Before I post for reply I want to thank the FTE for this site and anyone who offers help for myself and others. It is much appreciated.

Preface: '73 Ford F-100 lwb, 390, second owner.

My brake lights went out. Tried to replace the fuse but it blows as soon as I try to put it in. Checked all the usual things:
brake pedal switch: GOOD, power to fuse (slot?), power in (one side) and no power out (other side): GOOD,
turn signals: WORKING,
flashers: DON'T work.
Checked flasher plug(?) and it is good.
When the fuse blows for brake and hazards (1 fuse, 20 amp) my dome light blinks dim at the same time.
Disturbing: I have no fuse at all in my slot for "ins panel" but my dash lights work fine.
Help. Please.

 

To keep from blowing fuses, connect a test light across the fuse that keeps blowing. Or rig up another bulb so you can use your test light elsewhere. When the light is lit, it's telling you that there is a draw on that circuit. If everything is off that's supposed to be off, the bulb being lit indicates a short circuit. There's still enough power supplied to the circuit through the bulb to trace down a short but it will save on fuses.
Hope this helps.

 

Just to be clear, take a bulb (dome light will do?) and run 2 wires off of it and start touching it to the sides (clamps? holders?) of each fuse station and see if there is power going across where there shouldn't be.
If my "test bulb" lights up, say, on the cigar lighter (e.g.) fuse station, then that indicates there is a "draw" on that circuit. Wouldn't that fuse be blown as well?
What if I put a 25 or 30 amp fuse in and it doesn't blow? Would that, in any way, indicate, or at least narrow the possible problem areas?
Auto repair was my son's talent, he used to do ALL the fixing/repairing and installing etc. He is no longer with us so I am doing the best I can. Never know what to say about that, except that I sincerely appreciate any and all help offered. Thanks.

 

What Macquyver is telling you to do is to take a bulb with two wires attached to it and place the two wires across the fuse that is blown. The light will be lit since you have a short. When you find the short and correct the problem the light will go out. By doing it this way you will keep from blowing fuses while searching for the problem. What I usually do is to place a ohmmeter on the load side of the fuse to ground. When the ohmmeter reads good I know I have found the short. This is just two ways of doing the same thing.

 

You can use just about any 12 volt bulb for a test light. A dome light bulb will work fine. just be careful if you leave it on for a while. It'll get hot.
The test light provides an alternate path for current, so...
With the test light connected across any two points, if there's a better way for current to travel, it will... the path of least resistance. If a fuse is good, a test light connected across that fuse will not light. If a fuse is bad (or missing), the test light completes the circuit and will light up if there is something else in the circuit to complete it. Either something has to be turned on or there is a short circuit to ground. It the test light doesn't light (across the fuse) either there is no path for the current or there isn't any current available.
With one side of the test light connected to ground, use the other end to check for power at different points.
For example;
on the hot side of the fuse, light on = good fusible link (and power to that point.
on the "cold" side of the fuse, light on = fuse good. etc.
Keep working down the line.
Putting in an oversize fuse will narrow the problem down to all the wire going to the short. It will get melted so it will be easy to trace but then you'll have to replace it.
Don't do it.
Think of electrical circuits like plumbing water circuits. Small pipes/wires for small current flow. Larger pipes/wires for more flow. Trying to get too much water through a small pipe will restrict the flow (too much resistance). Forcing it will burst the pipe. Drawing too much current through a small wire will create too much resistance in the wire, overheating it. Forcing it through (with a larger fuse) will burn it up.
If you use the dome light test light across the fuse the bulb should supply enough power to the circuit to find what's drawing the current that blows the fuse. Try starting out with the brake light switch and the turn signal switch disconnected. Eliminate any possible draw that turns on the bulb across the fuse. With the bulb off, start re-connecting things, one at a time. The circuit (or item) that turns the bulb back on is where to look.
Sorry for the long post. Hope it helps.
Greg

 

Just had a thought... Disconnect the wire to the cigarette lighter. Should be on the same circuit as the brakes and 4-ways.
(I know I could have edited, I wanted to keep this separate)

 

I knew you guys would get me going in the right direction. Got some sleep (finally). Read your replies and now it looks like a manageable situation. Just a matter of crawling back down there and eliminating one thing at a time. Hell of an idea with the bulb and wire thing. Buddy of mine has just such an apparatus he's bringing over this evening. He's never been on the internet before and wants to see what "FTE Forum" is. I'll be very proud to show him. Much appreciation.