Mechanics

CRUISE CONTROL WON'T WORK WITH HEADLIGHTS OR RUNNING LIGHTS ON.

1998 Ford Mustang • 183,000 miles

Cruise works if headlight switch is left OFF. Cruise WON'T work if lights are ON. Cruise QUITS if it is engaged then lights are turned ON.

HELP!

I need my cruise control after dark!

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Je Ce
April 12, 2013.




Check to see if your multifunction switch is working it may have a bare wire in steering column and grounding out. Also check the fuse in eng compt that is for drl/horn/fog lights. You may also have a bad clock spring in the steering column. The switch can be checked for resistance. The ground for that circuit is in right kick panel so check that for corrosion/rust.
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Hmac300
Apr 12, 2013.
NONE of those apply. All have been checked and all show good or as designed and manufactured and installed.

Tiny
Je Ce
Apr 12, 2013.
Is there a capacitance component to the system working or not?

Tiny
Je Ce
Apr 12, 2013.
If everything has been checked and working then the only thing I can think of is a loose ground from battry to body or engine to body, etc. If the ohms are correct from the switch then it has to be a ground problem. Check left and right front of engine compt for rust/corrosion/dirty and behind dash at right kick panel and finally near left headlamp breakout. There is also a ground at central dash but I dont'think this would be the cause. If this car has been wrecked and a body shop has repaired it then look where car was wrecked for wires not connected/ poorly twisted together etc. Most body shops dont' do a good repair job of wiring etc and will work for a little while

Hmac300
Apr 13, 2013.
Thanks. Never wrecked, but I will recheck all the points you mention and if I find anything I'll get back to you.

Tiny
Je Ce
Apr 13, 2013.
Checked, cleaned all ground strap locations in the engine compartment, cab and trunk I could find as you suggested and put colloidal contact grease (penetrox) for electronic/electrical contacts to make sure and made no difference.

So I'm bumfuzzled and give up unless anyone else comes up with something.

Why would it work perfectly with the light switch in the OFF position but not when the lights are turned ON?

Thanks anyway,

Je

Tiny
Je Ce
Apr 15, 2013.
The only thing I can think of is the module is screwed up but that would need scanning to see but you 've said everything was checked and is ok. The only other thing that I cold think of is a weak battery or low charging from alternator, when the headlights are on mor juice is required and takes away from the cruise. Or the belt and tensioner are worn and kinda doing the same. Belts and tensioner shold be replaced every 60k

Hmac300
Apr 15, 2013.
Thanks,

Brand new battery, was getting weak and went dead when I left the interior lights on overnight so changed it and tested everything charge related, alternator checked and proven good No codes thrown, have a reader but no way to scan the cruise module. And for it to work perfectly as long as the light switch is NOT turned/pulled on, I'm out of ideas. Next is to take it to an automotive electrical specialist and see what he finds/thinks.

Tempted to get a breakout box and test every wire/circuit. Too hard to get into those positions at 70 years old and body-parts broken several times.

Thanks for your input.

Tiny
Je Ce
Apr 15, 2013.
Just for future reference, I gave up, went around and changed every exterior bulb and the problem cleared up.

I found that Ford designed the ECU to disable the cruise if it detected any perceived defect with any brake or tail bulb and even though they all worked one must have had a high resistance or whatever and now new bulbs have cured the problem.

I just LOVE Detroit!

Thanks for you input and you can close this thread or use it as you wish, I'm done and gone.

Je Ce

Tiny
Je Ce
Apr 17, 2013.
Thanks for the update.

Hmac300
Apr 18, 2013.

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