Not sure If I'm posting this in the right area or not, but maybe someone can give me a hand. I am on the volunteer fire dept. here at home and we have come into the posession of a 1981 International Harvester medium duty truck(badges are faded so not sure what model.)
We have had the truck for over a year now but we have been short of time and (VERY) short on money so it has been sitting empty and with out a pump in the yard of the fire station until last week. We recently got a grant from a very generous community group in Wichita Falls, TX that allowed us to purchase two new pumps for our brush/grass trucks so I have taken one of the old ones that was still in good shape and put it on the tanker.
Now to my problem, from the time the air pressure comes up enough to actuate the brakes until it drops below or you cut the power, the brake lights (actually only one) stay on. I'm by no means an airbrake or wiring genious so I'm having trouble figuring out where to start my trouble shooting. I think that the right brake light doesn't work because of a short in the wiring to the housing because the bulb is good and the tailight works but I'm not sure. The blinkers also have some problems. The left blinker works intermittently if you jack with the switch, and the right blinker won't work at all. I assume that this is due to a faulty blinker switch. If anyone has any ideas I'd sure appreciate the help.
Nick

 

it will probably be your brake lght switch,small air switch thats simualar to a low oil switch,if i remember right i think its on your treadle valve.there is also one for low air press,so make sure you get the right one.should be a normally open.hope this helps

 

Thanks,
Can anyone tell me where exactly to look for this part on the valve?

 

First off before you go tearing into things check this first. Start and run the engine to build air pressure up to 120 psi, shut the engine down but leave the ignition key in the on (run) position. Chock the rear wheels so the truck will not roll, then release the maxi brake, go to the rear and see if the brake lights are still on. A lot of older trucks came set up so the brake lights would be on it the ignition was in the run position but the brake was set to the on position. Verify this before you do anything else. As far as the directionals go, it is most likely the switch assembly, they love to go bad. It is still a problem to this day.

Repost what you find, we will help you get it straightened out.



Tim

 

Our 75 mack is like that as long as the E-brakes are on then the brake lights are on and anytime the air pressure is below 60 they are on but once the pressure is built up and the e-brakes are realeses they work like they should. Also I have everything needed to build a pumper at the house (tank, pump panel, complete rear assembly) if you are interested in it shoot me a pm.

 

Just a bump, How did you make out?

 

Been busy with work but I'm going to work on it today. I'll let you guys know in a bit. Thanks.

 

Well...I figured out it wasn't the parking brake being set. other than that I found that whoever wired the lights on the back when they retro fitted the tanker body onto the truck was completly and totaly incompetant. In a 6-8 foot horizontal (3ft straight from the original tail/brake lights) they managed to use 4 or 5 different wires in three sizes and never managed to hook up the same color wires in a given strand even when they were available. It took me 45 minutes to trace the brake light wire that short of a distance with virtually none of the wire being obscured by anything other than black electrical tape. Now I need to get into the light where its tied in and see why I'm only getting .1-.2 amps out of that wire when the other brake light manages to stay on constantly. Who thinks another wiring job is in my near future As for that pressure switch on the treadle vavle, can anyone give me a little better idea what I'm looking for? I looked at it when we had to replace it to get the truck to move but I don't remember taking any wires off of it and the lights were staying on before then. (by the way I didn't put the valve back on a qualified mechanic did it for us)
Thanks Guys
Nick

 

Is that brake switch on the Firewall? Got the lights all workin

 

It is most likely installed on the treadle valve. Some switch's look like oil sending units, some are square but still screw into the treadle valve assembly. Just look for a switch with 2 wires going to it on the valve. If the valve penetrates the fire wall, (some do, some don't), then the switch may be mounted to the valve from the fire wall side.



Tim

 

Well guys, I have gotten everything but the brake light switch. Even the International dealer can't figure out where its suposed to be. There is no switch on the treadle valve, or the compressor. the lights are off until it builds a little pressure and actuates the switch so I know it hasn't been taken off and lost. Talk about a PITA