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Old 05-05-2012, 04:24 AM   #1
Join Date: May 2009
Location: Colchester, Connecticut
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Default Trailer wire Module DANGER WILL ROBINSON!

Bought a new trailer the other day. The seller told me that it had the round light connector, but he had a flat 4 conductor, and that he’d patch it in for me before I arrived. In my haste to depart and drive the 3 hours back home, I didn’t pay a whole heck of a lot of attention to what he had so graciously done, till smoke began billowing from below my steering column. Going into emergency management mode, I quickly pulled over, unplugged the trailer lites, and turned the key to “off”…..strange though, my little diesel just kept right on chugging away. Ignoring the keyswitch’s request to cease and desist!. The smoke was gone, and no evidence of ongoing damage. It was gonna be a long ride home that id better finish before dark. with no further damage evident, I made a run for it.
Once home, disassembly and inspection time. first shutting down by progressively removing fuses till the guilty circuit was determined. I found burnage in the fusebox, ok, so andy suggested a new fusebox from the dealer(Thanks andy) 150bucks in stock at the dealer . Still she ran till the fuse for horn/recirculation (upper fuse block) was removed HHHHMMMMMM so much for a simple solution.
An inspection of the taillight harness showed that the aftermarket trailer light interface closely resembled a fourth of July hotdog. (if I don’t laugh ill cry) the wires all looked like used sparklers too.
Next, I figured I better have a look under the seat. The cause was found there.
Apparently the helpful seller in his haste to offload this trailer figured if he matched the colors in his splicing that all would be well, however He must have connected the sprinter’s day running light circuit to his trailers ground, placing in inordinate load on my day running lites . I know , you say well why didn’t the fuse simply do the one thing it exists to do? My hypothesis is that when the trailer lite interface smoked like a hotdog it shorted internally the proceeded to short all my wires in the rear harness and spread forward like a plague. So the first question becomes why was there no protection in the interface? Then why didn’t a fuse in fuseblock #1 blow? I don’t know the answer, but I did find a wire (grey with a black stripe) going to a relay under the seat that also resembled an independence day sparkler. This wire was so damaged that I cut it out and spliced it, but even then she still ran w/key off….well, drastic circumstances call for drastic measures so I completely isolated it as best I could(It runs underneath and up the firewall in an inaccessible location) and I ran a separate wire from the relay in question up to fuseblock 1 ……. The grey/blk wire still had power from the horn/circ circuit but it wont matter as long as its not touching anything else.
Im very saddened that my sprinter has sustained such damage and I strongly urge all to add protection wherever applicable…..many thanks to andy for his help …..andy also says that an oem trailer light interface is available. Although expensive, it may prove to be cheap “Insurance “ as he says it has good internal protection.

Hope this helps someone else-Best Regards, Jim
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The Following 5 Users Say Thank You to bigjim499 For This Useful Post:
02bigcargovan (09-16-2012), aljimenez (05-05-2012), angolaron (05-06-2012), expcourier (05-05-2012), SewerRatz (05-06-2012)

electrical, fuses, trailer wiring

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