The Stovebolt Site Forums The Shop Area The Electrical Bay Brake light short to RH turn

Hi, I have an issue on my 66 c10. When i step on the brake, my RH turn indicator light comes on, the brake lights come on in the back as well as the RH front turn indicator. Where is the best place to start looking. My dad bought this truck new and it is all original, wiring harness, switches and there is no trailer plug or wire splicings.

Thanks,
Pat

Check your grounds.

Thanks, I will check grounds. Would a bad ground affect only this single circuit? Does the brake light circuit go thru the turn indicator cam?

Pat

When I ran maintenance shops, my mechs would come in and ask me "why doesn't this work right"... I ALWAYS said "go check the grounds"... they seldom came back!

Make sure it has the right bulb. The right bulb inserted correctly. And that there is not a filament, inside the current bulb, touching the other filament.

I just came through a similar struggle. Aftermarket light sockets came with bulbs. Nothing worked. Swapped to a different bulb and all problems resolved. My grounds were reaffirmed as first course. But as I went through the process I was looking for a list of the correct bulb numbers for the parking lights and for the tail Lights (1966). Does anyone have that list handy? Maybe helpful in this case.

I"ve got a list of applicable bulbs, somewhere, I'll have to do a couple of searches and see if I can find it.

here are a couple of lists. I have not found the one that I was looking for, yet>

Before I answer, I need to be sure what you said and additional questions.

1. When you step on the brake pedal, do the correct filaments on the brake lights come on?
2. You say the dash indicator light comes on. Does it flash or just stay on when brake pedal is depressed?
3. Do all fright and left turn signal lights flash as they should? Does the dash indicator flash as it should? Try this with brake on and with brake off.
4. Check as per glenns towing suggestions.
5. Report results/answers.

Wiggle the turn signal lever during the problem you mention and see if anything changes. Check the condition of the brake light bulbs and their sockets.
The brake lights, the turn signal lights, flasher and dash indicator are all routed and controlled thru the turn signal switch.

On a truck that supposedly has had no work done either in the past or recent, the common issues are ground (hard to find), bad bulb, corrosion, loose wires, turn signal switch.

Corrosion can be in the ground paths or the power paths. It can be located at screwed connections, solder connections, fuses, bulb sockets and connector contacts.
The answers to my questions are a start at troubleshooting and will result in the next steps from me and others. You will need, at a minimum, an ice pick style circuit checker.
Sometimes we tell posters to "check the grounds". That is much easier to say than do. There are dozens of places and many are hidden. Lets get a few answers first. It is true that more than 50% of the time it is a ground problem because there are almost no wires in the ground path. It's all "intimate contact".

Bartamos,

1. When brake is applied both rear brake lights AND the RH front turn light come on steady on the "bright" filaments.
2. When brake is applied the RH indicator lights up and stays on steady.
3. All turn signal lights work as they should with brake applied or not.
4. The turn indicator over rides the "brake issue" with both RH and LH brake and indicators working as normal when brake is engaged.
5. All lights and gauges work properly. Dash, interior, radio, headlights(high and low), high beam indicator, all park lights, turn and brake.
6. I will check bulbs tomorrow.

Thanks all!
Pat

A brake light bulb is sending power to the RH turn light.
1. It's two elements are fused. Visually inspect filaments with magnifying glass.
2. Loss of ground back there at the socket.
3. Voltage leak at socket/bulb.

Take one brake bulb out at a time to see if RH T/S light goes off. See which one makes it go off. Switch them. Do several of these test to be sure it's not both or that it's not them at all. If it's not the bulb, it is probably ground. Provide temp grounds to sockets with wire or screw driver tip, etc.

Since we haven't heard form you. you have probably found it already.

I swapped the front and rear lamps side to side. No change
pulled all bulbs and brake still activates the turn signal indicator

Im going into the turn light mechanism tomorrow.

Yes the turn signal switch is basically a router for those lamps you are having trouble with. All those circuits go thru it. Be sure to check the rear metal lamp sockets. That is the place that the bulb gets it's ground. Then the rest of the chassis to get back to battery negative post....eventually.

Found it! So I start into the turn indicator mechanism and when I went to get more wire slack from up under the dash, I see this splice wire running from the connector block to a wire headed out through the fire wall. I removed it and everything is good. Apparently at some point Dad or Gramps had an issue and tried a work around. Danged if I know what that was but everything works good now except the horn. Everything looks factory, the horn works when I supply direct power. How do I trouble shoot the horn relay?

Thanks,
Pat

So did you try the horn when that wire was hooked up and the turn signal on RIGHT? Maybe it worked then.

Don't know if that mystery wire was a horn wire, but here is the wiring for you to trace. Colors may not be accurate.

1. Black wire from horn trumpet to horn relay.
2. Red from horn relay to a good non switched battery positive source.
3. Dark Green wire from relay up thru column to horn mast bearing. (this wire probably goes thru the column connector which can be called the turn signal connector)

Your trouble can be either bad relay, missing wires or the horn button parts. obviously horn trumpet is grounded and works.
The green wire to button grounds the relay, closes it's contact which supplies the red power to the black trumpet wire.
The horn button usually pushes on a cupped/large belleville washer, that grounds the green wire to the column/wheel. you will see how that all works if you take it apart. this last issue should be easy to troubleshoot.

You can ground the relay terminal that the green wire attaches to. This will show if the relay is working and narrow the trouble.

Where did the mystery wire go after it went thru the firewall?

I pulled the horn relay and jumped to the battery and nothing. I opened the relay and the coil windings were burnt and the wire was burned off of the grounding post. A new one will be here in the morning.

The jumper was connected to the blue/purple wire on the far right in the pic of the turn indicator connector block and ran to the brown wire in the pic of wires running through the fire wall. On the engine side of the fire wall it is on in the upper group and it goes down and to the rear, I'm assuming tail lights.

Here is a few pics of the truck in question. My Dad bought it new in Sacramento CA about a month after I was born. Its nothing fancy as it was all white with one mirror, one visor, no rear bumper and all controls were as cheep as you could get. The only option was the V8 283. Dad said he couldn't see spending the extra $75 for the 327. My Gramps had it for quite awhile after my Dad sold it to him in 1969 to by a 67 ford station wagon after my second brother was born cuz we needed more. It came back to my Dad in 1988 when Gramps didnt need it any more and Dad had it re-painted, new wood bed installed and seat recovered. No rust ever and has original rubber floor mat and pedal covers. I rebuilt the carb and that is all. The cap, rotor, points, wires and all are from the late 70's. Spent most all its life in Ione CA. There is a spare set of points and condenser in the glove box with the receipt from 1977 along with a gas receipt for 29.6 cents a gallon.

Good times.

I believe the wire coming from the lower grommet should have been the reverse lights. Are those still working. Can you trace that wire down the driver side frame to the connection to reverse lights?
That's a nice looking truck and a great family story.

I enjoyed the story too. Nice looking truck and I like the stick in the floor. This is the same model my uncle had when I was little boy. My cousins and myself were riding down there long dirt driveway once. I thought I could do anything and they all dared me to do this. I stood on the tailgate facing forward and jumped off with my legs running. I hit the ground and rolled face forward ! Didn't do that again!
Glad you got the light problem fixed.

I enjoyed the reading too. I had my fathers 66 GMC for several years until Mrs. Rod nagged me in to letting it go. It lives on in Florida under the care of one of my Marines.

Check the ground wire at the steering column. May not be completing the circuit for the horn relay coil. I would ground the wire and see if the horn works. If it does the problem is probably the pin underneath the grounding spring is worn out or the wire is broken.