Can't Set Idle

[jzack]

A few months ago I could no longer set-up my idle when my low air buzzer is on. Now recently I noticed my parking brake dummy light no longer works even with a new bulb. Could these two problems be related?

I traced the bulb wire to the senser/sender under the dash above the brake pedal. There is no continuity between the tabs on the senser even with the parking brake applied. Is this good enough evidence to replace the sensor or should I check it with a mult-meter? If so what is the test procedure?

Again this is a 94 CH w/v-mac1 and unfortunatly I dont have a code-checker. Any help is greatly appreciated.

Thanks, Jeff.

[Terry T]

When I started driving the '95 CH613 Wrecker I was suprised when I could not idle up while the low air buzzer was on. This truck belonged to the Mack/Volvo dealership so I asked the senior mechanic about it. He stated that as long as the brake lights are on, the cruise will not set, and until it is aired up the brake lights are on so he wired in an on/off switch for the brake lights between the low air indicator and the brake light switch. Flip the switch and problem fixed. This switch also had no effect on the brake lights from the pedal, so if I forgot to flip the switch back, I did still have brake lights. I am not a mechanic so I really cannot tell you anymore than that.

T.

[rw613]

change the switch

[jzack]

Mackdog- Thanks for the tip. I might try wiring in a switch if I cant find the root problem. I've been driving this truck since it was new and I know I used to be able to set idle with the buzzer on. Nice looking wrecker!

rw613- I'll try replacing the switch. Thanks!

[Mackpro]

Raise the hood, below the windshields, look at the "cowl" "the black plastic piece that goes across the cab" On the bottom of the cowl, above the valvecovers there should be 2 rubber snounts that hang down( about 2 inches long). These snouts are water drains for the cowl. These snouts get plugged up with dirt and flies and trash, the water cant drain out of the cowl and then the cowl fills up and water drips into the cab and lands right onto the parking brake sending unit (above the throttle pedal) We see this all the time, remove the snouts and clean them out and replace the sensor and your fixed.

[jzack]

Raise the hood, below the windshields, look at the "cowl" "the black plastic piece that goes across the cab" On the bottom of the cowl, above the valvecovers there should be 2 rubber snounts that hang down( about 2 inches long). These snouts are water drains for the cowl. These snouts get plugged up with dirt and flies and trash, the water cant drain out of the cowl and then the cowl fills up and water drips into the cab and lands right onto the parking brake sending unit (above the throttle pedal) We see this all the time, remove the snouts and clean them out and replace the sensor and your fixed.

Thanks Mackpro