Need Help Finding Ground.

[derek7871]

1968 F-100, 360, 3 on the tree, 2WD.

Apparently I have a pretty bad ground somewhere on the truck that just started showing up. I have disconnected the negative battery cable and put my voltmeter on the negative battery post and the disconnected negative battery cable and it shows a full 12v. As I understand it, the meter should read 0 while doing this.

I have an aftermarket volt meter in the cab and, up until now, it always showed a nice steady 14v while the truck was running. Now, it jumps about 2v at a time up and down and the volt meter is reading closer to 9-10v when the truck is running. It looks like the ground comes and goes instead of being a steady draw. Like when the turn signal is on.

The battery is only 6 months old, and the alternator is about 5 years old. A few days ago I put a new voltage regulator on and it did not help. I plan on having the alternator and battery tested tomorrow. But.....the ground is still there.

When I had the negative cable disconnected, I pulled the fuses one at a time on that little fuse panel under the dash above the gas and brake pedals. The 12v draw was still there. Then, I unplugged all wiring connections that I could find under the dash one at a time and the 12v draw was still present.

So, how can I go about narrowing down my search to find the ground. I'm guessing there is a wire that has gotten the covering rubbed off and is resting on something metal. Occasionally, everything works OK and the voltmeter show 14v when the truck is running.

The truck does have the factory overdrive unit (that does not work ).

Sorry for the super long post, but I wanted to give as much info as I could. So, what is the best way to narrow down my search?

Cooter

[fordman]

well i think what we may be talking about is a draw on the system and not necessarily a loose or bad ground. the grounds are

battery cable to engine
engine to firewall.
there is a ground on the core support behind the headlights on both sides.
there is a ground wire behind the instrument cluster to the dash support bracket. the tail light housings ground to the bed which grounds to the frame.
there is a ground on the heater motor.
there is a ground from the laternator to the regulator on soem wiring hanresses of these trucks. that depnds on if you have dummy lights instead of full gauges. or maybe its the other way around.

other things to look at maybe the inside of each bulb. to see if the element has burned out and is crossing over to the other element in the 1157 dual element bulbs. check the wires on the headlight switch plug and the ignition switch plug. those sometimes melt. the red wire coming from the starter relay on th einner fender goes to the ignition switch. that wire could get melted. look for aftermarket radio wiring some kid has wired in wrong. or loose. you can chheck the resistor wire and the wire around it. and maybe also the brown wire coming from the starter relay to the coil. i seen one of those burn up before.

i may have missed some other grounding points. but checking with the wiring diagrams may also show those.

oh one more. if you have a 70-72 bed. the side marker lights ground to the bed. with a short black wire and small screw. you can also look up under the rear of the bed for old mangled trailer wiring harnesses too.

[derek7871]

Thanks Fordman. I've checked some of the things on your list, but there's a bunch that I have not. That will keep me busy for a little while. Thanks!!!

Cooter

[Thunderfoot]

From your symptom descriptions your problem is the alternator, sounds like some of the diodes have gone bad in it, when this happens it can cause a drain on the battery through the alternator, this will also show up as a jumping voltage as that diode is not doing its job making DC voltage.
You can confirm the drain by unhooking the BAT wire off he back of the alternator, just be sure that wire doesn't touch anything with the battery hooked up!

[derek7871]

The alternator tested bad at the parts store. When the rain quits, I am going to change it out. I'l post the results. Thanks!

[derek7871]

When I was removing the old alternator, I found the problem. The ground wire going from the alternator to the engine block was in terrible shape. The end at the alternator had the wire pulled out of the circle wire connector and the wire itself was missing about half of the insulation and a bunch of bare wire was showing. So, problem solved......right? Wrong. I decided to go ahead and install the new alternator since I had it already. However, I can't seem to get the stupid alternator attached properly. I remember I had this same problem 5 years ago when I put the old one on. I can't figure out how the stupid thing sits on the engine. I really feel like a knuckle head and I would really appreciate some advice or a picture of an alternator installed on a 360. I do remember that there was a certain way to set it in there where the 2 long bolts go through the alternator and into the block.

Cooter

[fordman]

the long bolt goes through the long part of tha alternator and through the spacer and then into the head. then the small bolt will go through the adjuster bracket and into the alternators threaded hole.

[derek7871]

I have 3 bolts. 2 long ones that go through the alternator and into the head, and the one shorter one that goes into the threaded hole in the alternator to adjust belt tension. I remember going through this when I replaced the alternator a few years ago. I feel like a retard.....

Cooter

[derek7871]

Does anyone have a picture of an alternator installed on a 360 that they can post.

Cooter

[fordman]

there are only two botls that hold the alternator to the engine and bracket. the bracket bolts to the water pump. here is a picture of a 302 alternator bracket. it is the same basic way our alternators bolt onto a 360. if yours is a three bolt deal i have never seen one. unless you have factory air. then the alternator bracket will look like this. but i dont think it uses three botls. with two of them going into the head. the third picture is of my 68 with factory air. the long bolt is on top and the alt sits low. the small bolt goes on the bottom adjuster bracket.

do you have a picture of your alternator or bracket?

[Thunderfoot]

The Ford alternators for are truck is a 2 bolt mounting alternator, if you have a 3 bolt you have something different and we would need pics of what you have.

This is a pic of the stock alternator.


These are pics of the stock mounting of the ford FE motor mounts for the alternator.

[derek7871]

That picture of the new alternator looks just like the one I removed and the new on that I have. One difference I see in the engine picture, is that mine has the bracket on the bottom that allows the alternator to swing to tighten the belts. In the picture it looks like it is on the top. What I have will work, I've just got to get over my brain fart and get it right. When I get home, I'll make some pictures of the mounting brackets and bolts.

Cooter

[fordman]

here is the factory a/c intergal air alternator bracket set up. the adjuster is on the bottom. http://www.fordification.com/tech/image ... tegral.jpg

here is a picture of the 302 with a thermactor. this could be the same if you had the thermactor. but i have never seen a 360 with a thermactor. maybe it was a california thing. http://www.fordification.com/tech/image ... 302-01.jpg

[derek7871]

Well I finally worked through my brain fart. There is 1 long bolt that goes through the alternator. The other long bolt is apparently just a support or reinforcrment for the alternator bracket. Then, there is the bolt at the bottom of the alternator that is used to swing the alternator out to tighten the belt. Sorry for the dumb questions....maybe the next time I have to replace the alternator I will remember this. Best of all, the truck fired right up and gave me a good steady 13.5v. Thanks to all!!!

Cooter