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Old 11-04-2009, 10:51 PM   #1
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electrical problem

I have a 28' toyhauler that i pull with an 06 ford f-250 powerstroke. The last two times i have hooked up the trailer, i have fried my alternator.The truck is fine until the trailer is plugged into it. I believ there is a short somewhere.I have searched for broken, burnt or pinched wires and can find nothing. I have two deep cycle batteries and an onan generator in my trailer. If anyone knows where i should start, i would appreciate it.

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Old 11-05-2009, 06:27 AM   #2
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It seems very strange to me that anything you plug into the 7-way connector could "fry" your alternator. There are (or should be) fuses for every item going thru the 7-way. We used to kill alternators when jumping off someone while having the source vehicle running. What happens is that just as the jumped off vehicle starts the alternator surges and backfeeds the source alternator causing it to short the rectifiers.

The only thing I can think of is if you were plugged into shore power and plugged the TV (tow vehicle) in before disconnecting it, or if you're running the generator while the TV is plugged in to the RV. If either is the case then the converter could be bucking the alternator.

Have you plugged the RV into another vehicle to test it??

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Old 11-05-2009, 10:30 AM   #3
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Originally Posted by Bama Rambler View Post
Have you plugged the RV into another vehicle to test it??
Excellent advice. Also know that a very large percentage of electrical problems is due to faulty grounds. Check the ground wire between the TV and trailer, make sure the ground at the trailer is secure and you have good continuity. Faulty ground wires can cause some really weird symptoms.
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Old 11-05-2009, 10:55 AM   #4
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as a self proclaimed ford expert
the 7 pin plug has its own circuit breakers/fuses
did someone splice a new conncetor into the wiring?
and how is it frying the alternator>? is it making it charge at an high rate?
if so are your trailers batteries hooked up correctly and are they not damaged

the factory 7 pin only gets power + 12 volts if the engine is running and the relays had engaged.

I would wire check the trailers wiring as mentioned
double check the condition of the batteries and that they are not hooked up backwards

i would also wire check your factory 7 pin hook up
do you have the factory brake controller as well?

i would also go find another rv to plug into and see what happens

keep us informed
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Old 11-05-2009, 09:21 PM   #5
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no fix yet

My truck has the factory brake controller. I tested both rv batteries and they tested fair not bad. I hooked a ground wire from my rv plug to the ground off a battery and a power wire with an inline fuse from the battery, i checked all of the other prongs on the plug and all lights worked and it did not blow the inline fuse, so im not sure if i have a short in the trailer. I used my trailer in june when the 1st alt burnt up. My truck has been fine since, until sunday i hooked it up again and there it went. No idea what to look for next.
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Old 11-05-2009, 10:14 PM   #6
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Try disconnecting the generator. Who connected the generator and to what? Does it charge the batteries? That might be where your problem is. May need a steering diode installed to keep the truck alternator from "back-feeding" the battery charge circuit of the generator. Can verify by disconnecting the generator and trying it again, although I know alternators aren't cheap and you can't afford to keep testing. You might try to temporarily install a 100 amp fuse or circuit breaker in the large red wire on the back of the alternator. This will protect it while you look for the problem.
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Old 11-16-2009, 08:06 PM   #7
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Make sure your batteries are hooked up pos to pos & neg to neg. If not, you are running a 24 volt system. If your batteries are "fair" you might be somewhere between 12 & 24 volts.

Make sure your batteries are hooked up correctly. White is negative is black is present. Black is negative if red is present. Your trailer will pretty much function normally for a little while if the batteries are hooked up backward. If you use a generator or plug into shore power when you camp, it could take a long time to discover your problem.

I agree with most of the other stuff that has been said above, also. Check easy stuff first.

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