'7427 PCM not receiving brake switch input

[PlayingWithTBI]

No worries, the “normally open/closed nomenclature” is a bit confusing for a switch that in the normal state has the button pushed. I think my factory cruise system does use vacuum tho - the switch originally did have a vacuum line attached to it.it’s still under the dash, plugged.

sounds about right. So there’s no vacuum at all on the GMT400 cruise system? Uses an electric control to open and hold the throttle? That’s the system I want to convert to but I have the stuff from a vortec truck.

On the "Normally Open" terminology in this case it would be normally open held closed. The switch springs to open when released.

IDK if the 96+ cruise gets the same signal as the 88 - 95. I think 96+ is 4,000 PPM where 88 - 95 VSS is 2,000 PPM? I don't know about 95, it was an odd year.

[tayto]

91 suburban is a squarebody, not gmt400 platform. if you have a vacuum diaphragm near the throttle linkage, then you're other brake switch should have a vac line. I removed a dash and engine harness from a 1990 suburban a few months ago and it had same cruise setup as my 86.

[Daveo91]

On the "Normally Open" terminology in this case it would be normally open held closed. The switch springs to open when released.

IDK if the 96+ cruise gets the same signal as the 88 - 95. I think 96+ is 4,000 PPM where 88 - 95 VSS is 2,000 PPM? I don't know about 95, it was an odd year.

Hmm, I'll have to check into that. I was under the impression the vortec system I have would work. Thanks!

91 suburban is a squarebody, not gmt400 platform. if you have a vacuum diaphragm near the throttle linkage, then you're other brake switch should have a vac line. I removed a dash and engine harness from a 1990 suburban a few months ago and it had same cruise setup as my 86.

Yup, I know my 91 burb is a squarebody. Burbs, Blazers, crew cab 1 tons all stayed square until 1992. All other pickups started with GMT 400 in '88. I was just curious if they changed to the non-vacuum cruise in 88 with the first GMT 400s. My '91 definitely has vacuum cruise, but I want to eliminate it and go with the electric system. It will be much easier to mount on my non-stock intake manifold and just seems more reliable than the vacuum system.

BTW, on a different thread we were talking about my burb's DRAC/VSSB. You were right, it's mounted to the backside of the dash, under the radio. I had my radio out recently for something else and there it was.

[brian617]

The later DRAC is capable of outputting either 2000ppm or 4000ppm.

There are some diagrams in this thread,

http://gearhead-efi.com/Fuel-Injecti...t=drac+diagram

[Daveo91]

The later DRAC is capable of outputting either 2000ppm or 4000ppm.

There are some diagrams in this thread,

http://gearhead-efi.com/Fuel-Injecti...t=drac+diagram

Awesome! It looks like my '94 vintage DRAC should be able to supply the 4K output then. The diagram in that thread shows that it would go to terminal C4. Thanks.