My "one feature" truck

[kopeck]

My first post so a quick hello first off.

So...my '79 1/2 ton custom deluxe is more or less a fair weather vehicle.  I very rarely drive it in the rain or even at night.  Well a few days ago I had it out on a very rainy day and found that the electrical system really didn't seem up to the task.

Any time I turned anything on, say the lights or the wipers the volt meter would drop from the center down to what I would gauge to be 10 or less volts (not exactly a precision gauge).  Having both the wipers and the lights on at the same time you really could see everything straining, the wipers wouldn't work at all on "high speed" and on the other setting were slower then normal.  Kick the blower up and things just got worse!

The last few times I did drive it at night I though the lights were pretty dim but chalked it up to being used to my newer vehicles, now I'm thinking there may be something to it.  Pretty much I can only have one thing going at a time.

Anyway, probably should start with the ground.  I see the battery is grounded on the alternator bracket but I don't see any other obvious grounding points?  I guess it could just be a tired 10SI too, even with nothing on the voltage fluctuates somewhat.  I can get my meter out and double check that though. 

Any other ideas?

Thanks,

K

[454Man]

My factory gauge is like that aswell. I hooked up my volt meter and see 13 to 14, volts

[bd]

Hello K!  Welcome to the site.   

Like 454Man suggested, begin by checking your volt gauge.

Then, in addition to checking the engine & chassis grounds, alternator function and belt tension as you suggested, check the battery condition and cable connections.  Take a peek at the fusible links off the starter and firewall junction block.  Check that all your connections are clean and tight and that none show signs of heat damage.  You might also inspect the bulkhead connector through the firewall for heat stress.  A poor connection anywhere (loose nut, poor wire crimp, weak terminal tension, etc.) in the 'feed' (high load) circuits will cause menacing loss of voltage.  If the cause isn't readily apparent, you may need to perform some voltage drop tests across the harness.  If your dash voltmeter is accurate, it sounds like you have more voltage loss than is typical or desirable.  However, some voltage loss is normal and to be expected....  Good luck!

[Fairlane514]

Simple check to see if your alternator is charging.  Use a multi tester to first test the battery to see what it  is reading with the engine off. If it reads the same with the engine running the alternator is not charging. It should read between 13.5 and 14.5 if the alternator is charging.

[kopeck]

Thanks for the reply's guys.

I'm driving the truck today so I've been paying attention to the meter and how turning things on and off effects it.

The voltage seems very RPM driven.  At idle I doubt it's making 12 volts or less, at medium speed the needle sits on 13v and higher cruising speeds it's up in the 14v range.

I don't have a tach so I can't say what she's really turning, but it's a 350 with a 3 speed.  I thought there wasn't suppose to be a lot of fluctuation with Alternators, that why they went away from generators?

Anyway, when the meter is showing 14 or so volts the wipers work as they should, high an low, at 13 volts they still work but high and low are almost the same speed and below 13 only the low speed works but that's it.  The more stuff you turn on the the voltage takes a nose dive, like light on, wipers on and the fan on medium the meter shows 10ish volts.

I haven't used my multi-meter to verify those reading yet but I hope to do so tonight or maybe tomorrow.

I do know that running it normally (ie nothing on) it does charge the battery as it never gets run down.

Thanks,

K

[kopeck]

You know, I think my issue might be as simple as a worn belt.

I can't hear it slipping, I've used some belt dressing in the past and while it quieted down the belts I'm sure it didn't help them grip.  I ran the truck a bunch over the last few days and the needle is much more stable now, at idle it sits at 13V and anything above that it's 14/15ish.

I'll pickup some belts and see what happens, they need to be replaced anyway.

K

[kopeck]

Belts seem to have made a difference.

I can turn on all my gear and have the volt meter sit right at 13 volts now.  I also verified that voltage with my muti-meter.  I'm not sure how many amps my 10SI puts out but I'm thinking it's one of the lighter versions.

Sometime its simpler then it looks.

Now I need to get it home and tighten the PS pump belt, not sure why I left it so loose but man that's annoying.

Thanks,

K