1988 Suburban CRUISE CONTROL HELP!

[Frankenchevy]

I know I’m missing parts, just not sure what.

I know I need the doohicky that pulls on the throttle lever at the TBI, but that’s about all I know…

Can you guys help with pictures and locations of what parts I need. I’ve searched, but not having much luck coming up with stuff specific to 1988. I’m fairly certain I need a transducer that goes on the DS inner fender, but maybe TBI doesn’t have that?

Here’s what I see that may be related…

This hose that goes into the firewall:

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This connector:

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Maybe this is related from the interwebs?

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[Frankenchevy]

I found this for the servo, but I don’t remember seeing any flat 5 pin connector in that area.

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[bucket]

Iirc, the cruise control setup is a complete stand-alone system in the TBI years. There's a control module, that last servo you posted, and a harness. No transducer inline on the speedo cable like the older ones.

 

[Frankenchevy]

Any idea if the harness pictured above has something to do with cruise?

I think the large tube connects to the servo and I’m guessing this T used to, as well.

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[bucket]

Any idea if the harness pictured above has something to do with cruise?

I think the large tube connects to the servo and I’m guessing this T used to, as well.

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I don't remember, I'd have to go look at my '88. With any luck, I'll be home before it gets dark tomorrow and I can take some pictures.

 

[Matt69olds]

There is a jumper harness that goes between the square connector and the cruise servo.

There are 2 vacuum lines, the smaller line is the supply line from the engine. There should be a round storage ball somewhere under the hood, there will be a check valve between the storage tank and the engine. The larger vacuum line goes from the servo to the brake switch under the dash. Hit the brake, the vacuum switch dumps vacuum to the servo and releases the throttle.

Before investing too much time in this, make sure the cruise control box is still under the dash. It’s clipped to a bracket above the throttle.

Cruise control on these trucks is a plug and play option. The hardest part about putting cruise on a truck that didn’t have it is putting the switch in the steering column. The cruise harness is completely seperate from the rest of the truck. The main power feed plugs into the fuse box, the speed sensor input plugs into the vss on the back of the speedo head, the brake switch mounts to its own bracket on the steering column support bracket, and other than the main supply line the vacuum hoses are wrapped in the main harness. If you have a parts truck it’s super easy to add the option to a truck that didn’t have cruise.

 

[YakkoWarner]

I have all the components in the cabin (column switch, under dash control box and brake pedal switches), but everything except the vacuum resiviour ball on the engine bay side was removed by previous owners. I'd love to see some pictures of the completed system because that would help me know what I am missing. Not that I have much hope of finding the parts but knowing what to look for is step 1.

 

[Frankenchevy]

I have all the components in the cabin (column switch, under dash control box and brake pedal switches), but everything except the vacuum resiviour ball on the engine bay side was removed by previous owners. I'd love to see some pictures of the completed system because that would help me know what I am missing. Not that I have much hope of finding the parts but knowing what to look for is step 1.

I’m in a similar situation. Pictures would be very helpful. Sounds like Andy might be able to take some pictures for us at some point when he’s near his ‘88.

There is a jumper harness that goes between the square connector and the cruise servo.

There are 2 vacuum lines, the smaller line is the supply line from the engine. There should be a round storage ball somewhere under the hood, there will be a check valve between the storage tank and the engine. The larger vacuum line goes from the servo to the brake switch under the dash. Hit the brake, the vacuum switch dumps vacuum to the servo and releases the throttle.

Before investing too much time in this, make sure the cruise control box is still under the dash. It’s clipped to a bracket above the throttle.

Cruise control on these trucks is a plug and play option. The hardest part about putting cruise on a truck that didn’t have it is putting the switch in the steering column. The cruise harness is completely seperate from the rest of the truck. The main power feed plugs into the fuse box, the speed sensor input plugs into the vss on the back of the speedo head, the brake switch mounts to its own bracket on the steering column support bracket, and other than the main supply line the vacuum hoses are wrapped in the main harness. If you have a parts truck it’s super easy to add the option to a truck that didn’t have cruise.

Thank you, this is definitely helpful. I’ll look for the cruise control box in the area you described. I already ordered the stalk, as it appears that was replaced with a non-cruise parts store job some time in the past.

 

[Frankenchevy]

@Matt69olds , this is what I see under there.

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[bucket]

@Matt69olds , this is what I see under there.

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I do believe it's the module circled in red:

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[edgephoto]

I have a 1987 V3500 7.4 TBI with cruise that I am currently restoring. I will be at the body shop tomorrow and will try to get you some photos.

Underhood there only is the servo, a short harness that connects servo to that square connector you have. The large vacuum line is the dump line and connects to a switch on the brake pedal. The smaller vacuum line is engine vacuum.

I am not sure if non cruise control vehicles have the vacuum reservoir but I suspect they do for the HVAC system. The check valve is connected so you do not lose the vacuum in the reservoir during low vacuum situations.

 

[Matt69olds]

I do believe it's the module circled in red:

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Indeed, that’s the cruise control box. if you follow the harness that plugs into that box, you should find the vaccum hose and brake switch connector.

The connector with the pink/purple wires should plug into a brake switch. That’s for the TCC, assuming the truck has a 700 trans.

 

[Frankenchevy]

Indeed, that’s the cruise control box. if you follow the harness that plugs into that box, you should find the vaccum hose and brake switch connector.

The connector with the pink/purple wires should plug into a brake switch. That’s for the TCC, assuming the truck has a 700 trans.

It has a TH400. Would that be a similar situation or something change?

 

[Matt69olds]

It has a TH400. Would that be a similar situation or something change?

That would explain why it’s unplug.

Th400 don’t have a lockup converter.

 

[bucket]

It was kinda still light out when I got home today.

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That's an '88, 4x4 Suburban with original small block.