40amp tow fuse blows/loss of brake/turn signals

[RockyMtnRay]

Originally Posted by Steverino

Thanks for your thoughtful responses...

I did some further checking (& sweatin' - jeez what a sticky day!)... Anyway, I found some bullet connectors on wires under the trailer - coming from the fridge area and going up the rear shell arm. Tested and got current on the two that are for the brake & turn signal lights. So I guess the next step is to check for continuity from that point to the light socket. I am presuming I'll find a broken circuit. The odd thing is that BOTH lights are misbehaving and they would not be linked (since they operate independently). I can't yet figure out the connection.

I'll be reading the suggested links for further clues.

Thanks,

Steve

The trailer uses a 2-lamp (actually 2 filament) tail/brake/turn system: the turn and brake display on each side is performed by the same filament in the same bulb (the other filament in the bulb is for tail/running light). Your TV uses a 3 lamp system (separate bulb or filament for each purpose)...there is a converter in the TV that converts the 3 lamp signals to 2 lamp signals. Since
brake/turn don't work...but there is a signal going to the bulb, you either have a bad lamp fixture with corrosion (not surprising on a '99 model in the Northeast) or you could have a bad ground coming back from the fixture. Remove the lamp cover and bulb and start checking for signal there as well as if there's good continuity (will require an ohmmeter) on the ground side (typically the connector attached to the base of the bulb).

I've checked both TM taillight assemblies:

The dual-filament bulb does both a running (or parking) light (filament #1) as well as the brake & turn light (filament #2). On both taillights, filament #1 works fine. This would seem to indicate that I don't have a ground problem with the light assemblies. Filament #2 is dark on both assemblies.

And I know that I have current from the T.V. to each brake/turn circuit before the wiring loom goes into the rear shell. (Tested w/voltmeter with turn signals on.) All other rear shell lights seem to work fine.

So, unless my logic is faulty, something has severed the connection to each brake/turn circuit somewhere from the base of the rear shell arm to the taillights. But whatever it is didn't affect the rest of the wires in the loom??

More investigation to follow this evening!

Steve

Not to sound too simplistic, but have you tried new bulbs? Some times those cheap 1157 bulbs look good, but the filament is actually broken - something you can't see until you tap on the bulb and one end of the filament bounces around because it's not connected. I've even had them bounce over and hook up to the other filament and then you have all kinds of fun trying to figure out why your running lights flash with your turn signals! Grounds on RVs have always had problems, too, but if your running lights are working it's probably not a ground problem. Have you checked the wiring where it goes into the lifting bar on the left side? That always seemed to me like a place for problems to start with the wires flexing when you set up or lower the shells.

Okay, so here's the latest...

Found two apparent problems:
1. Right TM taillight: The bullet connector under the trailer (near the fridge) for this side seems to be somewhat corroded - it shows continuity, but unless it's twisted just right not enough current gets through. I am not surprised - those bullet connectors can be bad news.

2. Left TM taillight: Traced back to the 4Runner. No current at the factory hitch's 4-prong connector. Followed that loom back behind the left rear inside trim panel & found a little black box - one plug in, one plug out. It's called a 15 amp taillight converter auto circuit protection, and is a Toyota product. I'm not sure exactly what it does, but when I tested the output with a voltmeter, the right side was great, the left was very low. I checked the "input" plug and got full voltage for both sides, so I think I've found the culprit. I'll call the dealer tomorrow to see about getting a new one.

My only puzzlement now is did I (or the TM) do anything to blow out this circuit in the box, or did the box just give up the ghost on its own?

Maybe my conversation with the parts guy will shed some light on this...

More news as I get answers...

Steve

Called Toyota dealer & they wanted $191 (!!) for the taillight converter. Found out that one needs to be careful how many amps are being pulled through the converter or you risk blowing it out. Of course there was nothing about this in the owner's manual! I still don't know what the Toyota's maximum amp recommendation is and am curious about other manufacturers. When we get another TV, you can be sure I'll be checking about this before hooking up!

Anyway, checked around online and found a Hidden Hitches heavy duty 20 amp converter at Hitches Online for about $60 including a power wiring kit and tax. The 20 amp may be overkill, but I wanted to be sure. Now I am drawing power directly from the TV battery to power all the trailer lights. Wired everything up last night and things seem to be working much better.

The only things left to do are:
1. Find some way to eliminate corrosion on the TM rear light assemblies (inside the bulb sockets), & prevent it from returning. Could dielectric grease help??

2. Eliminate the &$*@# bullet connectors that link the two shell looms to the main wiring harness under the trailer. Those connectors are a problem area and an ideal spot for bad connections to fester. Since I can't imagine ever needing to disconnect the shell looms, I may just solder all of the connenctions & eliminate the bullets altogether.

Thanks again for everyone's good suggestions - they did help me eliminate various possible problem areas.

Steve