brake lights on

[my40ford]

40 ford deluxe is 12v. Have a new mechanical brake light switch but isnt wired in at the moment. When i turn the lights on the brake lights stay on, they actually come on soon as i hook the battery up. When i wire the switch in and change wires etc it still will not work correctly. Was frustrated before starting so what simple thing have i done wrong?

[cas3]

confusing question, needs about 4 answers. so new switch not attached, if old switch is attached, its not returning to off position. if you unhooked the old switch an did not finish the job, the wires are touching and making a circuit. if the old switch is hydraulic, the master cyl may not be returning to the end of its stroke and leaving pressure in the system. if you have a rotten wire harness the two brake light wires may be touching some where in that area. you're lucky the brake lights are wired to only come on with the key or the next problem would be a dead battery. they are usually wired to be hot all the time

[my40ford]

the car has a mustang mc because of the disc brake upgrade. i bought a mechanical switch that can be easily adjusted. i hooked that up to try things first with no luck. i disconnected those 2 wires and left them alone to see what it would do and the brake lights were staying on. I was trying to see if i was missing something down the line because of the 12v upgrade. im gonna try more diagnosing tomorrow if i get a chance

[JSeery]

Any turn signals involved?

[drolston]

Ditto the turn signal question, because the turn signals flash the brake lights. The brake light switch goes to the turn signal, them separate wires go through the turn signal to each rear brake light, versus the original wiring taking one wire from the brake light switch to both brake lights.

[51woodie]

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This drawing may help with troubleshooting you lighting problem.

[my40ford]

no turn signals

[JSeery]

Without turn signals the brakes are very straight forward, it is a single wire from the light switch connection to the brake light switch and back to the left tail light. If there is a right tail light, it is jumpered over from the left. Only thing I can think of that would keep the brake light on is a defective brake switch or a short across from the other wires in the harness between the brake switch and the tail light (or shorted across in the tail light itself).

[TJ]

Do you have a old harness, new harness, or something that has been patched together? If you have brake lights with the switch disconnected you have a constant hot going to the brake lights.

[my40ford]

yes I tested the wire going towards the rear and it is hot.

[JSeery]

It should be "hot" all the time to the brake switch, but if the switch is disconnected and the ends are not touching, then something is either wired incorrectly or there is a short to a hot wire in the wiring between the brake switch and the tail light.

[my40ford]

I have found out that the wiring harness i ordered had 2 wires that were not correct. it took me longer than i wanted to figure that out but my switch is wired in and all is working correctly...Thank you all again for the help

[JSeery]

Great work!