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78 620 charging problems


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Just purchased a 78 620. Truck ran fine charge light was on but dim. Truck broke down on highway and brand new mechanical pump failed. The part store did not have the right pump so I had to install an electric pump. Drove 200 miles and had to jump it every 50 miles or so.I took the battery and alternator to the store and had them tested the alt passed and the battery failed. I put everything back together wired the pump correctly. The charge light is still on. Now the issue I'm having in the alt is not making enough power at idle but if you rev it up it is good will even overcharge. If you use the lights it is not charging enough even while revving. I've cleaned all wiring and fuse block. I'm going to add grounds from battery to body and body to frame. Any thing I should check?

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...... I put everything back together wired the pump correctly. The charge light is still on. Now the issue I'm having in the alt is not making enough power at idle but if you rev it up it is good will even overcharge. If you use the lights it is not charging enough even while revving. I've cleaned all wiring and fuse block. I'm going to add grounds from battery to body and body to frame. Any thing I should check?

 

How do you know it is 'over charging' with the lights on? Do you have a volt gauge?

 

Engine off 12.6 volts

Engine on 13.8-14.5 volts charging normally.

 

Just ground battery to engine (check clean the negative battery cable to the head behind the fuel pump) and the body sheet metal.

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if it over charges then the volt reg is bad.

 

I dont know YEAR when the cross over from external volt reg to a internal type(inside alternator)

 

 

find a cig lighter battery alternator monitor that plugs in. They work really good and dont drain the battery

 

Equus makes one.  uses diodes lights

 

 

to me the alternaot works untill you put a load on it. NAPA cheaks mine and they load it down. then you can tell

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Sorry guys it is a 1978 620.

¤when the truck is at idle with no accessories on it is under charging.

¤when the trucks rpms are raised it is charging and sometimes goes into overcharging.

¤with any accessories on it is under charging even with raised rpms.

I'm using a battery/alternator tester as my multimeter is mia. So I don't know the exact voltage.

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That's definately not charging well. If it's internally regulated, take it off and have it tested on a bench tester at oreilly or auto zone or where ever. Sounds like regulator failure, as mentioned

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13.20 is a little low, especially considering you checked the voltage at the alternator.  I like to see 13.5 to 14.5 at the battery.  you lose voltage as current travels through a wire.  The more current, the greater the voltage drop.  So, if you are driving at night, headlights on, heater on, wipers on, 13.2 volts at the alternator could easily be too low to charge the battery fully.

 

I am guessing on a cold Wyoming morning, you would like the battery fully charged.

 

The general though on this forum is you are better off getting a used OEM Nissan alternator from a junkyard, than a rebuilt one from a chain auto parts store.

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The pump has a min pressure of 3 lbs and max of 5 lbs.

 

I'm picking up a new alternator at oreillys tomorrow. The truck needs to run and drive so my fiance can get back and forth to work. Hopefully that will get it on the road until I can go hunting at the salvage yard or convert to a more reliable alt. Thank you all for your help and I'll let you know if the new alternator fixes it!

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