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74 620 Speedo cable and starter issues


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my Speedo was acting funny on my last trip over the grapevine, started bouncing around up and down 20-40 mph, until it finally just stopped giving any kind of an accurate reading past 30 or 40 mph. so now if I'm doing 60 or 70 my Speedo is buried all the way back around to under 0.


is this just a cable swap solution or is something else going on? what causes this to happen?


also, I'm guessing my starter went out the other day, idk parked it for 30 minutes came back out and the sucker wouldn't even turn over or crank once. I'm getting power to the starter wire, so I just pulled it and am on my way to get the new one. - i guess my question is, is it common for Datsun starters to just quit without any signs of hard starting or struggling?


thanks for the input.

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Sometimes things on these old trucks will come loose. 


The speedo cable could be loose at the transmission and or at the cluster. this will cause jumping and erratic movement of the needle. 


Have them test the starter. Was it clicking or making any noises when you tried to start it? 

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The starter have absolutely no indication of going out. no clicks, no hard starts, nothing. I spoke with 3 different mechanics and they all concluded starters can go out without warning. this is the first me or my dad have experienced a starter just die without warning. still waiting on the starter to come in, I forgot to ask them to check it when I dropped off the core. 30 bucks and 20 minutes I'll just replace it. :)


the Speedo cable is solid to the transmission, I can't even losen it with my fingers. however there are two wires that attach to the trans ahead of the Speedo cable, what are those?


also thanks for the suggestion about checking the back of the gauge cluster, since it seems right at the trans, I hope the issue is back there.

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although I've only had the truck since Feb and maybe it's been hard starti g the whole time lol


I also checked and saw that the starter was getting power which is why I went ahead and pulled it and am going to replace.


I'm also getting power at the back of the ignition switch.

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If the speedo needle is pegged it's usually not the cable.  Something internal in the speedometer itself likely broke or came loose and is causing the magnet pickup to drag.  I've had one break, only recourse is to replace it.  Fortunately all 620 speedos are internally identical (78-79 ones have KpH markings in addition to the MPH ones) and there are switches depending on year/transmission but those can be swapped/removed as necessary.


The wires on the transmission are for reverse lights and possibly top gear switch for an emissions component.



Yeah, always test the starters first.  7/10 the problem is corrosion or a broken cable.  It'll show voltage under no load but under load, too much resistance.  BUT- if the solenoid was sticking it may have come loose just by removing it and it could fail again. 

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Erratic running is the inner cable rubbing against the inside of the outer sheath. The inner cable is just a vary long flexible coiled spring. It catches in the inner sheath but the transmission keeps turning it. Energy is stored and when it comes loose it makes the needle jump. You can replace it OR. Use pliers to looks the transmission end and carefully pull it out and lubricate it. It's very slippery an floppy so gave something clean for it to fall out on. 

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I took the truck to the mechanic I bought it from since he wired in the alarm, he's not sure what's up either, I may take it back to him later today...

the truck has a pull chain that kills the power, I was told primarily for the radio. I think this is causing problems somewhere as prior to the other day I could toggle the pull chain off and on with the truck running and it would make no difference; where as currently if I toggle the pull chain it will kill the engine. perhaps something got crossed? or shorted somewhere, also the alarm system is unlocking the doors when I turn the ignition key to the start position where it previously would lock them.

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What TF is a pull chain? and how does that kill the power??


Someone has Mickey Moused the ignition (maybe for a kill switch) so I would get it back to stock condition first.

Maybe it's one of those pull switches like you find on a lamp.


Here's a link to the electrical schematic for your 620.



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Put a relay in the starting circuit, works 100% of the time unless the starter is dead.  Used them in VW's for 30 years.

I use the old metal bodied Ford starter relays. For massive electronics, I use the continuous duty solenoids. They're basically the same but the starter relay has 3 pins and the continuous duty has 4.

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