usrjcro11

This is describing and solveing a problem. Truck started cutting on and off going down road after starting up and going about a 2 mile. Tried shutdown override and did not help. All gauges looked good and radiator full. Truck finally quit completely. Started testing with power probe cab relay and starter relay on firewall and would turnover. Disconnected positive battery cable and was getting 12 volts on cab relay with key off on negative side. My multimeter was shipped to fluke for repairs. I said it must be a capacitor somewhere that hasn’t completely discharged. Hooked farm service truck to truck and lowboy and ran air hose to services tanks on truck and pulled it home about 2 miles because getting dark. Next day remembered I put negative firewall relay on other truck but could not explain 12 volts. Took relay off 91 model and installed on 94 model. Went to hook up positive battery cable and found problem. Crossover positive cable had rubbed on battery box and had gone to ground. The ground relay had done its job. That explained 12 volts on negative side of relay but probably few amps knowing all I had was power probe on battery. Live and learn. Simple things first.

Sorry for being late updating post. New valve corrected problem.

I will be ordering new valve tomorrow. will update when I get it in and replaced. thanks

Well you both are correct. Lines are backwards. I was just hooking to old lowboy trailer whichever way made brakes release. No color codes on trailer.Am I correct by saying no air should come out of either hose without trailer service valve pushed in? If this is correct then is trailer protection my problem with air coming out of trailer line without trailer service valve pushed in? thanks

This was problem. Truck had been sitting up for about 6 months. Exhaust line was plugged. Took exhaust line off and it worked. Thanks all that contributed. Newbie in learning curve.

I will do some testing tomorrow. Thanks all for replies. Will report back

Correct

Sorry to confuse. Two separate issues.

I knew what it was suppose to do but my air bags never purged air to assist uncoupling from trailer.

The air bags do not start raising till about 90 psi. Same time as air bag on cab starts raising.

Yes I can tell when bags are inflated after air builds up.

Will test tomorrow. Where should the air exhaust from if switch is working properly? Leveling control valve? Behind dash? Wondering if I may have a plugged exhaust line. Dirt Dobbers are bad here plugging lines. Had a international truck with vacuum assist brake. Brake pedal hard but no brakes.put new booster on no better. Found exhaust line plugged from dirt dobber. Learn expensive lesson.

I will take pictures tomorrow up and down. Noticeable difference.

Mechohaulic fully understand. Need all help I can get

When I flipped switch another person was by fifth wheel and did not hear any air discharging nor saw airbags go down.

.how long should it take to dump air? Maybe I did not wait long enough. Should air come out of exhaust port on leveling valve?

There is a leveling valve on front drive axle. I had dash apart looking for air leaks. Truck and trailer air supply buttons have airlines coming into the back of them. No wires

Yes this 1994 truck has airbags on suspension.

Do not thinks it is because airbags adjust without trailer valve engaged. i do have another problems I posted that is separate from this one.

My problem it is not dropping air bags. Am I suppose to do something else after flipping switch? Newbie here my 1991 Mack ch does not have airbags.

Yes raising protected cover and flipping switch up. Sorry for confusion

Raise the cover and toggle up on this

Unhooked from lowboy trailer today. Discovered air coming out redline when I press brakes without trailer air supply engaged. When I engage trailer air supply air comes out of blue line for trailer which I understand. Is air supposed to come out of the redline with trailer air supply off? If not what do I need to check? Thanks

When I lift switch cover and toggle switch up nothing happens. When I toggle switch down a little bit of air discharges behind the dash. How does this switch work. Bought truck about 9 months ago just now trying it. How do I go about troubleshooting? Thanks