1970 Indicator Fuse keep blowing

[Matt G]

Looking for a quick shortcut - if anyone can help.
My 25A Indicator fuse keeps blowing.  I can't find a common scenario when it blows.  I.e., left turn or right turn, or Indicator and Brake together, etc.  generally lasts about 5mins before she pops.
Has anyone had the same problem and can point to the most likely suspect, (and where I might find it in my electrical system)?
Appreciate any shared shortcuts.

[RHD.68.l89]

LH or RH drive? It makes a difference, wiring has to be messed with for RHD. All red taillights or amber indicators?

[Matt G]

LH drive 😁

[Matt G]

Sorry, forgot to mention... tail lights are original red lenses

[RHD.68.l89]

Pink wire to the flasher can from the fuse box. Purple to the harmonica connector on the column.
The turn signal flasher is under the pass dash on a 68, should be the same on a 70. the flasher on the fuse box is hazards only.
If it working for 5 mins then blowing, is it getting hot immediately you replace it or does the car need to be moving?
if the car needs to be moving it sounds like an intermittent short which is the hardest to find.
Pull the flasher first and see if the fuse blows. put it back if all OK and disconnect the column connector. tilt column? wires might be pinched inside.
Let us know how it goes.

[sabre]

Sounds like an intermittent short. Do yourself a favour and make a diagnostic tool. Get a high wattage light (headlight or brake light) and solder 2 leads with aligator clips. Substitute the fuse with the light and start wiggling and switching. Should light dimly when indicators are on and bright when there is a short.

[Matt G]

Thanks guys.  Loads of wisdom in there!  Flasher should be under the passenger dash according to my assembly manual.  I don't know if it's a moving issue (intermittent short), but that should be pretty easy to test.  Pulling the flasher is another pretty easy check.  No tilt steering, so there shouldn't be a pinch.  I love the idea of the light soldered in to the fuse panel to high"light" (heehee ) the problem area.  Extremely logical and simple, yet still such a brilliant tool to help.
Thanks a bunch guys!

[Matt G]

Hi guys, short update.
Flasher unit was buried up behind my passenger side cool air duct.  Pulled out and all okay, nothing popped.  I repositioned it to the top of my heater box so that it was a little more accessible.  I ran my indicators (with the motor off) for a while and started jiggling wires, turning steering, etc, etc and they were all good.  No issues found.  I thought that maybe my flasher may have been shorting on something in its old position, so I went for a drive again, and after the first use it was gone.
It doesn't seem to pop when I'm using it.  It cancels normally, etc, however the next time that I need to use it, there's nothing.  Hazards appear to be completely independent (but only tested while static).  It doesn't appear to be left or right hand turn dependent.
Next steps were going to be:
- turn on my left and leave it for a couple of hours to see  if it pops without any movement, engine heat, etc.
- repeat for the right
- Repeat with my hazards
If any of the above sets it off, then I'll replace the flasher units (I can't think of anything else that could cause it in this situation....)
- drop my steering, pull my instrument cluster and visually inspect all wires while using my indicators.
I thought more on the headlight scenario, and scared myself with some logic...  That being: If I'm popping fuses (pretty violent fuse wire burn on inspection of spent fuses), then if I allow that current to flow (through a headlight), I'd essentially be passing bucket loads of current through wires that my fuse is trying to protect.  I'm just a wee bit scared that dust, old wires, fibreglass and Murphy' law means that I stand a good chance of melting a wire in the wrong spot potentially giving my wife her corvette insurance money dream...
Feedback and ideas (as always) are really appreciated.

[Vettech]

Just about to go for a late xmas lunch/tea, and have my internet back on line.

Questionsss.
1. Do you have cct diagram.
2. The fuse "NEVER" blows if using emergency flashers.
3. So car not butchered with LH/RH conversion.
4. You have not changed the flasher can.

I cant remember if this applies to 70 GM stuff, but the flasher may be the type that needs a level of load (current) flowing thru it to govern speed of flash etc.
Is the speed of indicator flash normal, does it speed up or down.
Since the E'flashers work fine, and in this mode all blinker lamps are flashed in unison, this mode represents max load thru the f/can.

If fuse ok in extented E'flasher mode then I would assess nil wrong with any indicator lamp wiring.

I would concentrate on cct in the dash and steer collumn.
Sorry have been told to get in car, by for now ......... cans are cheap!

[Matt G]

Thanks Vettech, I appreciate the reply.
Answers:
1. Yes, but I appear to be lacking in skill. I'll try to read again tonight to see if I can figure it out.
2. Correct. Note that my e/flashers are on a different fuse AND on a different flasher (plugged above the fuse panel).
3. Correct. It's still left hand drive, however the wiring is messy, so I would think that some parts are clean and original, but I've worked through loads of really messy, non-original wiring, so I can't claim original wiring harnesses. I would think about 60% under the dash is original, now 85% under the hood, 95% at the rear and front.
4. No, I have not changed the flasher can for either the e/flashers, or indicators.

Indicator flasher does have a parallel resistor (or similar) on the mount for the flasher can.
Eflasher fuse is fine, however I have not taken a drive with the flashers on. I will try this to see if I blow the eflasher fuse.
Thanks again for the help.

[sabre]

I thought more on the headlight scenario, and scared myself with some logic...  That being: If I'm popping fuses (pretty violent fuse wire burn on inspection of spent fuses), then if I allow that current to flow (through a headlight), I'd essentially be passing bucket loads of current through wires that my fuse is trying to protect.  I'm just a wee bit scared that dust, old wires, fibreglass and Murphy' law means that I stand a good chance of melting a wire in the wrong spot potentially giving my wife her corvette insurance money dream...
Feedback and ideas (as always) are really appreciated.

Hi Matt
The idea of the headlight is to both give an indication of the current flowing (full on - there's a short, dim - normal load) and to limit the current flowing. A normal 60W headlight will limit current to 5A even if there is a dead short. Since a headlight circuit is usually designed to handle 15 to 25 A, the headlight will protect the wiring. It's an old trick. The only thing you should be aware of is that the flashers will run slow because of the reduced voltage dropping across the light.
I'd be looking closely around the tail light wiring too. The original flashers used the brake lights. Normally a new wire is added for the brakes and original wires kept for the flashers. I've seen some pretty dodgy splices doing this.

[Matt G]

Thanks a bunch Sabre. The headlight logic makes sense. I'll check the rear wiring, but I think it's more likely to be in my steering column/dash. I had some repairs done a few months ago, and I know that he had to drop the steering and pull the driver's dash cluster.  I'm leaning towards him pinching the series of wires that run bottom side of my steering column. I'll definitely hook up a light.

[Vettech]

Yes Sabre I forgot about that, the extra wire to the rear to divide the brake and flashers.

Worth a look, esp if you can put a test lamp or buzzer and get under the rear and wiggle.

However, I used to work Maint along side of construction (NDC) staff, and 89% of faults were caused by their work.
Now you have mentioned some one else working on it, as a suspicious mongrel I would immediately suspect him/her.

[Matt G]

Got it. Thanks guys. I'll check the rear (pretty easy with a good light and some persistence...).  I got my wiring diagram stitched together. Might be a few drinks before I manage to join the dots, and then a few more before I figure it all out...

[Matt G]

Hey guys. Massive, massive thanks to Garry/Sabre. After almost a couple of hours of jiggling wires, looms and connections while watching the test bulb, and with Garry's fantastic experience (and work pit), we found the short via my back-up switch wires that had burnt through on my exhaust and randomly grounded on the flange of my headers.  A huge help. Thanks again Garry. I hope to be able to return the favour one day, or similarly help another member.  For me, this type of help and experience is what it's all about...
cheers to all who volunteered experience and help!!🍺

[sabre]

No worries Matt.
And yes, absolutely right. Helping each other out is what a club should be all about.

[Vettech]

Well done guys, and the most important part of this exercise, was the feedback once the fault was found.

So often things come up on the forum, they either, are fixed or just die away, with no resolution or feedback.

Regards.