How do you test turn signal switch?

[rgunlock]

This is in a 78 GMC K15 with new AAW wiring harness and new turn signal switch (from Rockauto.com I believe). Right turn signal works fine. If I hit the lever for the left turn signal, I hear the flasher relay click about 3 times then the 10A fuse for the turn signals blows.

I've tried replacing the flasher relay module in the fuse panel but made no difference. I've removed all the bulbs from left front, side and rear and the fuse still blows after a second or so after pushing the turn signal lever to left turn.

Both turn signals have been working for the couple months that I've been driving the truck until one drive I noticed I have no turn signals - fuse is blown. Trying to narrow the problem down, the fuse blows every time after a couple seconds with the lever down for left turn signal.

So, all the wiring in the column is new, but I suppose I could have routed the wiring wrong within the column. Might be something besides the column entirely, but I've traced the wiring front and back and its all sitting snug in its conduit without any sign of wear or burns.

What else would you test? I've got a multimeter and amateur skills with it. Looking for anything to tell me whether the problem is likely in the column before I tear it apart.

Thanks --Rick

Edit: after starting this thread, I searched "test turn signal switch" and found this thread where ray_mcavoy describes testing the turn signal switch http://67-72chevytrucks.com/vboard/s...d.php?t=629205. This search worked much better than "left turn signal blows fuse". I'll be trying the tests he described.

[rgunlock]

The tests show that the turn signal switch is probably ok. I had continuity from purple to light blue and yellow with the lever in left turn position but not otherwise. Same for right turn with continuity between purple and dark blue and dark green. I jumpered between purple, yellow and light blue with key in ACC and blew the fuse. So not the turn signal switch.

To get at these connectors, I removed the lower column cover and the panel from the dash under the column. This exposed what I'll call a "harness retainer" bolted to the column at say 4 and 8 o'clock positions. Is there supposed to be any sort of insulator between the bar on this retainer heading forward and the wires into the connector? I can see a pretty good indention in all the wires insulation about an inch up from the connector where this retainer bar presses against them, but I don't think any real damage yet.

[ray_mcavoy]

Hi Rick,

Those tests I posted in that other thread were aimed primarily at finding an open circuit that was preventing the turn signal from operating. You could do a similar continuity check between the light blue "front left turn" & yellow "rear left turn/brake" wires on the switch and the steering column jacket (ground) to check for a pinched / chafed wire that is shorting to ground. But since it's still blowing the fuse when using the jumper wires (which takes the turn signal switch & column wiring out of the circuit), I think you're correct in figuring that the problem is outside of the switch.

It's been a while since I've had one apart, but I do seem to recall there being a plastic sleeve around the turn signal wires where they pass under that retainer piece on the column. It doesn't sound like you currently have a problem at that location but it might be something to consider for future protection ... especially if it looks like that retainer is leaving indentations in the wires.

I assume you're not having any problems with the brake lights blowing the fuse, correct? That would rule out a problem with the yellow wire that runs to the left rear turn signal (and is shared with the brake light). So you can concentrate on searching for the problem in the left front turn signal circuit.

The light blue wire for the left front turn signal usually has 2 branches. One that runs out to the front of the truck and another that goes to the indicator on the dash. So if you haven't done so already, you might want to try temporarily unplugging the instrument cluster connector to see if the short is possibly in the cluster indicator portion of the circuit.

[rgunlock]

So I reconnected the column harness. Next step was to to isolate the turn signal indicator bulbs in the cluster. So I removed the cluster, put in a new fuse and voila, both turn signals work and no fuse "pfftt".

Flipped over the cluster and I'm thinking that printed circuit section going to the left turn indicator bulb looks a bit shady. I'd noticed before that it was kind of kinked up but it was working so... I'm debating whether it is time to order a new circuit sheet. I've already had to glue all the copper fingers for the harness connector back down. But, while I'm no whiz at soldering I may first try cutting that bad section out and soldering little jumper wires across to the bulb base.

Guess I could cut that section out first and reconnect the cluster to make sure that eliminates the blown fuse problem.

[rgunlock]

Originally Posted by ray_mcavoy

Hi Rick,

Those tests I posted in that other thread were aimed primarily at finding an open circuit that was preventing the turn signal from operating. You could do a similar continuity check between the light blue "front left turn" & yellow "rear left turn/brake" wires on the switch and the steering column jacket (ground) to check for a pinched / chafed wire that is shorting to ground. But since it's still blowing the fuse when using the jumper wires (which takes the turn signal switch & column wiring out of the circuit), I think you're correct in figuring that the problem is outside of the switch.

It's been a while since I've had one apart, but I do seem to recall there being a plastic sleeve around the turn signal wires where they pass under that retainer piece on the column. It doesn't sound like you currently have a problem at that location but it might be something to consider for future protection ... especially if it looks like that retainer is leaving indentations in the wires.

I assume you're not having any problems with the brake lights blowing the fuse, correct? That would rule out a problem with the yellow wire that runs to the left rear turn signal (and is shared with the brake light). So you can concentrate on searching for the problem in the left front turn signal circuit.

The light blue wire for the left front turn signal usually has 2 branches. One that runs out to the front of the truck and another that goes to the indicator on the dash. So if you haven't done so already, you might want to try temporarily unplugging the instrument cluster connector to see if the short is possibly in the cluster indicator portion of the circuit.

Thanks Ray! I think our posts crossed on the internet wire I found a roll of adhesive foam left over from mounting my toolbox on my bed and lined the inside of the retainer piece with some of that. I think that should protect the wires. And the guage cluster was my next step which I described in the previous post. Now I just need to determine whether that squirrely section of printed circuit going to the left turn indicator is the actual problem. Sure looks like it could be.

[ray_mcavoy]

Hi Rick,

Yeah, looks like you were already on the right track with checking the instrument cluster. And you're right, those damaged traces leading to the indicator light sure do look like they could be the source of your short circuit.

A new replacement printed circuit might not be a bad idea (especially since they are available for most of these trucks). But in cases where replacements weren't readily available (or the damage was minimal), I have repaired some by soldering in sections of wire to bridge across damaged areas. You have to get the wire soldered into place fairly quickly and not keep the soldering iron on the trace for too long, otherwise it has a tendency to melt the plastic backing and make a mess. On yours, it looks like the traces are still intact (just pulled away from the backing & likely touching / shorting together). So you might be able to separate them and glue them back down without having to do any soldering.

[franken]

I've seen junk Asian turn/park sockets for 1157 bulbs that caused shorts.Maybe take a bulb out and see what it does when the signal is on.

[rgunlock]

Originally Posted by ray_mcavoy

Hi Rick,

On yours, it looks like the traces are still intact (just pulled away from the backing & likely touching / shorting together). So you might be able to separate them and glue them back down without having to do any soldering.

By the time I read this, I'd already cut out that section. Good news is that seems to be the problem because I was able to plug the cluster back in and the left turn signal works (externally) without blowing the fuse.

Originally Posted by franken

I've seen junk Asian turn/park sockets for 1157 bulbs that caused shorts.Maybe take a bulb out and see what it does when the signal is on.

Thanks franken, but I've already tried pulling the bulbs and I'm pretty sure I've narrowed this down to the guage cluster.

I did mention I'm no whiz at soldering and my equipment basically sucks but I gave it a shot. As Ray predicted I made a mess of it so gave that up. For now, I'll put the cluster back in and drive the truck without a left turn indicator light in the dash.

I'll be shopping for a new cluster circuit sheet to hopefully get everything right again - this isn't the first electrical gremlin I've had to chase with this truck build, and I think this is the 20th time I've had to pull the cluster - dang tired of doing that!

Thanks for your suggestions. Between thinking about what to write in these posts causing me to "think" and the suggestions, it really helps me out.

[TKCR]

Originally Posted by rgunlock

I'll be shopping for a new cluster circuit sheet to hopefully get everything right again - this isn't the first electrical gremlin I've had to chase with this truck build, and I think this is the 20th time I've had to pull the cluster - dang tired of doing that!

I bet your getting really good at it then, lol. I hate chasing down electrical issues. I did this where I work for many years, but I was getting paid, big difference!! Hopefully the new sheet will work!!