Trailer Wiring

[Soundguy]

That's why i like the breakaway kits that use a charger module on the battery.. lil bit of logic in there knows when the truck is running or not by compairing stating bat voltage to alternator ( charge ) voltage.

soundguy

Mark and others, it is fine to do it that way but the problem is as the battery on the trailer drains it will pull down your tow vehicles battery if not running. It will not be a problem except if you were using a travel trailer or something similar it is possible to get in a situation where the tow vehicle will not start, like camping overnight with it still hitched up. Even a dump trailer hitched up the night before a big job may drain the trucks battery enough to not start in the morning.

Most factory installs and good aftermarket installs run it though a relay that allows it to only be hot with the tow vehicles key on or running. Prevents the above situation from happening. Trust me, it happens. My neighbor had a camper that stayed at a a remote property for a year. When they got there to take it home they hitched it up then spent the day having one last visit and cleaning up the site. When they went to start the truck and guess what. I got called out to drive 45 miles each way to jump start the truck. It was a 96 Dodge wired hot all the time and my guess as to what happened is the battery on the trailer was low and pulled a charge off the trucks battery. Got them both so low it would not start.

Chris

 

[JB4310]

Hate to say it.. but maybee.. as you mentioned in the first message.. you are unqualified to run that meter.

what's a testlamp show you on those pins..

soundguy

I was trying to be humble but no I'm not an electronic whiz by any stretch.

I do know basic wiring ac/dc I know how to check for shorts, open, ground, continuity voltage etc. I don't have a very good grasp of resistance and current, ok I never use that side of the meter

So are you guys saying I could have voltage readings but no current?

I will check it with my light, My meter is a decent RS unit. I lock the range hold so the decimal isn't floating, so that's not confusing me.

This truck does have a monster size ECM mounted on the side of the engine block, don't know if this wiring is controlled by it but I suspect it, I had a cargo light (up by the high stop light) that was mistakenly deleted from the truck order, even though the light is there the wires are there and the switch is there, the dealer told me there's no way to get it to work cause the ECM was programed VIN specific.
It was told there was not to be a cargo light so now there is no cargo light. they can turn it on with the OBD tester but not program it to work with the switch.

JB.

 

[RobertN]

I was trying to be humble but no I'm not an electronic whiz by any stretch.

I do know basic wiring ac/dc I know how to check for shorts, open, ground, continuity voltage etc. I don't have a very good grasp of resistance and current, ok I never use that side of the meter

So are you guys saying I could have voltage readings but no current?

I think maybe you are using the meter ok, but not getting a good ground when using it. I have seen funny stuff like that before.

Yes, you can have voltage but no current; that is an open circuit. If you have nothing connected to the truck, and are reading voltages at the 7 wire connector, you have an open circuit.

Make sure the meter is all the way to DC voltage. Sometimes I do not pay attention, and only switch to AC voltage; that will throw you off. I have 25 years of high tech electronics lab experience. I still get in a hurry and don't turn the knob to exactly where it should be.

 

[RobertN]

I like this site for 6 and 7 wiring diagrams.

Marksrv.com 7 way wiring diagram page

I like that they show the numbering for the connectors. I have seen the connectrs mounted upside down, and also at 90 degrees. Makes debug hard when referred to as 1 oclock, 3 oclock ect. All the 7 wire connectors/plugs/receptacles I have bought in the past had the numbers on them.

So this is the weird part, kind of a question and kind of just a statement. While checking my trucks 7 pin outlet I find I'm getting voltage from almost all the terminals except the running light blade at the 11 o'clock position and the ground.

Specifically as follows:
with key off, actually no key in ignition.

terminal at the 1 o'clock position, bat+ = 12.9 volts
term @ 3 o'clock, RT turn/stop light 8.9
term @ 5 o'clock, elect brakes 11.3
term @ 7 o'clock, ground 0
term @ 9 o'clock, left turn/stop light 1.3
term @ 11 o'clock, running lights .1
center terminal 3.9

with truck idling. but no lights on or brakes pressed.

term 1 o'c 14 volts
term 3 o'c 2.5
term 5 o'c 12.1
term 7 o'c 0
term 9 o'c .6
term 11 o'c .3
center term 3.9

 

[Soundguy]

Ditto what robert said.

I wasn't kicking you.. it's just that there are some electrical nuances that the average meter 'owner' aren't familiar with.. that's why I sugested a test lamp.. it's an easier go/no go test since it is much lower impeadance than the imput to that vom.. which will be many thousands of ohms.. and could show open circuit voltages that , when in circuit and loaded, simply wouldn't be present.. or would / could be quiescent leakage current.. etc..

soundguy

 

[JoelD]

I find myself using the little red light tester more often than my volt meter when wiring trailers. Just a lot easier for me to handle, has the nice sharp point to test wires anywhere without hooking up and unhooking up.

The test light works good for me and keeps things simple.

I think electrical is much more complicated than the layman (which I'm one of us) could ever imagine.

A good friend of mine is a master electrician, been one for 20 years, works on the big 1000 volt plus DC stuff in the tunnels for subways and the like, and to this day when I ask him a question about just how electricity works he'll say, you know, not many of us even totaly understand just how it works.

Joel

 

[Wis Bang]

Newer vehicles can feed back. When my S-10 shorted at the cigarette lighter the dome lamp had voltage coming from both sides. Thanks to a burned out brake lamp & a blown fuse. Computers multplex things so you couid have other issues.

Three summers of inspecting tractor tailers during, I was taught to never use the ground inside the plug. Always use an independent spot on the chassis...

Test lamps work well. Just never puncture wires with the sharp point. the tiny hole allows moisture to enter the wire & the resulting corrosion will wick along inside the insulation making problems.

 

[Soundguy]

I have added extra ground wires on qd ends to all my trailers 'just because'

soundguy

 

[JoelD]

Newer vehicles can feed back. When my S-10 shorted at the cigarette lighter the dome lamp had voltage coming from both sides. Thanks to a burned out brake lamp & a blown fuse. Computers multplex things so you couid have other issues.

Three summers of inspecting tractor tailers during, I was taught to never use the ground inside the plug. Always use an independent spot on the chassis...

Test lamps work well. Just never puncture wires with the sharp point. the tiny hole allows moisture to enter the wire & the resulting corrosion will wick along inside the insulation making problems.

Thanks for the point on puncturing the wires, been guilty of that.

Joel

 

[Soundguy]

electrical theory is fun, and frustrating.

past a 'layman' and basic use level for ac/dc stuff like 12v elec system and 120/240v single phase AC, which ain't all too bad... it turns into one of those things that you either really like it and get into the 'deep end' or you don't like it and stay in the shallow end.

soundguy

I find myself using the little red light tester more often than my volt meter when wiring trailers. Just a lot easier for me to handle, has the nice sharp point to test wires anywhere without hooking up and unhooking up.

The test light works good for me and keeps things simple.

I think electrical is much more complicated than the layman (which I'm one of us) could ever imagine.

A good friend of mine is a master electrician, been one for 20 years, works on the big 1000 volt plus DC stuff in the tunnels for subways and the like, and to this day when I ask him a question about just how electricity works he'll say, you know, not many of us even totaly understand just how it works.

Joel