Cruise Control: Can Bulbs REALLY Affect Function??

[shertex]

In my reading on potential causes of cruise control failure, I've seen some scattered references to the importance of using ONLY OEM bulbs (Bosch or Osram) in the brake lamps. Allegedly, using the wrong bulb affects the grounding of the circuit and can/will cause the cruise control to malfunction.

Is this true?

I have some off-brand bulbs in my brake lights, so I thought I'd at least ask. In my case, however, the bulbs have been in there for several years while the cruise control problems are of recent vintage.

Thanks.

Completely untrue.

The wrong bulb CAN melt the taillight but it has no effect on the cruise control except that a burned out bulb will keep the cruise from working. What it does is bias a transistor. When the light is on it sees 12 volts, when its off it sees a low impedance resistive ground. If its a burned out bulb and sees an open and doesn't work at all.

The type and wattage of the bulb makes no difference of any kind to the cruise control.

EDIT: Several members have the 4 brake light mod (doubling the wattage) with working cruise control.

[dpetryk]

I agree!

[ImBroke]

Originally Posted by ForcedInduction

Several members have the 4 brake light mod (doubling the wattage) with working cruise control.

I'm one of those guys. Cruise works great.

[pawoSD]

Originally Posted by ForcedInduction

EDIT: Several members have the 4 brake light mod (doubling the wattage) with working cruise control.

My dad's SD has the 4 light mod + a LED 3rd light at the top too, and his cruise works fine.

My cruise doesn't work, but its due to a flaky cruise amp.

[bodyart27]

GDL explains bulbs and cruise control function very well...

http://gdl-online.com/bulb.html

[ImBroke]

Bookmarked that site, I had forgotten what it was called. Thanks.

[Shawn D.]

There's a flaw in logic when folks say "I have added bulbs and it works fine..." or something of the sort. Adding bulbs isn't relevant, but "subtracting" bulbs (as the cruise drain senses it) is a problem. If a bulb burns out or there is sufficient resistance due to corrosion (which can happen with cheapo bulbs), the drain will see a high condition and think the brake lights are on, thus preventing the cruise from engaging.

That was always known and stated many times.

[Shawn D.]

Originally Posted by ForcedInduction

That was always known...

Well, many folks apparently don't understand that, given the posts above that say the cruise works fine with more bulbs. The addition of bulbs isn't relevant to the original post and confuses the issue.

[going_postal]

Originally Posted by Shawn D.

There's a flaw in logic when folks say "I have added bulbs and it works fine..." or something of the sort. Adding bulbs isn't relevant, but "subtracting" bulbs (as the cruise drain senses it) is a problem. If a bulb burns out or there is sufficient resistance due to corrosion (which can happen with cheapo bulbs), the drain will see a high condition and think the brake lights are on, thus preventing the cruise from engaging.

"The drain will see a high condition and think the brake lights are on, thus preventing the cruise from engaging."

I do not understand, could you explain??
With the brake light switch open, there is nothing to see.Corrosion or not , it is not in the circuit.
Thanks in advance for your reply.

[Shawn D.]

Originally Posted by going_postal

"The drain will see a high condition and think the brake lights are on, thus preventing the cruise from engaging."

I do not understand, could you explain??
With the brake light switch open, there is nothing to see.Corrosion or not , it is not in the circuit.
Thanks in advance for your reply.

The cruise drain is connected to the circuit between the brake light switch and the brake light bulbs. Thus, it "sees" ground through the brake light bulbs. That ground goes away when the brake light switch is closed and the circuit goes high (call it positive if you like), causing the cruise to disengage. If there is corrosion in the circuit, there will be additional resistance in the circuit, and the current flowing from the cruise drain to ground will thus cause a high condition, like a voltage "clog," causing the cruise to disengage. In either case (brake lights applied or corrosion in the circuit), the current from the cruise drain is impeded to the point that the current drops below the level necessary to keep the cruise engaged.

[ImBroke]

Originally Posted by Shawn D.

Well, many folks apparently don't understand that, given the posts above that say the cruise works fine with more bulbs. The addition of bulbs isn't relevant to the original post and confuses the issue.

There should be no confusion about the issue, Forced said it and explained it in his first post in this thread. Burnt out brake light equals no cruise control. Nor does cheaper bulbs vice expensive bulbs. I was throwing the added bulbs in there because a lot of the posts about this issue are from people wanting to add bulbs. As an added bonus he got the GDL link.
Not trying to be nasty, so don't take it like that.

[going_postal]

Originally Posted by Shawn D.

The cruise drain is connected to the circuit between the brake light switch and the brake light bulbs. Thus, it "sees" ground through the brake light bulbs. That ground goes away when the brake light switch is closed and the circuit goes high (call it positive if you like), causing the cruise to disengage. If there is corrosion in the circuit, there will be additional resistance in the circuit, and the current flowing from the cruise drain to ground will thus cause a high condition, like a voltage "clog," causing the cruise to disengage. In either case (brake lights applied or corrosion in the circuit), the current from the cruise drain is impeded to the point that the current drops below the level necessary to keep the cruise engaged.

Thank you Shawn D.

I had not looked at a wire diagram (lazy me)
Your explaination was clear and simple.
Thanks again

[Shawn D.]

Originally Posted by going_postal

Thank you Shawn D.

You're welcome.