cruise control fix

[bastianshaw]

Something astounding happened the other day, the CC on my 89 325is has been inop for YEARS... i checked:
both brake and clutch switches, and fuses, wiring.. still nothing

after installing a new head unit and shifter bushings I was driving down the street and thought"lets try it" to my utter amazement it worked. That night I went to go for a drive and noticed the check panel indicated a tail light out. I swapped it and went on my way....no more CC. They share a ground and whenever I remove the light I get CC w light no CC. I thought i would share this as it really would have helped me despite starting a thread specifically looking for this type of info.

Ill try sanding where the light goes into the bulb holder and that should fix it i hope.

Hope this help someone else

[jlevie]

Do not sand a bulb socket. That can remove the plating and result in rapid corrosion of the socket. Use nothing more abrasive that a brass bristled brush, like a shotgun bore brush, to polish the inside of the socket (all the taillight sockets probably need this). As an FYI, the ground point for the rear lights is behind the upper part of the rear seat. But the ground for the cruise control module is behind the dash. That ground might be iffy and the change of head unit might have affected it.

[bastianshaw]

Do not sand a bulb socket. That can remove the plating and result in rapid corrosion of the socket. Use nothing more abrasive that a brass bristled brush, like a shotgun bore brush, to polish the inside of the socket (all the taillight sockets probably need this). As an FYI, the ground point for the rear lights is behind the upper part of the rear seat. But the ground for the cruise control module is behind the dash. That ground might be iffy and the change of head unit might have affected it.

interesting news on the ground points as I pulled my rear parcel shelf for the first time as well..hmmmm

Jim, where exactly is the ground? I doubt thats it as I said the tail light seems to be the spinner here, although had it not gone out I never would have known and an intermittent ground would burn a bulb

[bastianshaw]

so i cant get my tail lights to stay on, i looked at the connections and they appear to be clean...no corrosion or carbon...id REALLY like to get my CC and tail lights functioning at the same time and consistently. Has anyone else had this same problem?

[jlevie]

The ground for the stuff in the rear of the car is behind the rear seat back.

The taillights have nothing directly to do with the Cruise Control.

[bastianshaw]

so all they have in common is a ground? thats it?

[Todd Black 88]

No, he is saying they don't even have a ground in common. The CC grounds under the dash, the brake lights ground under the upper part of the rear seat.

[bastianshaw]

No, he is saying they don't even have a ground in common. The CC grounds under the dash, the brake lights ground under the upper part of the rear seat.

like under the parcel shelf?
cuz I was banging that area w a sledge pretty hard recently

[jlevie]

The ground point is roughly half way between the rear seat pan and the parcel shelf.

[bastianshaw]

No, he is saying they don't even have a ground in common. The CC grounds under the dash, the brake lights ground under the upper part of the rear seat.

The bentley states that the required ground at pin 9 on the CC control unit comes from the brake light bulb

[bastianshaw]

The bentley states that the required ground at pin 9 on the CC control unit comes from the brake light bulb

is this irrelevent?

perhaps im not being clear, my RR tailight is now intermittent, like i can tap on the outside of the tail light and itll come back on, when the tail light is out the CC works when the bulb is lit it does not. What am I missing?