Clicking when lights are on?
Thread Starter
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Fleet Mechanic
Joined: Jul 2004
Posts: 1,988
Likes: 14
From: Travelers Rest SC
Clicking when lights are on?
I'm digging in to my '72 F-250, fixing all the little issues. Many of the lights don't work. When I turn on the lights, there is a clicking coming from a relay (?) next to the glove box. It clicks; the lights go dim (but not out) for a few seconds, then it clicks again and they brighten back up. My guess is a weak short overheating the relay. It happens whether the parking lights are on, or full headlights. How do I track this down? The wiring in the rear has been hacked and cobbled together by unknown hands- good chance the trouble is there somewhere.
Next up will be the turn signals- I'm not getting anything there at all!
Next up will be the turn signals- I'm not getting anything there at all!
Lead Driver
Joined: Jan 2003
Posts: 9,893
Likes: 12
From: Ohio
There is no relay on the lights on these trucks(unlike newer trucks). The headlight switch does have a built in circuit breaker. Typically they get old and weak and if you have newer halogen bulbs up front it will start to blink on/off due to excessive current draw through the headlight switch.
What sounds like you have is a short out back(cobbled up wiring) and it is back feeding into the turn signal flasher. Best guess is your rear parking lights.
Here is the lowdown. There are only FOUR wires going to the back of the truck. I would get under there and find the original four wires and disconnect them from everything. Now see if your headlights function correctly. Yes? Okay.
Those four wires are such:
LEFT TURN/BRAKE
RIGHT TURN/BRAKE
PARKING LIGHT
BACK UP LIGHTS
With a test light you can go through them one at a time and hook them up properly and have nice working tail lights.
What sounds like you have is a short out back(cobbled up wiring) and it is back feeding into the turn signal flasher. Best guess is your rear parking lights.
Here is the lowdown. There are only FOUR wires going to the back of the truck. I would get under there and find the original four wires and disconnect them from everything. Now see if your headlights function correctly. Yes? Okay.
Those four wires are such:
LEFT TURN/BRAKE
RIGHT TURN/BRAKE
PARKING LIGHT
BACK UP LIGHTS
With a test light you can go through them one at a time and hook them up properly and have nice working tail lights.
Hotshot
Joined: Mar 2013
Posts: 14,255
Likes: 199
From: Phoenix, Az.
2X Freightrain on the headlamps but i kinda remember a relay over there for the Camper wiring. I am assuming this F250 is a C/S. I'll dig in to that in a second but this will help with the tailamps.
Thread Starter
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Fleet Mechanic
Joined: Jul 2004
Posts: 1,988
Likes: 14
From: Travelers Rest SC
Yes, it's a Camper Special. There's something that looks like a relay all the way over on the right- the only reason I can see it is because the glove box liner is missing. That's what's clicking. I suspect the rear wiring, because it happens whether I put full headlights on, or just the parking lights. Normally, parking lights wouldn't be anywhere near enough to make something kick out.
I had the same thought for the tail lights- just strip away everything but the original cable, and patiently track it down and re-wire the tail lights. I can add the trailer wiring later.
I had the same thought for the tail lights- just strip away everything but the original cable, and patiently track it down and re-wire the tail lights. I can add the trailer wiring later.
Lead Driver
Joined: Jan 2003
Posts: 9,893
Likes: 12
From: Ohio
Is that relay a power source for a slide in camper? Powered when you turn on the lights? Still thinking the wiring in the back might have some affect and the source of the short.
How's the wiring under the dash? Anything cut/chopped up there that could be a problem?
How's the wiring under the dash? Anything cut/chopped up there that could be a problem?
Elder User
Joined: Jul 2012
Posts: 553
Likes: 0
From: Raleigh, NC
Might the relay(?) be a self resetting circuit breaker? If it is, I'm guessing the problem is the output wire from that circuit breaker is shorted out and the circuit breaker gets power from the light switch. Lights dim when the breaker is closed, goes back to bright when the breaker is open.
You could disconnect the output wire from that circuit breaker and test for continuity to ground or ohms close to zero. If the wire is grounded, follow it to the problem.
Turn signals might be a whole different problem, e.g. flasher or TS switch.
You could disconnect the output wire from that circuit breaker and test for continuity to ground or ohms close to zero. If the wire is grounded, follow it to the problem.
Turn signals might be a whole different problem, e.g. flasher or TS switch.
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Hotshot
Joined: May 2004
Posts: 12,170
Likes: 5
From: The hills of No. Calif.
Yes, there is a sort of relay there. It's the thermal breaker. This is a common problem, my '68 suffers from a similar (and related) problem: When I drive for any length of time with the high beams on, the relay gets hot and kills them completely, they stay of for several seconds and then come back on, only to blink off again a minute or so later. No problem on low beams though. There's a fix for it, which I haven't done yet but plan to. Here's the article about it:
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Thread Starter
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Fleet Mechanic
Joined: Jul 2004
Posts: 1,988
Likes: 14
From: Travelers Rest SC
The tail light wiring is hopelessly complicated. There are two factory harnesses, one with 7 wires and one with 10 (!). I disconnected everything back there, and the clicking continues.
The light relay or circuit breaker is hard to get at- I'll probably have to remove the A/C unit from the cab (it's probably junk anyway). I would think if it were a circuit breaker, the lights would go OUT when it cycles, not just dim.
It's looking like this truck would be a good candidate for an after-market wiring harness. Much of the original wiring is cracked in various places. I guess I won't be getting on the road any time soon. There are actually only a few electrical things that DO work.
The light relay or circuit breaker is hard to get at- I'll probably have to remove the A/C unit from the cab (it's probably junk anyway). I would think if it were a circuit breaker, the lights would go OUT when it cycles, not just dim.
It's looking like this truck would be a good candidate for an after-market wiring harness. Much of the original wiring is cracked in various places. I guess I won't be getting on the road any time soon. There are actually only a few electrical things that DO work.
Elder User
Joined: Jul 2012
Posts: 553
Likes: 0
From: Raleigh, NC
The tail light wiring is hopelessly complicated. There are two factory harnesses, one with 7 wires and one with 10 (!). I disconnected everything back there, and the clicking continues.
The light relay or circuit breaker is hard to get at- I'll probably have to remove the A/C unit from the cab (it's probably junk anyway). I would think if it were a circuit breaker, the lights would go OUT when it cycles, not just dim.
It's looking like this truck would be a good candidate for an after-market wiring harness. Much of the original wiring is cracked in various places. I guess I won't be getting on the road any time soon. There are actually only a few electrical things that DO work.
The light relay or circuit breaker is hard to get at- I'll probably have to remove the A/C unit from the cab (it's probably junk anyway). I would think if it were a circuit breaker, the lights would go OUT when it cycles, not just dim.
It's looking like this truck would be a good candidate for an after-market wiring harness. Much of the original wiring is cracked in various places. I guess I won't be getting on the road any time soon. There are actually only a few electrical things that DO work.
I'd cut the wire that's downstream from the circuit breaker and see if your lights stay bright.
BTW, I put all new wiring in my '70 F100. I hope I never have to do another one. If the only wires that are really messed up are to the rear, that part would be pretty simple, and a whole lot cheaper, to replace.
Lead Driver
Joined: Jan 2003
Posts: 9,893
Likes: 12
From: Ohio
^^^That is what is cornfusing me after rereading the situation. It trips the relay/circuit breaker and the lights go DIM. That is backwards. UNLESS it is tripping from some reason and dead shorting and killing the battery(thus making the lights go dim).
Time to put a volt meter on the battery and watch it.
Like mentioned, you need to remove power from that circuit and see what happens. Anyone has the wiring diagram for a C/S??
About 4 yrs ago I scrapped my '67 F100. I pulled the COMPLETE harness out and sold it. Everything from front to back. It was totally unmolested and perfect condition. Nothing cut, nothing added. Compared to some of the trucks you read about, it was one of a kind. Too bad the body was junk.
Time to put a volt meter on the battery and watch it.
Like mentioned, you need to remove power from that circuit and see what happens. Anyone has the wiring diagram for a C/S??
About 4 yrs ago I scrapped my '67 F100. I pulled the COMPLETE harness out and sold it. Everything from front to back. It was totally unmolested and perfect condition. Nothing cut, nothing added. Compared to some of the trucks you read about, it was one of a kind. Too bad the body was junk.
Hotshot
Joined: Mar 2013
Posts: 14,255
Likes: 199
From: Phoenix, Az.
I still say delete all the mess the PO did and the problem might go away. I bet there is a mile of wire spagetti under that dash. Po probably used the hot wire going to the headlamp switch to power the radio,amplifier, etc. Whatever curcuit that goes through that breaker is probably overloaded.
Mark and unhook all the aftermarket wiring and see if they Dim. A "pop" to me if they stay bright
.
Mark and unhook all the aftermarket wiring and see if they Dim. A "pop" to me if they stay bright
.
Elder User
Joined: Jul 2012
Posts: 553
Likes: 0
From: Raleigh, NC
Complete replacement with an OEM set of wires sounds good if the truck is original and you can find a good set. I installed an "E Z WIRING" harness/fuse block and it was a nightmare. But then, I had some add ons like later steering column, elect fan and controller, 3G alternator, trans controller, aftermarket gauges, etc. Not fun!!!
Thread Starter
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Fleet Mechanic
Joined: Jul 2004
Posts: 1,988
Likes: 14
From: Travelers Rest SC
I haven't pulled the dash yet, but I will, because none of that is working, either. The device in question is permanently wired, with a short harness that unplugs. There is one fairly thin wire in the center, and a thick wire on either side of it. I have no idea which wire goes where, but I assume the center wire is the 'signal' from the light switch, and one thick wire is power coming in, and the other is power to the lights. In that case, it is a relay of sorts.
All I've learned so far is that the rear of the truck isn't the problem. So far, the headlight and parking light wiring in the front appears to be stock and un-cut.
I still don't understand why the lights are dimming when it clicks in (or out). If it's a circuit breaker, they should go out if it disconnects. If there is a short that's sucking current, and that makes the lights dim, then where are the lights getting their power from when the breaker trips? I'll try to get a voltmeter in there and see if I can determine what the role of each wire is.
All I've learned so far is that the rear of the truck isn't the problem. So far, the headlight and parking light wiring in the front appears to be stock and un-cut.
I still don't understand why the lights are dimming when it clicks in (or out). If it's a circuit breaker, they should go out if it disconnects. If there is a short that's sucking current, and that makes the lights dim, then where are the lights getting their power from when the breaker trips? I'll try to get a voltmeter in there and see if I can determine what the role of each wire is.