First let me say that I don't think this is a gage issue at all.
I have just changed an engine cooling fan switch for the 4th time in the last couple of years.
59 EC---454---All new wiring and components---internal regulator--3-wire

Fans on at 229 off at 205 ----- the car cycled and the fans came on at these temps for about an hour while idleing in the drive----then out of the blue-----jumped up to 240 before they would come on and then go off at 220:wacko: (I now suspect voltage drop while idleing)

So after dinking with the timing of the engine last night (I did have running warm issues) and taking it for about a 15 mile spin the engine temp stayed right at 195----made me very happy.

This morning----40* out-- on my way to work and the silly car ran at 220 all the way to work----with the heater running. (confused as hell--pulling hair out)

This afternoon driving home from work-----195 all the way home--no heater.

So--I start playing with the heat/AC controls and this is what I find

As soon as the blower motor is turned on---temp goes up 10-15 and oil pressure drops 10-15

This is almost instant.

Now, I have suspected alternator issues for a while.
While at cruise with the headlights on---12.6 on the voltmeter---drops more on high beams---down to 11.? AND if the AC/Heat is turned on--10.6

Alternator will not consistantly provide 14.2 (recently checked and the best it would give is 12.7)

Sometimes at first startup I will get 14+ , but not very often.
(alternator is coming off tonight)

This is a standard 3-wire alt for a 79 Chev C-30/454
This should be plenty for HEI, AC, and a low amp draw fuel pump.
(internal fuel pump for an 86 Bronco--with bypass regulator)

Can someone attempt to explain to me how a voltage drop would affect the readings of the gages.
(less voltage for the resistors play with?)
(lower resistance on the temp gage is higher temps --ie: example
0ohms would be 275* ---- 100ohms may read 78*) I have no idea how the oil pressure sender is calibrated.--------and why is my fuel gage not affected???

Fuel gage remains steady----just the oil and temp that vary with the volt readings

Anyway---now pretty confident that the car was NOT running warm early this morning.

Bryan, strongly suggest you start by checking out this site: www.madelectrical.com and in particular, their tech section-has VERY good explanations of how our charging & power distribution systems work. 1st item is to get your 'sense' lead near the heaviest load. Good luck!

http://www.madelectrical.com/electrical-tech.shtml

I'm wired up correctly (except the sense wire is jumped to the alt output--kit came that way)
And no matter what the car voltmeter reads----a handheld reads exatly the same at any given point in the system. Fusebox on any buss, junction on firewall, alt. output or battery. Running or not handheld and and the gage read the SAME.
Pretty positive at this point there is an alternator issue.
At this moment----11.6 key on-car off fuel pump on------turn off pump and get 11.8 (should have 12.6+ engine off)

No question that I have a charging issue----but has been doing this for well over a year.

I'm just wondering why it would affect the gages the way it does.

(just for 'sport & amusement' I will run a (16ga?) 'sense wire' to my fusebox to see what happens when I take it for a spin)
The alt. feed wires and the fuse box buss feeds are all #8 wire. I'm not sure I would ge a noticable voltage drop with this wire.

My power disitribution is:
Battery cable to starter----#8 wire from starter to firewall junction.
#8 from Alt. to firewall junction.
#8 from firewall junction feeding ignition switch and fusebox.

Curious as to what handheld are you using? Some inexpensive voltmeters might not read very accurately. You should see .2-.5 volt difference measuring around your wiring harness (alt output to say, headlight leads). Definitely should see a change between running and off. If you meter shows them all the same, the meter's not sensative enough.

Also-your wire to the starter is a #8? Or is that a typo? I'd expect a #0 or higher for the main starter power. I'd be very suprised a #8 could carry the current to start a motor.

From what I understand, if you put the 'sense' wire (I'd go 14 gauge for lower loss) to a main junction point where your gauges are getting their voltage reading (fusebox?) that should 'up' your alternator output. Some real good reading on the MAD site.

Also-your wire to the starter is a #8? Or is that a typo? I'd expect a #0 or higher for the main starter power. I'd be very suprised a #8 could carry the current to start a motor.

^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^

Naaaah----#0 battery cable to starter----sorry:D

The only difference between my wiring and the Mad diagram is that I have no normal horn relay to use as a junction.
Headlights--Horns--Cooling fans are powered with a run directly from the battery thru Bosch relays Mounted where orig horn relay would be.

I have pretty much read that entire Mad site.
(did I retain any of it---dunno---will be determined at a later date;))
I did a LOT of thinking and reading before wiring the car.
Headlamps are on relays
Fans and fuel pump are on relays.
The only high draw item the in the cabin is heater/AC unit.
Everything else is low draw relay operators.

Well-----Happy New Year:beers:
I am off to go play with the car some more---headaches to follow, I'm sure:D. Need Coffee Now:wacko:

Bryan

:)Update just this morning

Got a new alternator----had battery tested.
Install new alt.
(just fer chits&giggles I created a temporary jumper to sense farther away from the alternator) I have a constant hot fuseblock on each side of the cowl fused for the door solenoids and remote windows, so that I can have access to the electrical in case of remote or fuse failure for the doors.

I hooked the temporary sense wire to this block, with about 8ft of 14ga. This block is technically farther away from the alt. than the fuse box is.

Fire up car----14.8vdc-----dropped to 14.6 after about 3 minutes
(batterey a bit undercharged at this point)

Run the car up to temp----(Found out my choke lead had a blown fuse and would not come off the last high idle step-----maybe that's why I can only get 13mpg)

Remember---cooling fans originally came on at an indicated 229*
and when I operated the heater blower----indicated 240+*
Oil pres went from 40 to 30 with the blower on.

(I neglected to mention that the moring I took the car to work, and thought it was running warm---I also felt a "lean surge" sensation that I did not get later in the day without the headlights or heater running---I now assume it was the HEI cutting out due to a voltage drop)

NOW----fans kick on at an indicated 220----off at 200:yes:
oil pressure is also reading 45 at 2100rpm----warm engine

Volt gage reading 14.6

This part made me happy-----
turn on headlights----High beam
turn on AC---fan high
Engine cooling fans will come on with AC high pressure
Turn on stereo--------actually sounds much better now too:cool:
Could not get the gage to go lower than 14.2vdc

So now I remove the temporary sense wire---(not to keen on running new wires just yet:noway:)
Volt gage 14.1
with lights, AC, stereo, cooling fans running
Volt gage 13.7
@ 750rpm

This is all much better than the 2-3vdc drop I was getting with the other alternator----that actually tested good.


Gonna go on a test flight here soon to see if it will maintain these readings.

Oh----still not understanding the 'mechanics' of why the gages were reading so funky.
(have a therory----but not sure)
Think this might be a query for an electronics guru???

I'm not an electrical guy by any means, so take this with a grain of salt - but it seems to me that you're only attacking this from the power side, and not from the grounding side. I'd check that you have good ground connections, where they are supposed to be, and good frame/engine/body grounds as well.

All of the grounds were good.
There is no ground connection in this car that does not gove a '000' reading on the meter. This includes the ground buss under the dash that virtually everything is grounded to. My readings are all '000' from the buss, to the battery or to the body, or to the engine, or frame.
Temperature switches read "000" from the body of the switch to the intake, to the frame, and battery.

Well----test flight went good
get to cruising at 70+ in 4th (3k+rpm)

engine temp stays @ 180 (180 hi flo stat with relief hole)
Oil pressure up to 60

Volt gage reads steady 14.2

Drops to 13.8 with ALL accessories going
(lights on high-AC-cooling fans-stereo-fuel pump)

Could be all this time I was fighting an overheating issue that NEVER existed.

I mess with stuff at work that is sensitive to .1vdc.
So I do have some grasp of the supply/return thing going on

But his silly car has regularly run down to 11vdc and was not giving me any starting issues at all-------Avg batt voltage without it running had been right at 11vdc

I will venture to guess that the electronics in the Digital gages are WAAAAAY more sensitive to supply voltage than anything installed in most cars OEM.

(pretty sure I read that my fans, stereo, and gage control box really want 14 to operate efficiently----just figgered 12ish was okay-------doubt I'll make that mistake again.)

I think I will send some of these notes to a tech @ DD, see if they have any input.

(sorry about the long winded posts----just did not want to leave any holes)
Most queries are short of some vital info. Hope this was not