Bizarre Electrical Problem - Looking for possible causes

[SomeoneStrange]

Hello! This is my first time posting, I was hoping I could get some advice on a slew of bizarre electrical problems that have popped up in my 9C1. Here's a list of everything that's going on:

1. Every so often, the taillights and reverse lights begin to flash in an alternating pattern rapidly, as if there were an active light rack on top of the car. They continue to flash even when the car is off! The only fix I've found is to disconnect the battery for a few hours so the system resets.

2. When #1 happens, the stereo in my car mutes itself and a prompt showing "Voice In" appears on the display. Lately, this has been happening every few minutes without the lights behaving weirdly.

3. I've noticed the sound of a relay in the driver's side floor panel tripping intermittently while driving - the relay also seems to trip whenever the brakes are pressed.

4. Similar to #3, if the vehicle is in park and the brakes are pressed, a large relay in the center console can be heard tripping.

All of these problems are intermittent, and sometimes difficult to repeat, which has stopped most mechanics from being able to find the issue. Can anyone think of a part I should be looking to inspect/replace? I'm more than happy to tear into the problem myself, but I'm not sure what I need to look for.

Thanks in advance!

[9C1fanatic]

Was your car formerly used by a police depart or other emergency services agency prior to your purchase of it?

Your car may be equipped with a factory option that flashes the brake lights and reverse lights alternately using the BCM Body Control Module. I would first start checking the GM police vehicle upfitter harness (should be under the center of the dash or passenger side. Look on the internet for the Caprice upfitters guide for whatever year model you Caprice is. Find the color wire in the harness that activates the tail light flasher.

I would bet that most or all of your issues are related to a poorly performed decommission of the car. Many aftermarket circuits may have been left partially intact causing issues such as this or with the brake pedal switch and or neutral safety switch. Many agencies install brake light cut offs, and install other equipment that is designed to activate/deactivate when the brake pedal is pushed or the vehicle is put into park. Usually relays are needed to make these functions work properly. You need to locate the up fitter harness, ignition feeds, and the battery power connection points in the trunk and in the upfitter harness to insure all customer added wiring has been disconnected. If you still have problems with the lights, I would then suspect the BCM being faulty as it can become damaged if certain circuits are allowed to ground out or in some case have 12VDC applied to them instead of ground.

[SomeoneStrange]

Thank you so much for the tip! I'll look everything up and crack her open as soon as I get a chance!

When I got the car, it only had 7,900 miles on it, but I suppose its possible that they installed and removed equipment in that time.

[Pursuit]

There is a wire that is a circuit that is from the BCM within the factory installed harness. When it is applied to ground it will tell the BCM to alternanately flash the tailights and reverse lights. Circuit 6841 D-BU/YE. EDIT: depending on the MY could be Circuit 6841 BU/GN. Could be occaisionally be grounding to bare metal.

Good Luck!

Maurice

[SomeoneStrange]

I suppose it would have been useful to mention that my 9C1 is a 2011 model. I should have some time to work on it over the weekend - I'll be sure to post the results here afterwards!

[bsparks72]

The files section can help you, at least with the flashing taillights. http://newcaprice.com/files.htm" onclick="window.open(this.href);return false;

Download the 2011 technical manual. Look on page 15. If it were me, I'd just unplug the flasher under the hood. If you pop the hood and look at the top of the passenger side headlight, it's just above that. There should be a plug in and a plug out of the little black box. Unplug each of those, and I think you have to plug them into each other.

"This option provides a flashing module, headlamp alternate high beam flashing, rear
alternate flashing of the stop and backup lamps and a control wire for connection a
customer furnished ON/OFF switch. A second control wire permits optional separate
control of headlamp flashing and rear lamps flashing via customer switching.
The headlamp flashing module is located at the right side of the underhood electrical
center. The headlamp flashing module is activated by application of 12-volts to a dark
green/red wire coiled in the right front footwell. When activated, the left and right
high beams and the high beam instrument cluster telltale will flash alternately at 2.4
flashes per second.
During daylight conditions, the Daytime Running Lights (DRL) are automatically
deactivated whenever the headlamp flasher module is activated; during nighttime
conditions, the low beams are automatically on while the high beams flash (unless
option VVS is present). Activating the high beam switch will override the flashing
mode and the high beams will operate continuously.
A 15-amp fuse (F16) protects the front flasher circuit and is located in the engine
wiring harness junction block at the right side of the engine compartment.
TAIL LAmps and backup lamps
When the headlamp flashing module is activated the body control module will cause
the left and right stop lamps to flash alternately with the backup lamps at a rate of
2.4 flashes per second. The center high-mounted stoplamp does NOT flash and
operates only with application of the service brakes. During nighttime conditions, the
tail lamps are automatically ON (unless option VVS is present).
Activation of the headlamp and rear lamp flashing can be separated. Call Kerr
Industries at 905-725-6561 for instructions."

[K9Vic]

Is your Caprice silver?

You likely have a factory dealer demonstrator and the removal of the equipment was done poorly. What bsparks72 noted may be the issue with the flasher module.

[elc32955]

On your #4 issue, there is a safety lockout on the shifter that keeps you from putting the car in-gear unless your foot is on the brake. The lockout disables when your foot goes on the brake in Park mode to enable shifting the car. I'm betting that's what you're hearing, and if so that's a normal condition.

Also... if your car had equipment de-installed, the devil is always in the details. Check your wiring & harnesses for a short to ground through a harness grounding through a nick in the insulation (yes, had that happen on a Dodge Diplomat before and it was a BEAR to find!). Also check the condition of ALL of your grounds that you can access. Yes, I've seen people unbolt a ganged ground bus to take out one ground wire, then put the bolt/screw holding the remainder of the entire bus together finger-tight. Looks like a ground, smells like a ground, but BZZZZZZZ..... wrong answer. Just a placebo so the de-install tech gets paid for his hours.

Good luck!
Eric

[9C1fanatic]

The flasher under the hood only is used to flash the high beam headlights. The brake lights and reverse lights are flashed by the Body Control Module.

[Tom Slick]

Actually, the factory installed flasher module controls the high beams, and the tail/reverse lights.

It can be set-up to run them all together on the same switch, or you can split them. (high beams & tail/reverse lights on separate switches)

Later,
Tom Slick