Yikes. My sympathies. Many sympathies, even if I don't understand why the fuse doesn't protect from that.

"Connecting the other terminals to ground is okay. Nothing will happen because there is no power in the circuit." Won't there be power in the circuit if the wire is attached to the trailer battery at the other end? The trailer ground is still firmly bolted to the frame.

Thanks also for the tip on the right signal - I'll be very happy to get that far.

I'm assuming that it is immaterial that the trailer batteries are not hooked up in any way, except for the test lead when tapping for test juice.

 

Terminal X jumped to Terminal Ground won't jurt anything, unless Terminal X has voltage(there shouldn't be one on the trailer plug, except maybe the one that charges the battery from the truck??). Ever go to undo battery terminals and accidentally touch both terminals with the wrench? You get a spark because you are completeing the circuit. With a 12v neg system, the ground is always connected, and then you energize(apply power to) a circuit (i.e. light bulb) it comes on. So, when you jumper a terminal to ground, nothing will happen.

Here is what I would do.

You know which terminal is ground. Take a jumper from that terminal to the frame, bumper, or ground terminal on the truck. Turn the parking lights on(constant 12v source). Take a jumper from the corresponding terminal on the truck to the other terminals on the trailer plug. Write down which is supposed to be which and which is actually what(if they happen to differ). If something should be wrong, the fuse for the lights on the truck will blow(I doubt it if the grounds are good). Once it all matches up, plug the trailer into the truck and verify the turn signals, etc.

By writing which is what, if something should be different, it will be easy to fix in the trailer plug.

Does this explain it better?

 

Thanks for your continued patience. I'm going to try to stick with the trailer independent of the truck until I'm at least posititve about the ground at the trailer. You say I've got that, but my readings as reported didn't convince me.

First I need to vote and have some lunch.

Thanks much, Joe.

 

What I mean, for example, is that the 'brake' terminal gave the same '0' reading as the 'ground,' so I can't be sure of either.

After doing some more ground searching, I'm going to fix a jumper to the trailer battery and juice each other terminal on the trailer plug.

And I guess I'll do that even if I don't get satisfaction with the ground search, as I understand you to say that would be OK.

 

I will have to check on the brakes. The magnetic coils have two wire, one source(from controller) and a ground. I will check to see if that circuit is supposed to go to ground. My understanding is that the more voltage applied, the stronger the magnetic field is and the stronger the brakes are replied. You won't be able to tell if the brakes are working unless you take the drum off. Don't test that one until I get back with you on it.

No worries, we all began at the same place, just at different times.

 

Ok, I have found a few sites that might help you some more. Also, it appears the the brake terminal should have an ohm reading of 0. Also, they said that you can test the brakes by applying voltage to them and that you should hear them "click".

Here are the two sites:

www.rverscorner.com/wiring/index.html

and

www.affiliateam.com/wiring.html

Hope this helps and let us know if whatelse we can do.

 

Most RV and trailer dealers will check out your system for free. They have a test set that plugs into either the tow vehicle or the trailer and can diagnose most problems in a couple of minutes.

 

Joe, thanks much for the follow-up on the brakes being OK with a resistance of '0,' and that I should hear them clicking with juice applied. At some point earlier on I had no success with that. I'll try it again.

And thanks also for those links. I'll check them pronto.

 

Thank you Shorebird, for the info. I have dealers within 25 miles.

CR Brophy makes a little tester (F7CT) which I cannot find locally, but which I could order. Problem may be that it is for checking the truck side and is female?

http://www.crbrophy.com/elec.html#f4ct

 

You may need to replace the magnets in the brakes. They may be worn out.

I know dealers check, and usually for free, but I figured that since it is illegal to tow something without brake lights in many states. You could probably get away with it(tell officer you are taking it to a dealer to have the check the wiring). Just do not do it any where close to dawn or dusk, full daylight only.

The RV store might have testers too, to loan you. Just an idea.

 

Thanks, Joe.

I was thinking of getting an emergency lighting rig to have for back-up anyway, and for use to get to a dealer for check-out. My guess is the check-out might not be so helpful, depending on how much diagnostic info comes with it.

Firmly grounding at the trailer lead to these results when testing for resistance at the trailer plug:

ground: 0
brake: 0
right turn: .3
power: 0
tail: 0
left turn: 90 to 120 fluctuating

Applying trailer battery juice to the leads at the trailer plug did nothing, so naturally I thought maybe the batteries were dead. Checking them with the meter set to DCV 20 with red wire to battery jumper and black to ground resulted in a reading of .28 to .30, which I don't know how to interpret.

20 X .30 = 6 volts???

I've got to go away for a few days (I had hoped to tow the trailer). When I get back I'll search for 'Multimeters for Dummies."

 

check the pins for voltage first, then you can check for ohms(if the pin has voltage it could hurt the meter)

 

Sounds like a basic and very important tip.

Thanks.

 

OK, I now know that the voltage reading of the trailer battery was as indicated (no mutiplication required; the DCV range setting is just an upper limit) : .30 volts, so I'll pull and charge them.

 

Sorry, it's been awhile since I had a chance to check this. Yes, the settings are just upper limits. When testing ohms, always set it to the highest range on the meter, unless you KNOW what you are looking for.

Charge the batteries(it may take awhile since they should be deep cycle), check for voltage at terminals like mentioned. If no voltage at the terminals, you should be okay to jumper power to them.

Let us know how things turn out.

Good luck