I know that diagnosing electrical problems without seeing the installation, and what's going on is pretty hard.

However, I'm not having any luck solving the problem.

So, here goes.

We're looking at a '69 here.

I have a Covan's dash with Autometer Ultra Lite Electronic gauges and have done the headlight relay upgrade as discussed on the TC forum.

Other than that, the dash wiring is pretty much original.

Here's the problem. When I turn on my headlights, I'm seeing a short that causes my Oil pressure gauge to peg and my temperature gauge to read zero. My bright light indicator comes on, and both of my blinker indicators come on.

Where it gets interesting is that when I turn the rheostat on the headlight switch, it changes the intensity of the bright light indicator and the blinker lights. It doesn't, however, change the reading on the oil pressure gauge and the Temp gauge.

The sender wire for the Oil Pressure gauge reads around .254 OHMs with the engine off. Should this read zero with the engine off?

I have disconnected the rear harness under the dash to see if the short was in the rear. Still had the same results.

As it stands right now, my marker lights come on just by plugging in the headlight switch (with it in the off position).

I've tried a different headlight switch. Same results.

I wiggled the wires coming off of the dimmer switch and did see the bright light indicator turn off, but, I can't say that is my problem (yet).

There are most likely a ton of questions. Any help would be appreciated!

Oh, I just did the first two legs of the Power Tour (Cleveland to Racine) without any problems. On my way home from Racine (in the rain) I turned on my headlights, and saw my gauges start doing goofy stuff.

Thanks in advance for the replies.

you have a bad ground in your dash, the whole thing. Check your ground wire connection.

And I'm really bummed that I'm stuck in Texas while the PT runs right past my house, again....

Sounds like you have the ever common dash ground problem, like Jim points out, or a short in the wiring under the dash. I think it may be time to unwrap the harness and take a look, the wiggling harness points toward this (could also be a problem in the connector)

you could check the resistance between the oil press or water temp sender wire and the headlight wires, I think you will find your short there

and the oil pressure sender seems ok, 1/4 of an ohm is nothing when the gauge probably uses something like a 0-100 ohm scale

If I'm remembering correctly, that covans dash is plastic, and everything in it needs a ground wire. Assuming you daisy chained the ground and then brough it to metal, it'sa come loose right there where it goes to metal.

you could check the resistance between the oil press or water temp sender wire and the headlight wires, I think you will find your short there

Does this mean that I am looking for a zero or a one on the OHM scale?

Assuming you daisy chained the ground and then brough it to metal, it'sa come loose right there where it goes to metal.

I did daisy chain the ground. I'll check my grounds when I get home today.

I think it may be time to unwrap the harness and take a look,

I neglected to mention that I did unwrap the entire harness, checked it for any shorts (or potential shorts), and then rewrapped the harness in Scotch 33 and wire loom.

Also, I did learn from the previous forums that I had read to solder and shrink tube all connections.

I thought that I had everything covered.:sad:

Does this mean that I am looking for a zero or a one on the OHM scale?

basically yes, a very low reading. But I think the ground is more likely especially if you already unwrapped the harness

One more thing to add.

Using the Ohm meter in audio mode, when I put one probe on the negative side of the battery, and the other on any of the three terminals on the headlight, they all respond with the audio tone.

This tells me to look for a short more than a grounding problem. Correct?

One more thing to add.

Using the Ohm meter in audio mode, when I put one probe on the negative side of the battery, and the other on any of the three terminals on the headlight, they all respond with the audio tone.

This tells me to look for a short more than a grounding problem. Correct?

What youve done was check continuity. GREAT ELEC T/SHOOTER TOOL! If you touch one side to the neg and the others like you said, YES something is amiss......turn everything on and then pull one fuse at a time checking for the lights to go normal. Turn H/L's on and pull one fuse, then look, no change? reinstall fuse, pull another, etc etc etc...

WHOA!!!!!

Checking headlight, by grounding 1 probe on an ohmmeter and sticking the other into each headlight terminal is prooving nothing but that the headlights are not burned out!

One of the 3 wires IS connected directly to ground.
The other 2 are connected to ground at very low resistance by the filaments in the headlight, that's what makes them work.

Your symptom is very clearly a bad dash ground. This happens on 67-68's all the time, normally doesn't happen on 69's with stock dashes.

When the headlights are off, everything is able to pull a bit if a ground thru the dash light and turn signals, but it's flaky. Headlights on, you lose any sort of ground completely. Turn signals get weird too.

You don't have a short, shorts blow fuses and burn wires up. You have an open, an open main dash ground.

Jim,

Not the actual headlights. The wiring that plugs into the headlights. I disconnected the plug from the headlight and tested each of the terminals in the plug. Unless I am mistaken, all three of the headlight wires that plug into the headlights should not be resulting in a zero ohm reading when the other end is on the (-) side of the battery. Correct?

Am I doing the wrong thing by using the OHM meter to check to see if I have ground conditions?

I checked the ground wires that I could get to (three of them) under the dash by grounding on the door jamb switch and each of the terminals for the grounds. All of them resulted in a zero on the OHM meter.

I appreciate your responses. Thanks.

the problem with trying to chase bad grounds, or anything else with an ohmmeter is that the meter "see's" the whole circuit.

An ohmmeter is the proper tool to use to test a single componant that has been isolated. You can verify a sitch works by disconnecting it, putting the ohmmeter on the switches terminals, and working the switch and seeing a change. You can test a fuel sending unit by disconnecting it, connecting the ohmmeter, swinging the float, and seeing the reading move from zero ohms to 90.

While you can check a fuse with an ohmeter by popping it out, you can test it easier with a voltmeter with it in. If the fuse is good, it has no resistance therefore no voltage drop. Zero volts = good fuse, 12 volts = bad fuse.

You can do the same thing to find bad grounds, high resistance connections, or many other things.

Certain things should have voltage across them, such as a light that is on.

Other things should not, such as a switch that is turned on, or a connection in a wiring harness.

Note that a voltmeter reads "the difference" between the 2 points where you put the meter leads. It's relative only to that.

If you put one lead on the pos battery terminal, and the other on the big red wire on the alternator, you will read zero volts because BOTH points are at 12 volts, there is no difference.

If you put one voltmeter lead on the ground stud on yout temp gauge and the other on a good ground, I bet you see the following:

Zero volts (as it should be) when the headlights are on, and...
Several volts, maybe as much as 9, when the headlights are on!!!

Why? Because the guage isn't grounded, but... it's ground wire is shared, perhaps with the high beam indicator, or the turn signal indicators, or with some of the dash illumination bulbs (turning the rheostat, big clue there!).

And what's on the end of those bulbs? Ground, with a couple of ohms of resistance thru the filament, not enough to mess up the guage.

And what happens when you turn on the headlights? That wire that the guage was "borrowing" to reach ground goes to 12 volts, and the guage goes crazy.

With the covans dash in your car, you'll have a lot of wiring and connections that are not stock, and while I would know them if I saw them, I can't know them well from here.

Your resistance readings on the headlights do have me a lil puzzled. With the relays, the power feed to the headlight sockets should be completely isolated from everything until the relays are energized. Your readings do show a problem, but I can't be sure exactly what, particularly since you reported that everything had worked at one recent time,and then failed to work all by itself.

Thanks Jim.

I'm pulling my dash (and my hair) out to get a better look at my situation with the ground wires.

The more I dig, the more I wish that I would have bailed the stock harness and just put a complete painless harness in it to begin with.

You're right that I do have a number of connections for the gages and other accessories.

A couple more things that have come up.

The brown wire that comes off of the dimmer switch and goes to the bulkhead connector is defiantly a bad connection. If I wiggle it, I can hear my headlight relays clicking.

If I rotate my main pigtail connector for the gauges, it produces some pretty weird results. The blinker lights stay on constant until I twist it. Then the blinker lights go out and the dash lights come on (with the headlight switch off) if I twist it the other direction. There is a ground wire going throug this pigtail, so, this is what I am going to trace next.

As soon as I get the dash in a state that I can get a better look, I'll let you know what I find.

This isn't exactly wasted time. I have a Holley commander fuel injection system that I had to wire in anyway. I guess now is as good of time as any.

It might get a completely new harness yet.;)

Yeh, Jim was right. Bad ground. Problem solved.

As far as the marker lights doing goofy stuff, well :sad:, lets just say that the person that was diagnosing the problem created his own problem.

Simply put, this problem was a bad ground.

Thanks everyone.

:thumbsup::hurray::beers: