'99 S70 -- SC-901 Hook-up question

Post by **E Showell** » 21 Jul 2015, 04:23

I know Jim will be along any minute to chastise me for not posting this in the "audio" forum (we kid you because we love you Jim . . . ), but --

I'm well into an SC-901 upgrade. The car is a base model with SC-816 originally, so no underseat amp or harness. No big deal really. With some help I've gotten through discussions and searches regarding the wiring harness and how everything fits together -- and we have conclusive proof that it is well-nigh idiot proof if I can do it -- I've managed to get most everything where it should be, but here's the thing. There are two black plastic rectangular plugs that feed into the back of the head unit. I have the one on the left (the larger plug) squared away.

The one on the right is puzzling me. The harness I received appears not to have included the smaller black plug. Instead, I have a single yellow wire with a black trace in it with a clipped end. That single wire is supposed to be the only wire feeding into the smaller black plug.

Being the rebel that I am, I figured I'd just power everything up without the yellow-black wire connected and see what happened. Well, I'm still here and neither the car nor the head unit spontaneously combusted. In fact, the radio seems to play fine and all speakers, amp and Dolby unit seem to be working. I am getting a slight tic-tic-tic when playing CDs but I assume that is from the laser lens needing a good cleaning.

Can anybody shed any light on the function of the yellow-black wire and provide insight as to whether it is OK to operate the stereo without it being connected provided I cap off the wire?

I appreciate all assistance -- and no, I didn't post in the audio forum since that appears to receive almost no traffic.

Post by **BEJinFbk** » 21 Jul 2015, 08:38

It's the speed signal wire.
It provides info to the auto
volume control feature.

Post by **E Showell** » 21 Jul 2015, 09:00

Thanks much BEJ!

mika · Post by **mika** » 21 Jul 2015, 13:12

I had this same issue recently and also noticed there was an extra wire. We are both all set to go.

One time, I was rewiring a 240 radio and I plugged the new donor radio in, after soldering some new LEDs into the backlight for the radio...and it started cooking! So much gross smelling plastic smoke. I was coasting in neutral down a hill and boy did the neighbors see an interesting scene with my trying to unplug the radio while the car was off but still in neutral coasting.

Post by **E Showell** » 21 Jul 2015, 13:22

Oh man, you mean you let the smoke out -- guaranteed fail for electrical components.

mika · Post by **mika** » 21 Jul 2015, 13:24

Actually, the radio still worked after this.