Hello all, new 720 owner. Need advice, weird electrical issues.

[Kegomatix]

Just bought an 85 720 from my dad for $250. Pretty solid truck overall, biggest issue was that he severely neglected the maintenance. In the 4 years that he owned it, he did NOTHING, and yes, that includes oil changes. But it also never gave him any troubles at all. Never broke down and was incredibly reliable. I drove it the half hour home, problem free. The thing drives and shifts like new, no issues.

 

Well, then I did the maintenance that it has needed for so long. Changed the oil, new valve cover gasket (old one was leaking) plugs, wires, cap and rotor. Fuel filter and air filter (had been running for who knows how long without one). Rear diff fluid, serviced the transmission, changed out brake fluid and clutch fluid. Flushed the radiator (and it reeeally needed it) and filled up with antifreeze. I think that's all.

 

So bear with me, kind of a long story but I feel everything should be included to help me troubleshoot. After all the work I go to fire it up, thinking that it is going to run even better from all the much needed love. It fires right up and sounds better than ever. About 45 seconds in, it starts stumbling and eventually dies. Wouldn't start back up, verified it had spark so I go to check for fuel and of course, it's not getting fuel anymore. After some research I find that the fuel pump relay is a common problem and seemed to fit my symptoms so I buy a new one, and it works.. Sort of. So I go through all the ground connections from battery to fuel pump and clean them up good, that works and the truck runs again. 

 

It's running, and it seems to be running great. Only problem is now my battery light is on, fuel and temp gauges stopped working, and my turn signals don't work. WTF?! Another day of trying to figure this out, I unhook the negative on the battery while it is running just to see if the alternator was putting out enough charge to keep the system running. It is, with no issues, so I hook it back up. Voila! The gauges started working again! Everything seems normal, until I try the turn signals. Everything died again. Disconnect the negative and reconnect then all is well again. I even took it down the road and was able to use the signals. Get back home and park it for a while then go back to try again, and they're not working. Disconnect and reconnect, didn't do the trick this time...

 

I am so confused by this! I've gone through every connection and they all look pretty free of corrosion. I am missing the fuse box cover so I don't know what fuse is for what. I have tried researching this issue but haven't found anything similar to what I'm experiencing. Sorry for the long post, I hope somebody has time to skim through it and help me out. Thanks in advance.

[Kegomatix]

Oh, and because it's my first post, here's the beauty right here...

 

 

And then my usual daily driver, that prompted me to buy the little gas saver.

 

I'm no stranger to Datsun/Nissan, have literally owned dozens of them. Just a stranger to the pickups.

[wayno]

Check the fusible links and there connections, they are the wires with the plugs coming off the positive side of the battery.

This is what it looks like, or it should look sorta like this.

You need to check the wires in it and make sure they are still good, otherwise all sorts of weird shit happens.

Here is another photo of the location of mine on the battery.

[Kegomatix]

Sorry, I forgot to mention that I disconnected each of those and made sure as best I could that all the contact points were cleaned up. Clipped them back together firmly and they seem to be good.

[Kegomatix]

Oh yea also forgot that when I fire it up, at first the battery light doesn't come on. Temp gauge fuel gauge and blinkers or still in-op. As soon as I give it a little gas the battery light comes on. It gets brighter the higher the RPM. 

 

First fired up with the battery light off the alternators output is 12.5V. When I rev it a little and the battery light comes on it jumps to 14.5V and remains there until I shut it off. 

 

Is it over-charging? I understand that 15V + could mean the voltage regulator went out. So I'm not sure if 14.5V is correct or too high.

[wayno]

Sorry, I forgot to mention that I disconnected each of those and made sure as best I could that all the contact points were cleaned up. Clipped them back together firmly and they seem to be good.

 

You need to use a volt meter to make sure they all have power when stuff stops working, these wires have ways of back feeding when they go bad, they will feel soft and rubbery without any hard wire inside of them when blown.

I have had issues in the past with these wires and there connections, I believe that when I shut off the truck when I started having issues, I would check these wires with a volt meter and find no power.

You said you had them apart, before you took them apart, did you have any issues you are having now?

[Kegomatix]

No I started having the issues first, then took them apart. This truck ran without any issues until I did some regular maintenance to it. Thanks for the help, I'm gonna go check them right now.

[Kegomatix]

Checked all the connections, everything seems to be fine and there is continuous power throughout. 

 

Now, I sat down in the drivers seat, and maybe in a bit of frustration smacked the fuse block a few times. Battery light turned off and my gauges started working again. Tried the blinkers again, and I can hear the blink a couple times, and it the battery light starts to flash. Then the gauges die again. There has to be a short or bad connection somewhere tied in with the turn signals. Any idea where I can start there?

[Telkwa]

I'm new to this forum, but I know datzenmike has specifically mentioned that these trucks have several grounds, and they all need to be solid.  I believe he mentioned that each sub-system has its own grounds.  I'd noticed ground wires all over the place on mine.  I used to think that if half of them rotted away there'd still be too many.  I don't think that any more.

 

Do you have any reason to believe mice have had their way with the truck? 

 

I had a weird electrical drain that is now fixed.  I think so anyway.  I put a voltmeter in between the positive battery terminal and the cable.  I've got some long test leads, so was able to bring the voltmeter inside the cab.  I put fuses back in one at a time, waiting to see which circuit was pulling power.  At first I left each fuse in as I went along, but I got better results by inserting the fuse, checking the multimeter, then taking that fuse back out and going on to the next one.  That process may or may not help you out.  If you have a short, it may help point you in the right direction.  If it's a broken wire probably not.

 

I'm curious to hear how giving the truck some much-needed attention initiated some weird electrical glitch. :confused:  

[Kegomatix]

I figured it out, it was the fuse block. I unscrewed it and just by moving it around some everything started working again on and off. Got it in a perfect spot then screwed it back down and everything has worked ever since. I still need to go through all the wiring down there, I might have a chance this weekend because obviously there is a loose connection or some corrosion causing a bad connection.

 

Been driving it around no issues, just got my first gas mileage estimate and this is all in town/back roads driving and it got me 25 mpg. Not sure how these trucks are supposed to do but I'm really happy with that. I'm used to getting about 13-15.

[Telkwa]

Yeah, it'd probably be a good idea to figure out what exactly is wrong.  It'd be a drag to have a cabin fire.