Turn signal fuse STILL blowing (1 Viewer)

[Jonathan Hanson]

Some time ago I posted about the turn signal/voltage regulator fuse in my 73 FJ40 blowing and my turn signals/flashers going out. Then the fuse stopped blowing but the signals still didn't work. I finally traced the issue—I thought—to a burned connection to the hazard switch, in this thread. I repaired the connection and overhauled the hazard switch.

However, the fuse is still blowing; I'm virtually certain while I have a turn signal engaged. I noticed that the ammeter, which has always just ticked a bit in time with the signal, now swings wildly with it, as though a lot of excess power is being drawn. It does this when either signal is on.

It could be something as simple as a short in the factory harness, but finding that would seem to require stripping back the entire run between the switches and the tail lamps. I can't guess if it could still be a faulty hazard switch, which seemed fine when I took it apart except for the single burned connection in the wire that goes through the hazard switch to the turn signal switch. It seems obvious that the burned connection was the result of the issue, not the cause.

Any ideas about how to track down the exact location of the issue without just throwing parts at it?

Oh . . . I'm pretty certain it's not a ground issue because I ran a dedicated ground wire between the tail lamps and all the way back to the battery.

 

[rkymtnflyfisher]

Grab a multi meter and start checking resistance to ground, isolate small sections wherever you can until you figure out what section is different.

Pay attention to the small wiring section from the harness to the lamps.

 

[bikersmurf]

It is most likely unrelated, but I kept blowing fuses when the connector for the reverse light switch was bouncing into the spinning e-brake drum on the transfer case. In my case I had wired it to the headlight circuit, but I don’t know what the stock configuration would be for your year.

 

[Jonathan Hanson]

Grab a multi meter and start checking resistance to ground, isolate small sections wherever you can until you figure out what section is different.

Pay attention to the small wiring section from the harness to the lamps.

I'm a complete, utter moron on the use of an ohm meter. Can you give me more details? Test with the turn signal on? My meter has multiple ohm settings; which do I use?

 

[rkymtnflyfisher]

I'm a complete, utter moron on the use of an ohm meter. Can you give me more details? Test with the turn signal on? My meter has multiple ohm settings; which do I use?

I'm just pulling out to go somewhere, I'll try to follow up when I get back, or at least swap drivers, unless someone else chimes in.

Probably the standard 0-100 ohm settings, clamp one lead to metal, and use the other lead to check the wires that should be positive 12v power to each circuit.

Pull the connectors apart everywhere and check small sections.

You'll be hoping for a higher resistance on the wiring harness sections, and a lower number across lamps.


Gotta go now.

 

[B y r o n]

Have you changed the bulbs to higher wattage? To many watts will cause the fuse to blow.

 

[Jonathan Hanson]

Have you changed the bulbs to higher wattage? To many watts will cause the fuse to blow.

No, as a matter of fact I have LED tail lamps . . . lower draw. And a solid state flasher unit.

 

[Jonathan Hanson]

Part of the problem with diagnosing the issue is that it's not instantaneous. Sometimes I can drive for a few miles, and use the signals, with no problems except the fluctuating ammeter. Then suddenly the fuse will go. When I check for a short at the hot end of the fuse I get nothing.

 

[45Dougal]

Firstly check all your turn signals work and are the right wattage, including those on the instrument panel, and the side repeaters in the front turn signals. The front ones pass through the steel panel, so check for grommets /insulation damage - common place for an intermittent short.

How many Amps is the fuse?

What happens if you leave the hazard lights on, and what amperage is the hazard fuse?

Also worth checking the feed to the regulator on the firewall - this also passes through the bulkhead and is another good place for a short - check the grommet is intact.

A photo of your solid state arrangement might help

 

[bikersmurf]

Intermittent problems are the most difficult to diagnose.

How many amps is your multimeter rated for? If feasible I’d want to monitor how many amps are going through the fuse. Many multimeters are only rated for 10 amps which is probably less than the fuse rating. If that’s the case then we’ll have to find a different way. I’ve found auto resetting breaker (fuse) to be helpful while sorting through this sort of issue. They help avoid going through a dozen fuses while troubleshooting.

If I had to guess I’d look for points where the wiring harness could rub on the body/frame near the four turn signals. Where the wires go through at the rear of the truck and into the housings would be my first thought. Also grommets as just mentioned. It’ll likely take some careful searching.

Since it’s intermittent, I suspect the bouncing/movement of the truck is playing into it. This increases the likelihood that it’s not somewhere random within the harness, but instead at a grommet or somewhere else the hot wires are passing through metal. You may need to crawl around (while the flashers are going) and wiggle the wires to see if you can trigger the fuse to blow.

 

[Jonathan Hanson]

The turn signal/voltage regulator fuse is 15 amps; the horn/stop/hazard flasher fuse is 20 amps. All the signals work until the fuse blows. As an experiment I disconnected the solid-state flasher unit and re-connected the factory unit. The hazard flashers still work, but when I engage a turn signal either direction the dash indicator light and the bulbs light up but don't cycle.

 

[45Dougal]

The turn signal/voltage regulator fuse is 15 amps; the horn/stop/hazard flasher fuse is 20 amps. All the signals work until the fuse blows. As an experiment I disconnected the solid-state flasher unit and re-connected the factory unit. The hazard flashers still work, but when I engage a turn signal either direction the dash indicator light and the bulbs light up but don't cycle.

That's because of your led back lights - not enough Current to switch the original flasher.

Leave your hazards running for a while and wiggle things around, it would be great to blow the hazard fuse - you definitely isolate it to the turn circuit in that case rather than the regulator.

Or drive without using your turn signal and see if you can still get it to pop.