Common Ground Stereo

[Nick]

When did Ford get rid of the common ground stereo in Mark VIIs? Was it with the replacement of the head unit from the rotary volume knob style to the flipper volume control?

[White'88LSC]

Nick, Do you mean they actually brought isolated grounds back from/to rear amps etc. to one common point to ground them all to avoid ground loops! I'm surprised and pleased. Does the factory manual show the location of that ground? I've got the toggle volume in both an '88 & '89 MK VII.
Were you saying they changed that at some point? Or whent to it? :confused:

[SQ_LSC]

Nick, do you have that system in your conti? If the 2 systems could be distinguished visually by the HU, That would be too easy. I'm hoping someone would know this for future reference. If you or anyone has a shop diagram of the older wiring system with color codes, I'd like to get a copy of the diagram for reference material for assisting others.

White'88LSC, What we have now is better at noise rejection then the system Nick is refering to. Hopefully he can verify this but commonly on older cars a 3-wire was used for a set of speakers vs. the 4 we use today. The ground was at the same location, just less wires in the harness.

[JoshMcMadMac]

I think that the Mark's stopped using that setup in 86, but I can not verify that. I think that Pro knows the answer, he is good with all the model year related stuff. I know that my 89 does NOT have a common ground setup, and I am 90% sure that the 88's are the same. There are a couple guys with 85's, Like Sick and Desert, that could tell us if they have that setup, and I know there is someone with a set of 86 manuals. We just need their help!

[Capt. Zilog]

If the amp is anything like the amp in my '94 Cougar, they eliminated the ground loop problem by making the amp run on 6v-12v, relative to the car's ground. Smart enough, but annoying as well.

[Desert Stallion]

Couldn't tell ya' much about my '86 because the previous owner had already ripped everything apart to install aftermarket stuff. My '85 had the 3 wire speakers though, but y'all already knew that.

[pro-five-oh]

I think 1987 was the last year for the common ground. It coincided with changeover to passive head units instead of ones with built-in amps. smile.gif

[White'88LSC]

Speaking of wiring and head units. Does the factory head unit contain amps for both front and rear, or does the HU just amp the fronts and line level (2volts rms) to the rear spkrs which I believe have their own amps? SQ?, anyone? :confused:

[JoshMcMadMac]

quote:Originally posted by White'88LSC:
Speaking of wiring and head units. Does the factory head unit contain amps for both front and rear, or does the HU just amp the fronts and line level (2volts rms) to the rear spkrs which I believe have their own amps? SQ?, anyone? :confused:

Depends on your stereo. Certain models had a "rear only" amp and on others the amp ran all four speakers. On the 88 (which I am assuming you have) I believe the amp ran all four speakers.

[Nick]

White'88LSC, Ford used common ground stereo for a period of time before switching from them to a setup you find in cars today. I am not sure what the wiring differences are exactly, but it was to my limited understanding that there was one single ground for the stereo system and the speakers had positive leads only. I don't recall seeing where the single ground for the stereo was. I would have to search through my EVTM manual. I believe the older, common ground stereos used the deck amp for the rear speakers and the head unit for the rest.

SQ_LSC, it has been my experience that the stereos with the rotary volume control with the black face are common ground systems. My '85 Continental and my '86 LSC both have common ground stereo systems (PITA if you want new speakers) and both have the same head unit. I also know the stock speakers in the cars have a 6 ohm resistance, which is marked on the magnets. Are the identical, but titanium-colored JBL head units with the rotary knob also common ground? I am going to have to find my EVTM manual to find the wiring diagram.

[serebin]

So did we establish that 1988 was the beginning of the end for the common ground system?

I'd like to know since I have a '88 and waiting on a HU to install as we speak.

Oh, and on systems that don't have a common ground, are the speakers 6 ohms as well?

[serebin]

I just wanted to make sure after reading this 1988 LSC stereo install (http://lsc.netherealm.net/stereo.html) because that author says the 1988 DOES have a common ground system, which is not what I have been reading here, or in other posts here.