Wednesday, August 27, 2014

Help! Vehicle electrical problems

I could really use some diagnostic help in determining what's going on with my 2005 Ford F-150 XL truck.  I've got three intermittent problems that I think are all related.

1.  For several months now, the cruise control will occasionally cut out in the middle of a drive with no warning.  It won't allow me to switch it back on, either.  Sometimes this is accompanied by a sort of crackling sound from the steering column, as if there were an electrical short-circuit, but sometimes not.  There's no smell of burning or any other electrical problem.  If I stop the car, turn off the engine, wait a few seconds, and turn it on again, everything works as normal.  The fault is intermittent:  nothing might happen for several trips, then for two or three in a row it will reveal itself, then it'll go away again for a while.

2.  For about six to seven weeks, I've had an intermittent problem with the air-conditioning.  While driving, it'll suddenly shut down completely - compressor and fan together.  If I do nothing, after one to two minutes it'll come back on again.  If I thump the dash just next to or below the fan switch, it'll usually come on again at once.  Like (1), the problem comes and goes.

3.  Over the past week, on three separate occasions when I've switched off the truck, the brake lights have continued to burn.  On two occasions I only noticed them when I came back to the truck;  on the third, I was looking for the problem, and noticed it at once.  If I restart the truck, wait a moment, then switch it off again, the brake lights go out again as usual.

I'm convinced these problems must somehow be related.  A dealer agrees that (1) and (3) are probably related, because (their service staff say) the brakes has to disconnect the cruise control when they're applied;  so if a single switch in that circuit is faulty, it might be the cause of both problems.  However, they can't see how (2) is related to the other issues.  What's more, they claim they can't diagnose the problem unless the faults occur while they're driving the vehicle;  and given that they're intermittent problems, there's no guarantee they can reproduce any or all of them.  They're willing to try, but I'll have to cover labor costs, so I might end up paying several hundred dollars without finding a fix at all.

I've had suggestions from a couple of mechanics that since the truck's now a decade old, it might be a good idea to retire it and buy a replacement;  but have you seen the price of trucks these days?  It's ridiculous!  I've thought of buying a used truck as a replacement, but I've only driven 60,000 miles in mine, and all the used trucks I've seen in the 5-6 year old bracket will cost me mine as a trade-in plus at least $10,000 in cash for a vehicle that's already covered many more miles than mine has.  I could look at replacing it with a fuel-efficient small vehicle to run errands around town, reserving the truck for longer trips or hauling things;  but then we'd have a third vehicle to look after, insure, etc. - all additional expenses, and on our limited budget, I'd rather not incur them.  One mechanic has suggested replacing the entire wiring harness in the cab, on the principle that it's probably going to solve the problem even if we can't identify what the problem is!  It'll cost a lot (probably into four figures), but in the absence of certainty over specific circuits, he reckons it's the most likely 'cure' for what ails the truck.

Frankly, I'm at a loss what to do next.  I don't want to drop several hundred dollars on a dealer investigation that might not find the problem;  but I can't carry on driving a truck that might develop worse problems over time, and strand me at the side of the road.  I also really don't want to spend a couple of thousand on a complete wiring harness replacement in the cab.  Can anyone offer helpful (and practical!) alternatives?  I'll be very grateful.

Thanks in advance.



Anonymous said...

On my vehicle (Ford) it was a bad ground from the dash to the truck body. There are probably 2 or more grounds That you can see if you are upside down standing on your head, and there are probably others. With the crackling in the steering column could also be a bad ground. Good luck intermittents are hard to find.

Murphy's Law said...

Re: Price of used trucks. I've been looking to, but that stupid "Cash for clunkers" program pretty much wiped out the used truck market. It'll likely take a while before there are that many beaters in the market to start pulling truck prices down again.

og said...

The brake light problem is the cruise control problem. You have an out of adjustment/failing brake light switch. the cruise goes off because the brakes are on, it won't leave the cruise on while the car is being braked.

the switch is not particularly expensive but if you look at it you will see what causes the problem- it's a little rotary actuator and it comes out of alignment. here's a guy who fixed his with a piece of electrical tape.

Common problem, simple resolution, opportunity for the stealership to make the payment on their new welder.

Paul said...

I would vote Og's solution.

It is an intermittent problem where they all intersect. Could also be something around the block all the connections in the dash use to get outside the dash. Check that ground and some of the problem should be resolved.

I would get rid of the truck and move up some years if I had the cash. YMMV.

Rev. Paul said...

Yep, what Og said.

Anonymous said...

I didn't know Ford bought Lucas Electronics. When did that happen?


Jesse in DC said...

There is or was a recall on the cruise control switch. Check that out, as it burned some garages down. That might affect the brake lights too, but no idea on the AC.BTW, if there was a recall, recalls are forever. The law states there will be a repair...

R said...

Does your local public library subscribe to AllData or something similar that you could use for research. If you can access decent schematics you might be able to figure out an easy diy solution or verify that there is a recall.

Anonymous said...

Rock Auto has the brake light switch for $28.79 plus shipping.[ID]=0&ck[idlist]=0&ck[viewcurrency]=USD&ck[PHP_SESSION_ID]=kt7n01a2ckdc3776430cmn8dr3
Like og says, I'd replace that first. If it doesn't fix the problem, then I'd rig up a voltmeter between the hot side of the brake switch and ground and leave it hooked up while driving. Use gaffer's tape to attach it somewhere in the cab where you can see it. It will normally read somewhere around 12 Volts. If when the problem occurs its reading drops to near zero, then you have a short to ground somewhere in the circuit. Most likely, however, it's the switch. As far as the AC is concerned, it's a different circuit altogether, and the problem may be one of several switches or relays, though it's probably not anything more serious. I'd just wait for it to fail altogether and then try to diagnose the problem. In the meantime, check whether there is proper air flow though the evaporator core (If its blocked you won't be getting much air out of the vents). If this or, less likely, air flow through condenser (located in front of the radiator) is blocked, then the freon pressures in the system are not right and the system will often shut down as a result.

Well Seasoned Fool said...

All good comments, especially the brake light activator switch. Bad grounds can be overcome by making new ones. Use a heavy wire, and a couple of terminals. Find bare metal on the dash, drill a small hole,and attach the wire. Do the same on the frame (or bare metal on a unibody). You may need to scrape off paint. Doesn't hurt to do two or three.

While not applicable here, in thirty years of selling used cars, I found the majority of electrical problems went away with the installation of a new battery, and new battery cables.

Able said...

See! You should have bought British - one of those nice MGB's with that 'failure proof' Lucas electrics instead.

P.s. What's 'cruise control'?

Ducking and covering and searching for cover as I type ;-)

Sevesteen said...

Googling to try to verify my theory I found that the brakes go through the Multifunction Switch (turn signal switch) and that these are relatively common failures on Fords, and would account for the brake lights and cruise.

The theory I was trying to verify-I seem to recall that in some vehicles the brake pedal switch supplies a ground rather than 12v. If that's the case, I'd suspect that the cruise also uses this ground to turn off. If the insulation on the wire from cruise to brake switch was damaged it could cause similar symptoms--providing the rest of the path to turn on the lights and shut off the cruise.

A cheap digital multimeter would greatly assist troubleshooting. Harbor Freight usually has them for around $5 or so.

Peter said...

@Able: If you're not careful, I'm going to sic Brigid and Partner in Grime on to you . . .


Anonymous said...

For intermittent problems I prefer an analog multimeter. It seems to be easier to notice, and be sure of, the motion of the needle than the flicker of a digit. If the intermittent happens between samples on the digital meter, you can't see it, but the analog needle will bounce. How big a bounce depends on the damping of the meter.

My opinion, based on ~60 years experience. YMMV.


Miguel said...

I had something similar with my Explorer Sportstrack and it was what Sevesteen said: Multiswitch.
You will need the part and dismantle around the steering column to replace. I am not that good so it went to the shop & almost $600 were gone.

MSgt B said...

Rule #1 - In order to troubleshoot the problem, you have to duplicate the problem.

I hated stuff like this back when I worked aircraft. A flying aircraft generates a lot of vibration, but on the ground, whatever problem the pilot reported has gone away.

Problems like this would haunt us for weeks before it got bad enough we could track it after landing.

ASM826 said...

I would start with the brake light switch, the one that opens when the pedal is depressed. Just replace it and make sure it is adjusted to not open until the pedal moves more than a 1/16 of an inch. That way road vibration won't be enough to make it flutter. Any other switch that the signal has to pass through is also suspect.

I would follow that up with testing the ground on the dash and steering column. I would do this by running external wires. Make a new ground wire that runs from the chassis to the dash and another that runs from the dash to the steering column. .

Do one thing at a time and drive in between until you find the source

KurtP said...

Like someone said once at work when we were having trouble with a truck...

It's probably that Blue oval on the front grill :-D

Mrs. S. said...

Og's suggestions sounds like a good place to start. Also, don't forget to clean your battery contacts while you are at it.

Merlin said...

Also, to see if your brake light and cruise control disconnect switches are just mis-adjusted a bit, when the cruise control cuts off, try lifting the brake pedal by putting your foot behind it, and lifting toward you. If the switch is just too close to being opened, lifting the pedal will close the switch, and allow the cruise control to operate.

Anonymous said...

No clue on the electrical components of automobiles, you need a witchdoctor to figure those out. :^)

Definitely agree on the trade in dilemma. My GMC is 14 years old and has 154,000 miles but still has miles to go before it goes to pasture (I think). It seems that many new vehicles (even right off the lot!) have issues of their own. I remember when you bought new to avoid problems - now its a possiblity you are buying new problems with even higher price tags.

Joe in PNG said...

#1- get a Haynes manual for your truck- if you don't have one already.
#2- as already mentioned, fix the known problem, then see if that fixes the others
#3- if in doubt, it's probably a ground
#4- it may be the multi switch. A steering wheel puller is cheaper than a mechanic's visit.

Finally, if all else fails, go to a auto electric specialist

Anonymous said...

The AC could be related to the brake switch problem due to the fact the computer needs a clean rpm reading before allowing the AC to run. If you are unable to do the repair yourself, please take to the shop soon because you may be driving with your brake lights on and people following wouldn't know when you really apply them.

Anonymous said...

Og said the same thing I was thinking when I read your post. The A/C, I have no clue; then again, that's a convenience issue, not safety.
Mike, I (former Navy AX, & still chasing trons 30 years later) agree. Analog meter needles will twitch, at least, whereas the DMM won't catch quick transients. They're good for checking the integrity of (discharged, of course) caps, as well: resistance setting, hit the leads, watch the needle climb. Discharge, reverse leads, watch the same. The voltage produced by the meter charges the cap. Trick I learned lo these many years ago. Bless the Simpson 260!
--Tennessee Budd

Anonymous said...

Find a good auto electrician who works on that make.
not a mechanic-that's just off the replies you got when you asked mechanics..
sounds like the guys are on to it, bad switch, bad earth or bad wiring connection.
Check the switches are actually faulty before replacing if possible.
i know its obvious but a lot don't do this.

Anonymous said...


I'm not a car guy, so I posted your question to some friends of mine who definately are. Here is what one of them said: Okay, not being "Ford" trained let me start out saying that I agree with the dealership on the Cruise Control/ Brake Light thing. Best I know, the Brake Light Switch (mounted usually on the pedal - below the dash) is the common link here. It is used to cancel the Cruise and operate the brake lights. You should be able to replace it yourself. Go to "O' Riley's or Auto Works and they should have an "After-market" switch that would work and be able to show you how to do it.

As for the "crackling" sound that you hear from the steering column, do you hear it on turns only or "more often" on turns? I have had some of that in other vehicles of that era. There is a "reel" in the column used on the Air-Bag Restraint. It works like a Tape-Measure. Extending and retracting on turns and sometimes making "crackling" noise. I had a 2006 GMC pickup with the same problem. Needs lube.

The HVAC Fan problem could be TWO problems but that depends on a lot of things. Or it could be that you have ONE problem and it appears that you have two. First, if you can swat the dash/control head for the HVAC, and temporarily fix it, most probably the switch or control head itself is bad. Some of them have a separate fan (speed) switch, some are modules with the fan controls being part of a printed circuit or mini-controller. I can't tell you what is used without looking at a manual.

As for the compressor being "shut-down" with the fan, how do you know that the compressor is "stopped" along with the blower fan? Almost all manufacturers use a "cycling" system in their AC systems that allows the compressor to stop running (clutch disengage) to keep the system from freezing up. Those that don't have some sort of valve (Commonly called a Thermal Expansion Valve or TXV) that controls system pressure by temperature to do the same job. If the compressor is in its' "off " mode it will appear that it is NOT running when in actuality is in "pause". As soon as the system pressure drops to a point, the compressor comes back on and raises the pressure in the system. All AC systems use something in this area. Have you ever had the AC system serviced? Does it feel cold when it is on (even on a hot, muggy day?). The outlet nearest to the AC unit (RH side of the cab) should register 40 degrees or so with the fan on "high" on a warm/hot day. Anything greater than 50 degrees would require service (recharge). You said that the compressor would return after 2 minutes of down time. This could be nothing more than a long cycle time that says the system needs service. If the system freezes - it takes two minutes to thaw and come back on.

I hope I helped!

Will said...

if you do pull the steering wheel to access that internal switch, be careful to not disturb the grease on the horn track and the contacts that ride on it. If you wipe that off, good luck trying to find a replacement!

clark myers said...

I hope your issue has been solved by now. My older vehicle experience may not apply to your truck.

On my truck which is an earlier model there is a mechanical switch off the pedal which works the brake lights. There is a hydraulic switch off the master cylinder (which as designed leaked brake fluid all over the cruise control brain box hence a recall as mentioned) which tells the car brain but not the brake lights that the brakes are on and the cruise control trips off to a reset.

The switch off the master cylinder also told the car the brakes were on for a start the car safety interlock.

What is called a "tape measure spring" is commonly called a "clock spring" a long coil that coils up and uncoils as the wheel is turned to pass a feed from the fixed column to a turning steering wheel with the horn and cruise control switches in the steering wheel usually behind an airbag - a specific procedure is absolutely necessary to remove (and replace) the airbag safely to access the steering wheel parts. See Dr. Pournelle over the years for a contact improver called Stabilant (aka Tweek in the hi-fi business) which has solved a lot of issues and is commonly used on off road and racing vehicles where vibration and dust degrade contacts.

Things to check - brake pedal travel to stop is too much (pads worn takes a lot of brake fluid to fill in behind the caliper pistons check for low fluid at any point) and the pedal is not retracting all the way and so completing the brake light circuit and/or gunk in the master cylinder/booster system that is keeping the pressure up sometimes the master cylinder piston forward or applied just a tad and so the brake pedal is hanging down for the mechanical switch while the hydraulic switch is kicking off the cruise control and maybe the clock spring has wound up and wound down too many times for a bad connection. Can look for brake pedal travel with the engine off vacuum exhausted by repeated applications compared to then turning the engine on creating a vacuum and drawing the pedal down just slightly and such.

But maybe not. In any event there are F150 specific sites on the web worth searching and posting on for specific information on your specific model and year.

The AC is typically a mechanical switch issue as the switches are worn with much turning giving bad contacts. On the other hand some AC is set to cut out on acceleration and come back later. Check at least the sight glass for coolant and the output temperature as mentioned when it is working.

clark myers said...

Quoting Dr. Pournelle on Stabilant
" I used some Stabilant 22 on all the cables. I’ve been writing about Stabilant 22 since S-100 says, and it has won my Users’ Choice award more than once. They sent me a supply of the stuff a dozen years ago, and I still have some left. It is a contact enhancer, and will often fix mysterious problems – one of my early Pournelle’s Laws was that 90% of computer problems were with cables"