International 4300 what makes hydraulic booster pump come on?

[kentuckynet]

hello, i have a 2002 international 4300 with hydraulic brakes, i was wondering what makes the booster pump motor activate?
I dont think mine is working as i cannot find any voltage at anytime going to the motor.
I checked all the fuses, it appears there is a 5am relay style fuse/breaker that says hydro pump boost, i switched it with another and still have no power going to the pumo motor.

im sure someone here knows the answer, thanks in advance and merry christmas

 

[Humble pie]

Man it’s been a long time and @Snowman_w900 or @Wore Out may know more. But I believe the relay is powered from the key switch. When it’s in the on position the relay should have power. But I could be wrong. I never worked on many of those systems

 

[kentuckynet]

I have the key on and the truck rung but theres no power going to the pump

 

[389 Hood]

Isn't it driven by a belt drive pump from the engine. Many GM, Binders and smaller KW's use a belt driven hydro-boost pump that is incorporated with the power steering system. If they went electric, that's a new one on me.

 

[r3gulator3]

There is a relay usually mounted under the pump that should have constant power at pin 30, the brake light switch supplies power to pin 85. And the pressure switch in the booster itself provides ground at pin 86 when necessary. Pin 87 supplies power to the pump motor. Most of the time the brake switch or relay is bad.

 

[r3gulator3]

The electric pump should work with key in any position and the truck not running or if the p/s pump fails it will work when running.

 

[ladyrig]

You should reach out to these guys on Youtube. They are super helpful if you ask a question in the comment.