Brake Light and Horn not working

[Mike Szadaj]

One other thing, the horn relay must have a ground connection to the chassis. If you unbolt the relay and it is not touching the chassis it will not work. Sometimes after things are painted it is hard to get that ground connection. If the relay is clicking when the horn button is pushed that would indicate that you do indeed have a good ground connection.

 

[Nacho-RT74]

Horn relay doesn't need chassis ground because is triggered by ground from the steering wheel button. It can be floating around and will still work.

You can ground the prong coming from black wire on harness and will emulate the horn switch. That could tell you if the fail comes from cab or relay is damaged. Horns must be grounded thought. Violet wire handles positive from fuse box on post 70 cars because relay is down the dash frame but from alt stud on pre 69 being on radiator core support. Green wire with red trace is the positive output to horns.

Feed with positive the green wire will also bypass relay and will tell you the horn conditions.

Grounding the black wire at relay will make a click on relay. If clicks, relay SHOULD be ok and if horns don't work problem could be on horns itself. But since you already told got the horns working straight from batt ( is not wrong to make that ) it could be a wire failure?

With a test light you could check the prong coming out from green wire to check if gets voltage coming out from it when activating the relay.

Relay could be still clicking BUT failing the output to horns. Broken wire inside.

 

[Nacho-RT74]

Brakes. If you have hazzards, fuse should be ok, since brakes and hazzards use to share same fuse.

Brake pedal gets a switch with pink and white wires. You can jump them out and check if you get brakes. That will tell you pedal brake switch is damaged or not if brake lights lights up.

Next, should be the turning switch itself. White wire down the column ( turning switch harness ) which comes from pedal brake switch is Normally closed with rear lights, dark brown and dark green with turning lever in the middle. You can also jump out one or both of those wires with the white wire down the column. If rear lights come on giving brakes, fail is at turning switch. It could be in fact the cancelling cam asssembly which carries the contacts for brakes and turnings and is serviceable nowdays.