1995 F-150 XLT 2WD 5.0

I recently changed all of the exterior incandescent bulbs to LEDs, and my cruise control quit working!

It actually quit after I swapped out the brake/tail and reverse lights.

Thinking it might be the interrupter switch on the brake master cylinder, I got a new switch and installed it, but the cruise control still doesn't work.

I'd sure hate to have to reinstall all of the bulbs to troubleshoot the problem, largely because I shouldn't need to, as it makes no sense that one would affect the other. I'm thinking this must be a coincidence.

I've looked at the fuses, and none of them are blown.

Going down the road, if I try to engage the cruise control, I can hear a faint click from under the dash.

Any ideas?

 

interrupted a ground somewhere along the path. not sure which/brand LED you have but many require a voltage/power board and installing them will change the loads and voltages on your existing wiring harness. - thereby breaking stuff. be sure to put the original interrupter in.

You will need a good digital multimeter and wiring diagram, else start backing them out and put the stock ones back in, one or two at a time.

 

Sylvania automotive 3157R red LEDs stop/tail lights, and 3156 reverse lights.

They all work as they should.
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I still don't see how the tail lights interfere with the operation of the cruise control...

 

Because the cruise control circuit will not activate if you have a brake light bulb that is out. And when you have LEDs that don't pull as much current thru the system as a halogen bulb, it makes the cruise think you have a bulb out. You have to add resistors to the brake light bulbs to get the cruise to work again. I had the EXACT same problem on my truck.

 

These are the resistors I got to fix the low current issue with LED bulbs:

 

Yep and the ones he didn't use he sent to me and they worked on my truck too

 

It doesn't take any special or specific resistor - anything that allows some current to flow will work. Like one incandescent in the CHMSL. On my F250, I just added a cube relay triggered by the normal brake light circuit. It doesn't do anything (yet) - it's just a resistor, which is enough for the cruise to work. Eventually, I'll probably rewire the trailer brake lights to the relay.

BTW
The cruise doesn't quit because 1 bulb is out - it quits only if ALL (3) brake filaments are out. The reason is that there's no path to ground for the cruise feed that senses voltage from the brake circuit. With all LEDs or with 3 burned bulbs, the voltage appears to be high, so the cruise thinks the brakes are on, which cancels cruise. It's exactly the way the clutch switch cancels cruise on stickshift trucks.