So I've got everything removed from my 89 for the C6 conversion. I'm curious why the clutch pedal has an electric switch to disconnect the cruise control but the brake pedal has a vacuum switch?
The brake pedal actually does have an electric switch for the cruise, it just ain't a stand-alone one - the cruise brain box receives signal from the brakes switch, when the brake lights come on the brain enters a stand-by mode and disengages the "cruise" (maintain constant speed) function and you start losing speed, to get back up to speed you need to let off the brake pedal AND hit the "resume" button and let the cruise control do its thing.
The vacuum switch on the other hand is a mechanical fail-safe that bypasses the electronic controls, if you press the brake pedal hard enough to trip the vacuum switch it will dump all vacuum from the cruise servo motor thus releasing the throttle arm on the IP and allowing it to return to idle. This will happen regardless of what the cruise brain box wants to do, if for whatever reason the brain box never received the "brakes-on" signal from the brake switch (for instance defective switch or wiring connector) then the moment you let off the pedal and vacuum builds up in the servo motor the cruise will instantly get up wide open throttle and accelerate till you're back to up to initial speed (unless in the mean time your speed dropped below 30mph in which case the electronics will enter stand-by mode automatically).
For the record newer trucks do not have a vacuum dump switch because their cruise actuators do not use vacuum and are all electric, said trucks now have a hydraulic pressure switch mounted on the master cylinder and it functions much like the vacuum dump switch on older trucks except vacuum switches don't leak fluid and catch on fire
So I would say that the two cruise wires that went to the clutch pedal will just get connected together, or do they work the opposite way?
The two wires are connected together when clutch pedal is in its up position, their contact is only broken when clutch pedal is pushed in. If the wires were permanently attached together without a clutch interlock switch then every time you clutched in to shift while your cruise was operating the cruise would try to redline the engine (whether it succeeds depends on how quick you are grabbing the next gear or hitting the cruise "off" switch
). The easiest way to bypass a clutch interlock switch on a '89-up (and possibly '88) truck is to hit the junkyard and find a truck of the same body style that is factory equipped with an auto trans - said truck will have a jumper connector plugged in the socket where the clutch interlock switch goes in your truck, the wiring between auto and manual trucks is identical except for what goes in that socket (clutch switch or jumper plug) and what goes on the very end of the harness (auto trans or manual). Since automatic transmission in general do not "neutral out" while shifting between gears there is no need to break contact like how the clutch switch does it. Alternatively you can cut the four wires and connect them red to red and green to green and it will do the same thing as the factory jumper.
I ordered a B&M floor shift unit for the new automatic that has a built in neutral safety switch and a reverse light switch. I'm thinking the other two wires on the clutch pedal for the starter, can be wired to the safety switch on the new floor shifter?
Actually on the C6 transmission both the neutral safety switch and the backup switch are integrated into one assembly that IIRC is bolted to the side of the transmission case itself and is actuated by the shaft coming out of the transmission. Same is true for E4ODs as well. There fore as long as you have the factory harness piece that goes between the transmission itself and the round green 8-wire connector dangling on the driver side inner fender there is no need at all to wire anything up to the B&M shifter itself. That is unless the B&M shift linkage requires removing of the factory switch from the side of the C6, then you're in for some fun rewiring the thing. Either way you should have the green wires at the clutch interlock switch connected to each other, or cruise will not work.
