Turned hazard lights and all work , so dont know what it is.
I checked grounds, they are good and tight, but I was curious how many grounds there should be. I have one on each side of radiator bolted to rad core support. Is there a separate ground wire for turn signals?
I did do a lot of work to truck since I have had it, but cant honestly say if this problem was there when I got truck.
I will keep searching...........
Check the grounding for the rear lighting. GM wiring diagrams always show a well designed ground circuit. Typically it is shown as a single common frame ground (bolted to the middle of the rear crossmember) which then splits into two independent branches. They then branch off and lead to the lighting assembly on either side. It looks real professional - on paper. In real life however, I've never seen it done that way.
What you actually get for the rear lighting ground circuit goes basically like this:
All the ground leads from one side are spliced together (which side varies with model year and body style). That spliced connection is then lead over to the other side where it ties into another splice - which consists of all the ground legs from lamps on that side. But there is an extra lead twisted into that bowl of spaghetti. That lead is meant to provide the ground path for the entire combined LH/RH lighting group. In my limited experience it is always just a 6-8 inch piece of wire with a flimsy ring terminal on the end. That ring terminal is secured to the back of the "destination" assembly with a sheet metal screw. Below are some photos of a rear lighting harness I surgically removed from a 1987 K10 Sierra Classic a couple of years ago. It was OEM and in great condition - way better than mine - so I grabbed it.
Notice that there is no local grounding point provided for one of the sides (I forget which side) and also that the only ground for those six lamps is via the short lead/ring terminal on the opposite side -
there is no common ground to the frame.
First is how GM typically represents the circuit - in it's wiring diagrams and service manuals (blue tracer is for clarity):
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But in reality, this is what it actually consists of:
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There is a reason I bring this up. Thermal relays are cycled on/off by current flowing through a bimetallic strip. How they work isn't within the scope of this discussion. But suffice it to say that; the greater the degree of current flow through the flasher, the faster it will cycle on/off.
Your e-flashers will cycle the LH lamps on/off, but the turn signal flasher will not cycle that side - even though it is supplying current to the same filaments (and through the same leads) as the hazard flasher. This is a stretch, but the key difference between the two flashers is that when the hazard flasher is operating, it is supplying power to the lamps on both sides of truck. On the other hand, when the you activate the directionals, power flows to only the one side you selected. So, it follows that the hazard flasher is always supplying power to twice as many lamps as the T/S flasher.
My point is that if there is an insufficient grounding condition anywhere in the LH hazard/directional circuit, it may be reducing the current flow through the bimetallic strip - to the point where the strip doesn't get hot enough to open/close. The lights come on, but won't cycle off. The same reduced current flow on the LH side will of course affect the hazard flasher. But since it is also supplying the lamps on the RH side - there may still be sufficient flow to allow it to cycle.
You seem to have done a thorough job checking the grounding for the front part of the lighting circuit. And, because the rear grounding setup is so fragile in comparison, I thought I should suggest you check it. That is the reason for tonight's long, boring post. Also my wife and daughter are on vacation in Spain and I have nothing to do.
Good luck. This is a real head scratcher.
