Power or grounding wire?

[iblackwe]

I have removed the original switch unfortunately and cut up the wire thinking I wouldn't want cruise control and now I am back tracking and trying to determine some properties of the switch.

I need to determine if the switch to "set, resume, and cancel" needs power or is just a grounding switch. If it needs power does the cruise control switch have to be routed through the (main box -5) needing to use the horn relay? I am thinking that it does because if the horn relay is triggered it might be powering something else along the lines of the cruise control system? If it doesn't can I just have it connected to an accessory 12v power supply?

Cruise Control.png
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Anyone that can provide help it would be much appreciated.

Thanks

[aquillen]

The cruise control switch gets +12V into the switch at B68-1 (RG). If you press "SET", it puts that +12V out B68-2 (LgB) to the cruise module at B94-10 (LgB). If you press "RESUME" it puts that +12V out B68-3 (RW) to the cruise module B94-9 (RW). If you press "CANCEL" it puts that +12V out to both B68-2 -and- B63-3 at the same time, by virtue of the two diodes incorporated into the switch assembly.

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For some reason Subary doesnt supply the +12V to the cruise directly from a fuse like usually done in most all the rest of the power distributions, instead...

The +12V is coming through the horn relay coil, since the other end of the coil is tied to the 12V horn circuit fuse. So if a person were "on the horn", this side of the circuit is grounded by the horn button, and you would not have +12V available to work the cruise control commands (ha) until you give up the honk. So either this was done to simplify some power routing, or they think a driver should not be allowed to honk and manipulate the cruise control at the same time (?) who does that (?).

I would expect that you could supply +12V directly to the switch, or an equivalent set of switches, from an accessory +12V. If someone else has done this already and can volunteer that it didn't aggravate the cruise module, connecting it directly to +12V would be the easiest of all.

Let's pretend no one knows if it is ok to run the cruise signals directly from +12, because Subaru is using the relay coil resistance to limit current into the cruise switch. Those relays measure 100 ohms. So to simulate that when running directly to an accessory +12V for your cruise switch power, put a 100ohm 1/2 Watt resistor in between the B68-1 (RG) and your +12V accessory power. Then I won't get in trouble for saying just connect it straight to +12V.

The switch doesn't use ground in any way.

If you are using some aftermarket/home brew switches, either have those diodes, oriented as shown, or you would have to have a cancel switch that has two sets of contacts that would but the +12V on both wires when pressed. (or - home brew - if you pressed both of your SET and RESUME switches at the same time - it would issue "cancel" request.

[iblackwe]

Thank you very much for the response and how much detail you provided, makes me much more confident in wiring this system. I will try to tap into the horn relay system to avoid any voltage surge although I also agree that it should not be an issue.

Thanks again!