ways up when you hit the brake. It's complicated here to try and explain this. I've been through the schemitics and my theory is correct. I have to kill this backfeed and a diode will work famously IF I can get one that will handle the amperage. I did just think of something, why not use the second hole in the brake pedal support and put a seperate switch in for the brake controller? I think that just may work!! I have another switch in my parts truck. A few quick aligator clip connections to test it, then if it works just splice it in. If not, un clip it and find the elusive diode. Jim

[James McClure]

Originally Posted by 454HO

Try this pulse preventer

454: My good fellow, YOU NAILED IT!!! I recognize the part shown in the page you sent me to. It's a diode. For $14 bucks I'm going to order it. Description under the part is an EXACT fit to my issues. All you guys add this site to your favorites. LOTS of trailer stuff on this site. Many thanks, Jim

[454HO]

Glad I could help. That is a Draw-Tite part number 5501. You may can find it cheaper somewhere else. That is just where I saw it.