Ford Pickup.. Slight update

Hey guys,

So last night, I posted about my "pulsating lights" on my 86 pickup.

Today I tightened up the alt belt a little (not to the point of slipping, as the vac. pump runs off the alternator, and I maintain a good vacuum) but it was a touch loose.

I removed the regulator, and found one post was corroded/rusty, so I cleaned that up, as well as the grounding surface.

I checked grounds, and all seem ok (using multi-tester with one lead on - batt post, probed around with other lead, and all but one showed no resistance, replaced the bad one, then it checked out ok also) I checked the ALT. case and reg. case also.. show to be grounded ok.

What I have decided is this: when the truck is first started (after cranking/glow plugs cycling, etc.) it don't seem to be as bad.. As it will use the voltage to charge. Once the batteries are "charged" it starts to do it noticeably. On a digital voltmeter, it will peak about 14.9 volts, then drop to 13.9-14.1 range within 10-20 seconds, then repeat.

It's hard to say, as a lot of this is "visual" but driving it tonight about dark, it seemed as all the attempts helped some.. but the meter was showing about the same thing I saw last night.

I did a no load and load test per my Chilton's manual, and everything checks out ok there (aside the voltage being "high" at it's peak)

I went to pick up a regulator tonight, but forgetting it was Sunday, the store was closed when I arrived.. Never thought to ask how late they were open, and here I was thinking it was Saturday still.. OOPS

Hoping to get a regulator tomorrow and see if it fixes it.

Brad

It's unlikely you're going to be able to detect a bad ground on the "ohms" scale. You need to measure VOLTAGE with the engine running. Measure the voltage drop from the alternator case and regulator case to the battery's negative terminal. Do the same from the alternator output and regulator sense lead to the battery's positive terminal. If the alternator is charging at ten amps, a 100 milliohm resistance will produce a 1 volt voltage drop. You simply can't measure resistances of less than an ohm with a typical multimeter on the ohms scale.

Mark,

Could you please explain a little more on how I would check voltage as you recommend?

When I try checking voltage from the case of alt. or reg. I get nothing.. Am I doing it incorrectly perhaps? I set my digital multi-tester to V-DC 20 and hold the black (negative) to the battery - terminal and probe the cases with the other and show nothing.. Am I using the wrong setting perhaps? Yes, I did this with the truck running.

I know I'm charging, the voltmeter shows that.. At what rate, I am not sure.. Trying to track down what makes the lights pulsate, and I hate to just throw parts at it.. Sure, it might fix it, or it might not..

I can wire stuff up to make it work, but when it comes to troubleshooting electrical, I'm not too good, but trying to learn.. I'd rather know how to troubleshoot so next time I have a issue I know what to do.

Thanks,

Brad

Brad, when measuring voltage drop, "nothing" is good. You do need to make sure you're getting a good contact with your probes, which should be obvious as the meter display will settle down when your probes make contact. If there's no voltage drop, then the meter should show only a few millivolts.

If you can get the lights to pulsate at idle, I'd check the positive voltage at different points: the battery, the alternator and the lights themselves. Always use the same ground, preferably the negative battery post. I expect you'll see the voltage fluctuation everywhere, but if you don't it will give you a clue where to look. If you DON'T see any voltage fluctuation, the the problem isn't in the charging system; more likely a bad lighting ground.

My old vom has 4 divisions on 0 to 1 on the ohms scale.I can tell if an scr or a diode in paralell is shorted.Needle point test prods make a difference.Bought the meter in 1951, still use it.

Mark,

Thanks for the reply.. I think I figured out what you mean by voltage drop..

It just now come to me.. I was checking with both leads of meter to ground, and it would show 0.. But what you're implying is to keep one on the "hot side" of the battery, and "rotate" grounds from the battery to the reg. case to the alt. case and take notice of the voltage.. Right?? (Sorry, sometimes I have a "lapse of brain function" )

As for the pulsating, I show voltage fluctuations at the battery (once charged from starting) as well as it shows up in the amp gauge in the dash.. Using the meter I have it will slowly climb from "start voltage" 12.5 +/- right after the truck fires (depends on glow plug cycling, cranking time, cold start, etc.) and will work it's way up to about 14.7 or so, then will drop to 14.0 +/- like the regulator kicks out, then kicks back in.. and it will then just repeat itself from the high 13's to the high 14's

The only reason I don't just change the regulator is I was advised that the "solid state" regulator shouldn't do this, so I am looking to exhaust all other possibilities first, but it really seems to me like the regulator is failing to function properly. It never bothered prior to a prolonged parked period (I used to drive it almost everyday, but it has went less than 150 miles since April, well up till the other night)

Brad