Karl Townsend wrote:

I bought a brake controller that uses a sensor in the brake line. Today, I
took the brake line apart at the master cylinder, installed the "T" and
sensor. Had my better half pump the brakes while I bled. No big deal, I
thought.

Well, as soon as I started the truck, the brake warning light came on. So I
had the better half pump the brakes while I bled a whole can through the
front wheels. No joy.

I called "the Kid". He said to get a vacuum device from bumper bumper for
only $20. Well, it was $50. But I got it and bled a can through each front
wheel. No sign of bubbles at all. Note: the sensor is on the front set on
the tandem brakes

Still no joy. I got a brake warning light. I just got ****ed and called it a
day. What do I do tomorrow?

Karl

This is why there are few aftermarket trailer brake controllers that tap
into the trucks brake system in any way. It's a big product liability
insurance issue modifying the factory brake system, and it's also a big
DIY installation issue with people not having the correct manuals to
bleed the brake system properly.

You finally said it's a '93 Ford 350, I'm not familiar with them, but
it's recent enough that it may have an anti-lock brake system. If it
does it may require a special bleeding procedure requiring a higher end
scan tool, and I believe it's pre-OBDII, so it's not very standardized.
As someone noted, you need to bleed and dead end line to the pressure
sensor, or you'll have an air bubble stuck there.

I believe Autozone has some manual pages available online for common
procedures like this. You can also buy a subscription to Alldata DIY to
get access to the manuals. You can buy the factory manuals from HELM.
You could try one of the cheapo manuals from an auto parts store, but
you take your chances with them vs. the factory manuals.