Troubleshooting cruise control issue

[DrKessler]

Next up on my list of projects for my 87 k5 is to try and get the cruise control working. I think i have a direction to look first, but don't know how to go about it. So I noticed when I was replacing dash bulbs the bulb for brake light was missing. Didn't think much about it, but when i put a bulb in there it would stay lit up all the time when blazer was running. Didn't recall any brake issues at the time so i just removed it instead of trying to look into it more... Now I'm thinking the fact the brake light is essentially always on if a bulb was in it, that that could very well not allow the cruise control to engage. Seem plausible? So how should i go about troubleshooting the brake light? Parking brake engages and disengages normally i feel. I've seen a proportioning valve being mentioned that could be an issue. i located it under the fan shroud, no leaks. i tapped it with a hammer, but that was it... There is an electrical connection on it. I didn't know if i could just remove it and see if the light goes off, and cruise works? Do i just pry it with a screwdriver to remove it? I attached a pic of an example for reference.

If anyone has any different thoughts on where i should look, i'm all ears.

 

[frankin5]

If you remove wire from E brake and from the proposing valve and still have a lit bulb, you have a short in circuit. The bulb circuit is completed by a ground source.

 

[frankin5]

In the cruise control problem, make sure the switch on the brake pedal is set properly.

 

[Wes Harden]

The red brake light in the instrument cluster is turned on for 2 reasons.

1 the parking brake is set.

2 the hydraulic system has a pressure imbalance.
Neither of these will effect the cruise control.
You really should find out why the light is on.
If you remove the wire from the proportioning valve(squeeze wire connector and pull) and the light goes out, the shuttle in the P valve is off center. Could be as simple as bleeding the brakes, to fix. But the system should be inspected for leaks.

As fast the cruise control goes, is it factory or aftermarket dealer install? Electronic or mechanical?
Many reasons why it might not work. As mentioned above the brake switch adjustment could be it. Do you a a 700r4 transmission in this truck?

 

[DrKessler]

The red brake light in the instrument cluster is turned on for 2 reasons.

1 the parking brake is set.

2 the hydraulic system has a pressure imbalance.
Neither of these will effect the cruise control.
You really should find out why the light is on.
If you remove the wire from the proportioning valve(squeeze wire connector and pull) and the light goes out, the shuttle in the P valve is off center. Could be as simple as bleeding the brakes, to fix. But the system should be inspected for leaks.

As fast the cruise control goes, is it factory or aftermarket dealer install? Electronic or mechanical?
Many reasons why it might not work. As mentioned above the brake switch adjustment could be it. Do you a a 700r4 transmission in this truck?

Thank you. the cruise is factory i believe, and mechanical meaning vacuum pressure and what not, and yes 700r4 transmission.

 

[Wes Harden]

I expect there is vacuum controls for the 700r4 and the cruise. Would not be surprised if they were mixed up under the dash.

I hope you have electronic control, should be easier to fix.
The mechanical has a transducer that uses the speedo cable for a speed signal. Very finicky, and no longer available. If you have this, and want cruise possibly replace with aftermarket.
The electronic has a module at the vacuum actuator and get it's signal from a VSS, vehicle speed sensor,