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I finally got my '73 Datsun 620 running, and it runs good! Well, at least excluding the carburetor problems, but thats another post...


More to the point, there are some electrical issues to be resolved. The two that concern me most are that the Speedometer doesn't work and that the blinkers almost don't work (more on that later). All my warning lights work, but neither the temp nor gas gauge work. All my fuses are good, I checked that.


The first thing that came to my mind for the speedometer was that the cable was broken, but I pulled it out, and it was good. Where it goes into the transmission is good, and I think the speedometer itself is good because I can reach up and spin it and the speedometer needle will move. So I thought the problem was either inside the transmission or it wasn't hooking up to the speedometer correctly on the speedometer end.


Now I'm fairly certain that the temp sender is good because we replaced it when we were doing the engine work. So I thought maybe the gauge itself was bad. I haven't gotten very far on that issue yet.


And then I haven't even hardly thought as to what could be wrong with the gas gauge, so to maybe make some headway addressing all my non-working gauges, I tried to pull the instrument cluster cover off. My Chilton's shop manual says to remove the three screws above the gauges and then one underneath, then take off the windshield wiper knob, and it should come out. But that ain't as simple as it sounds. The first three screws come out easy, but I can't seem to find one underneath. And the manual says to push the wiper knob in and turn it counterclockwise then it just pulls off, but that didn't happen. Long story short, I can't for the life of me do what seems to be the simple job of getting my instrument cluster cover off so I can see what I'm doing. I can't see much by looking up from the floor, and to twist in a position that I can look up underneath isn't the even close to what I would describe as comfortable...


And then there's the blinkers. The first time I drove it, both of them came on but didn't blink. The second time, one came on, one blinked. Third and forth times, I had no blinkers at all. And then today as I was out trying to work on this stuff, I checked the blinkers and they were both coming on but not blinking again.


Any advice for any of these problems?


One last thing: Last night driving to a little town about 20 miles away for bible study, the truck died. And I don't mean died as in stalled, I mean it was DEAD. No lights, no radio, no nothing. As if some one had removed a battery terminal. I looked around under the hood for a few minutes, then tried to start it. The warning lights came on but when I tried to turn it over everything cut out again. I started looking under the hood again and found that the electric choke wire was unplugged. So I plugged it in and it worked for the rest of the night. So my last question is, could the electric choke have shorted everything out? Or was that just a coincidence and something else caused everything to cut out? I'm fairly certain the choke was plugged in when I first started the truck, because the choke engaged.

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The outer sheath can snag on a branch or something and be stretched slightly longer than the inner cable. When this happens there isn't enough to poke out and into the speedometer on the dash end. Replace.


Clean the battery posts and the cable clamps throughly and tighten them on securely.


Check and clean the fuse box. The fuses should be held very snugly by the clips. On a vehicle this old you can spend forever checking the fuses and they are still bad. Never trust them on looks only. REPLACE them, easy and cheap and good peace of mind.


The gas and the temp gauges share a common voltage regulator so (usually) when both are not working it's the regulator. Hoping the fuse replace/cleaning has solved this problem.

If not find the Yellow/White stripe sender wire and ground to the engine with the key on. The gauge should read full scale hot. Same with the gas tank. make sure the Black wire is well grounded. If it is, ground the Yellow wire... the gas gauge should read full. If grounding the temp and gas gauge wires produce no result then it's likely in the gauge cluster in the dash. But first be sure that there is voltage on the 10 amp fuse closest you on the left side with the key on.


To get the wiper knob off pull out fully. Grip the shaft below the knob tightly with needle nose pliers as close to the dash as you can. Holding tightly, push inward on the knob and twist. It's spring loaded and will come off toward you.

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When removing the guage cluster, you also need to remove the cigarette lighter and heater control knobs. The heater knobs have a screw from the bottom of each. The cig lighter has a metal cage on the backside that unscrews. This is the one people miss or forget and end up breaking the dash bezel.


The screw from the bottom that is difficult to find is to the right(barely) of the steering column and points almost straight up. It goes into a bracket on the back the the warning light guage housing. If the vehicle has a factory tach(74 should not) then there is a matching screw pointing up from the bottom that goes to the back of the tach housing.

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NAPA can't get me the speedometer cable, or sheath. I have never heard of an instrument panel regulator, nor had my almost expert father. Nor had George, the NAPA owner (small town, you know) and he said there wasn't one in the computer. Were do I find these kind of parts?


When I went to the basketball game last night, the blinkers started magically working again...I'm perplexed.


Now, how far out does the speedometer cable need to stick out? Because there's a good 3/4 inch or so.


One thing I did accomplish, was that the positive battery cable was extremely corroded. I cleaned it, and maybe solved the electrical blackout problem.


I havn't even done anything about the fuse box yet, I spent yesterday working on my carburetor and then drove it to a basketball game. Seems I solved the fuel problem, so I am definitely making progress.

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There's a saying that most fuel problems are electrical. Cleaning the battery cables may have strengthened your ignition and it runs better now.


If idling with lights and heater on, the voltage will be down close to 12 volts. When revved up it would be just over 14 volts. The temp and gas gauges would thus read higher or lower depending on the chare from the alternator. To prevent this Nissan built a tiny voltage regulator to supply about 8 volts for the gas and temp gauges to run on. With a stable 8 volts the gauges read the same at all times. The 620 voltage regulator for the gauges is in the gauge cluster and is a small bi-metallic strip with contacts and a smaller wire wrapped around the strip. When the contacts close the wire heats up, the strip moves and opens the contacts, the wire cools and the contacts close again. It does this fast enough to regulate the flow of current through the two gauges and stabilize it.

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Yep. An almost-expert is still not a an expert.


NAPA has the 620 speedometer cable



Here's a 620 instrument panel regulator. Only worry about this if BOTH the fuel gauge and temp gauge are both having the same symptoms. Btw most cars have something like this, chevies, fords, etc.


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Thats interesting. I'll probably pull the instrument cluster tomorrow. Yes, the temp gauge and fuel gauge are having the same problem, and that is that they plain don't work.


George told me he couldn't find me a speedometer cable, and your link keeps not working.


Were do I find an instrument panel regulator? Do I have to go to Nissan to get one? How much will it cost? I ain't sure I'll need one yet, but I want to know were to find it and how much to be prepared to pay for it so I can buy one without taking time so search if I do need one.

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Yes, buy it Nissan. It is part of, and not separate from, the water temperature gauge.


Balkamp 6151682 speedometer cable. The difference between various year cable is the length. Even automatic and manual transmission use the same cable ends, just different lengths. So measure yours and it is 70" or less, this NAPA 70" cable will work for you.

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