brake light fuse blows when I turn on headlights

[Montana54]

I have a 1965 C10 long bed and need some help with wiring. When I pull out the headlight switch the headlights work but the brake light fuse blows?

[Montana54]

I have a beat up 65 c10 and when I pull out the headlights the brake light fuse blows. this is the last problem to work out before I can get it on the road.

Merged,
Please don't do this....

Copied from the rules:

XIV. Multiple Posting - It is simply not acceptable to post your question more than once, or to post it in more than one forum. Choose the forum that your question or post best fits in, and place it there and only there. If, after posting, you feel it should be in another forum, private message the forum Moderator and ask if they would move it for you.

[cdowns]

get under the truck

inspect the wire harness running down the frame rail on the drivers side for frayed wires and a shoirt circuit

[joe231]

double posting is against forum rules

are you sure it is the brake light fuse, and not the tail light fuse?

[Montana54]

Sorry about the double post.

the fuse says "brake" but when I put a fuse in, the brake lights and turn signals work but when I pull out the headlights that fuse blows and tail lights never come on.

[joe231]

i'm thinking maybe you have a bad headlight switch. do you have access to another one you could swap in to check?
you can use one from a truck up to '87, the newer ones won't light your front running lights without a wiring change, the tail/stop circuit is the same, so you could check it against the one in your '66

[tommys66]

Does the fuse blow when you hit your brakes? Does that circuit control the parking lights in the front? you could unplug each harness under the hood, one at a time checking to see if the problem is in front harness, or the rear. narrow it down to which harness is causing the problem then trace your wires from there. prolly just a nicked wire somewhere, the reason the fuse is blowing when you pull the headlight switch is that is when you are sending power to that circuit. Does any of this help?

[ChiefRocka]

In addition, does the fuse blow in both positions ? (parking light and headlight)

Pull switch completely out, then insert tail fuse. If it blows, then it's in the rear harness. If not, then it's in the front circuit.

The front markers only light in 'parking' mode.

[joe231]

this is a double post....cheif can you combine it with his post in the electrical forum?

http://67-72chevytrucks.com/vboard/s...91#post3035691

as far as i can tell from the diagram i have, the only thing the brake light circuit and the tail light circuit share is supplied power at the headlight switch, which leads me to believe, since the brake lights work properly with out the headlight switch on, that the headlight switch is suspect.

this is a '64, but ought to be pretty similar

[283 Man]

lots of great information on that post!great job Joe!!

[VetteVet]

IBLHM LOL.
We need to use a little logic here. The brake/tailight fuse powers both the taillights and the brake light circuits. The fuse is blowing when you pull the headlight switch switch on.
Does the fuse blow when the brakes are applied? If not then the problem is in the tailight
wiring.
The only thing that blows a fuse is putting too much current through it than it is rated for.
This can be caused by too much current draw or a short to ground. What I think you have is a short to ground in the tailight wire. This means the wire is touching the frame at some point between the light switch and the rear tailights. The most common places are underneath the drivers side rocker cover and under the truck along the frame as Cdowns mentioned. It was common on our trucks to splice a trailer harness into the truck harness along the frame at the rear and over time this caused a lot of the problems with the tail/brake lights. HTH VV

[joe231]

i do what i can
hope i'm right.....

[Montana54]

well again sorry about the double post, I am new here and I'll will post a little about my truck and me later, but for right now I checked the wires running back to the taillights and they were pretty messed up, so I ran new wires to the tail light harness(thanks to that diagram), this made the brake lights and turn signals brighter, but still same problem. So from what you guys said I think it must be the headlight switch, I had to stop working on it today because of the snow storm, (I am from MA) so tomorrow Ill try another switch and let you guys know how it goes. Thanks a lot for the help.

[joe231]

VetteVet,
what is IBLHM and HTH? acronyms drive me crazy, if it is worth saying, why not say it?



montana54,
i was just trying to get your threads merged to get the info all in one location, no harm done, now you know what not to do....... and WELCOME!

[68K20 x Drill]

Every time I have had this happen, its been an aftermarket radio installed without a good ground to its case.