I 've got one .. this is baffling me.

I've got a '78 Starcraft pop-up camper. Whenever I hook it up to the truck and turn on my headlights, the cruise control stops working. The transmission also downshifts if I'm not using Cruise Control.

As soon as I turn the headlights off, everything works properly again.

I'm using a 7 blade to 4 blade adapter which is wired to a 6 pin adapter on the trailer itself.

Any ideas?

 

What is happening is that somehow the marker lamp 12V feed to the camper is sending power back one or both of the turn/stop wires. When your turn signals are off, the tail turn lights are connected to the stop lamp circuit. That 12V then goes to the PCM sense wire that tells the PCM that you're stepping on the brake. The PCM will cancel cruise since it thinks you're stepping on the brake. The transmission isn't downshifting, it is only unlocking the torque converter.

Do you have tail lights on the camper? If so I'd check the grounds first. If the ground in the camper is bad anywhere the return from the marker lights may be going through the turn signal filaments. Turn on the marker lights and hazard lights and make sure all of the bulbs work. If one is out, focus in on that.

If you don't have tail lights on the camper it could only be in the adapter to go from 6-4 since there are only 2 wires in the camper. In that case the camper wouldn't have the ability to mess with the turn signal wires.

 

Awesome information Joe. I'll check it out when I get home on Sunday. The camper does have taillights, so what you're saying makes alot of sense.

 

X2 on that Joe, I tried to rep you but NO dice


Im pretty sure that you are going to find out the issue. Good luck.

 

OOOPS double post

 

X3. I bet if you turn your lights on and then plug the camper in that your brakes lights will come on

 

You might try another adapter,sometimes you will find one that is wired different.

 

I got him for you Jose, good one Joe. I finally bought a set of those wireless tail lights when I have problems. They do come in handy.

 

Finally got a chance to look at this last night. Plugging in the wiring harness did not turn on the brake lights.

What was strange was that when I stepped on the brake, the tail lights actually went out on the camper, then came back on when the brake was released. I traced it to one of the bulbs. I'm going to replace both camper tail light bulbs today. I'll let everyone know if this fixes it.

 

If the trailer is a 6 pin, and all 6 wires are used you will need to get a 7 pin to 6 pin adapter. My 7-6 adapter does not pick up the center pin for reverse. Using 2 adapters, in my experience, causes more problems to chase w/ the wiring of the truck & trailer compatability. Unplug the trailer & adapters from the truck, check all the bulbs on the exterior of the truck checking one function at a time, then multi functions. If all OK, check the truck's trailer plug w/ test light for each function. Using a 12V battery not hooked to anything, hotwire each wire on trailer connector one at a time w/ a ground hooked to the trailer to check its 'function' and that it works. Make sure you check the ground you hooked up first w/ a test light to make sure you are grounded. You mentioned a bulb problem, this is where I like to start when I have trailer problems on a borrowed trailer as sometimes they have sat a long time or a bulb is burned out w/ one filament contacting the other causing a short or backfeeding through the other circut. I also agree w/ prev statement that not all converters are the same, I've seen cheap 7-4 that use the electric brake pin to feed both L & R brake & turn lts on trailer w/ no actual L or R turn signals or they try to use the L & R turn w/ Elec Brake and cause back feed through truck.

 

The trailer has a 6-pin plug on the camper side, but it's only wired for 4 pins to the truck (not my wiring). I've got another pop-up camper (same brand) that is wired for 4-pin and that one has no problems with the adapter I've got. There is little/no difference between the campers electrically.

 

Check bulbs like you were going to do. Once opened I'd just put in new ones. If PO wired trailer for 6 pin using 4 wires & you normally use a 4 wire I'd just rewire trailer back to a 4 wire flat. Good luck & keep us informed.

 

If both bulbs are doing that then you've got an open ground in the camper.

 

I replaced both bulbs tonight before we left. All is well!!

We went from So. Mn to Sioux Falls (about 3 hours). Not a single hiccup. Torque Converter stayed engaged and cruise worked the whole way. Hopefully the rest of the trip is this smooth. Tomorrow we'll go the rest of the way to Custer State Park.

 

Glad to hear that, congrats. thanks for the update.