wires are metal ...

couldn't be bothered to fix . One thing is the radio power supply . He did tell me that the radio had "died" , turns out the fuse (in the fuse
block) keeps blowing . I've got the dashboard apart enough to check the wiring harness and supply wires , can't find any cuts or anything that looks like damaged insulation ... it works just fine sittin' in the driveway , but within a few miles driving it blows the fuse . I figured it was the radio/CD player unit so I got a new one , does the same thing . I'm really puzzled by this , from the way the fuse was spattered it's got to be a dead short to ground . I think it very unlikely that the new radio/CD unit is bad - the old one did work when I replaced the fuse , for a few miles same as the new unit . This is an '86 GMC pickup , I'm hoping someone here might be aware of a known problem area that I might check ... I gotta have tunes !
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On Sep 24, 2019, Terry Coombs wrote

over time the wire insulation was worn through, allowing contact between copper wire and some part of the steel body.When you find the spot, it will be pretty obvious visually.
Solution is to find out where this is happening, and mechanically prevent further contact.
Joe Gwinn
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On 9/24/2019 9:03 AM, Joseph Gwinn wrote:


The problem is finding that spot ... if it was obvious I'd have found it by now . I've looked and felt as much of that harness as is available to check , nothing so far . I'm starting to wonder if it's in/near the fuse block , maybe where the under-dash wiring comes from behind the block . But it's raining today , and I'll be too busy to look into it further until Friday or Saturday .
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Taping possible contact areas may help.
This has been useful when there are no voltage-sensitive components at risk, like older appliances: (Amazon.com product link shortened)
Battery-powered ones are more convenient, but don't stop generating if you get shocked.
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On 9/24/2019 10:07 AM, Jim Wilkins wrote:


to wiring diagrams , which led my eventually to a forum post that indicates that power lead goes straight and only to the radio . It comes out of the harness with the correct other wires . I have traced that harness from the fuse block to the radio and find no damage or rubs or torn wrap . My next step will be to pull the fuse block from the firewall and check for problems on the back side . Gotta pull the plug off from the rngine side first , and that ain't happenin' in the rain .
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My truck sat idle for 3 years because I couldn't locate an intermittent electrical fault, despite disassembling and cleaning all the engine connectors and replacing most of the components. I finally bought the factory engine and emission manual from Ebay and used it to find the problem with an oscilloscope.
I hadn't replaced the ignition module because its mounting screws were corroded in place. When it tested questionable and I did remove it one broke and I had to make a drill jig to bore out the steel screw without ruining the aluminum intake manifold's threads.
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On Tue, 24 Sep 2019 13:03:21 -0400, "Jim Wilkins"
--snip--

Wild one, Jim.
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are a people, and not a polyglot boarding house.
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On 9/24/2019 9:50 AM, Terry Coombs wrote:



If you know where it comes out of the fuse block. cut it at about 8", connect a new wire, run that up to the radio and do the same at the other end. Give yourself 8" out of the radio connector and connect your new wire. Also, I would have taken the connector loose from the radio and drove it before I got a new radio, just to verify, harness or radio. Mikek
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On 9/24/2019 4:45 PM, amdx wrote:






back-light on the faceplate died some time ago and it has no aux inputs . As I mentioned here somewhere , I'll be looking into doing what you suggest on Friday . Tied up until then .
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On Tuesday, September 24, 2019 at 5:45:32 PM UTC-4, amdx wrote:

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Good plan, but... After cutting the wire a few inches out of the fuse block , I'd drive a few miles to make sure it doesn't blow the fuse. There's got to be some version of Murphy's Law that says the short will be in the wire you didn't check separately.
Also, a multimeter with a continuity beeper could be a friend here. Hook it up between the supply wire and ground (fuse pulled first) and then wiggle all the wires. When it beeps, you've found your short.
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On 9/28/2019 9:15 AM, rangerssuck wrote:

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lock, I'd drive a few miles to make sure it doesn't blow the fuse. There' s got to be some version of Murphy's Law that says the short will be in t he wire you didn't check separately.

k it up between the supply wire and ground (fuse pulled first) and then w iggle all the wires. When it beeps, you've found your short.

Is the radio the only thing that's on that fuse? I'd run a new wire with an inline fuse from the radio to the battery and see what happens. Are you s ure the problem isn't in the radio?
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wrote:



As noted on another group the trasnmission torqueconverter lockup runs off that fuse too. Since the transmission swap was a "shade tree job" the chances of it being related to the transmission replacement are roughly 1000% - - - - - - - When the controls call for TC lockup the fuse blows.
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On my Honda the TC lockup occurs only in the highest gears, at constant speed on a level road, an easy condition to test with the radio unplugged. I can tell when it's locked because the speedo and tach needles move together.
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On 9/28/2019 3:34 PM, Clare Snyder wrote:



is (with 99.99% assurance) the problem . I'll get under there tomorrow and find where it's grounding , but I did a road test with speeds high enough to call for lockup with that wire unplugged and the fuse is still intact . The internet truly is an information highway . I would never have known that device was powered by the same fuse as the radio .
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On 9/28/2019 4:27 PM, Terry Coombs wrote:

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There are times when having a complete wiring diagram can be a big help. :-) What's on the load side of the TC lockup output A solenoid or some such? shorted?
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On 9/28/2019 6:39 PM, gray_wolf wrote:









column to where it plugs in to a device - probably a relay of some kind - mounted on the steering column . It comes out on a blue which goes thru the firewall alone then to a small bundle that heads towards the tranny . My guess is that the blue wire plugs (or is supposed to) into the lockup solenoid , and is either unhooked or damaged and grounded . I'll find out in the morning . My wife has resigned herself to me keeping this truck , but that don't mean she's happy about it . I've also got a set of 3.42:1 gears for the rear axle , the 2.73's just don't get it up here in the "mountains" - I grew up in the "real" mountains , northern Utahaha at the foot of the Wasatch Front .
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On Sat, 28 Sep 2019 19:07:56 -0500
<snip>

Mines an 1982 K10 4x4 with same tranny...
The wire goes to a switch on the brake pedal, out to a switch on the throttle and then to the tranny. Stepping on the brake or not enough throttle unlocks the torque converter clutch.
On my truck the torque can lock in second gear if all the above conditions are met. i.e. enough throttle, no brake and going fast enough. However if you are in 4x4 it will only lock in overdrive/4th gear. I added a switch early on to make it think it was in 4x4 so it will only lockup in overdrive while in 2 wheel drive.
This was in 1982, maybe they wised up and did my hack to all later on. That 700R4 is not a real solid, heavy duty tranny. Never should have been used in trucks...
--
Leon Fisk
Grand Rapids MI
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On 9/29/2019 7:30 AM, Leon Fisk wrote:

determine the exact path that blue wire takes . That switch on the column may very well be a switch associated with the brake . One test I thought of last night while trying to get to sleep is to disconnect the plug on the column and see if the blue wire is grounded . I've never had to deal with wiring faults that much , this has been a really frustrating experience .
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On Sun, 29 Sep 2019 08:27:46 -0500

A word of caution, pretty sure the control for the torque converter lockup goes to a solenoid in the transmission. So it will show a very low ohm value that looks like a short circuit to a meter. It should draw about 0.5 amps when working.
If I recall correctly the wire harness plugs in from the top on the drivers side of the transmission. Maybe 6-8 inches farther to the rear from the shifter linkage. Check that it was plugged in correctly and that cable isn't pinched somewhere going towards the engine...
Big ass picture here showing the cable & connector in white:
http://www.rowand.net/Shop/Tech/images/TH700R4Pictures12.jpg
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wrote:

That would be around 24 Ohms, which should show clearly on a decent digital meter. Subtract out the reading with the probes shorted
Schematic "Power Side Control #3" indicates that pin D will short to ground when the TCC Signal Switch operates. If the plug can be rotated, could pin D have been misconnected to pin B that brings power for the solenoid? The solenoid pin should show up as a low but not zero resistance to the case.
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