Wiring Question/Translation

[jmcgill89]

I've been looking at the wiring diagram and trying to translate everything to the connector for my printed circuit.

When I take a Volt/Ohm meter to the connector with the key in the "on" position, I get power from a couple of the wires, but not all of them. For instance, when I turn the lights on, I get power to the light blue/red wire. I also seem to get power to the thick red and black wires there...but nothing else.

I'm trying to decide whether my printed circuit is shot or whether I have some sort of wiring issue.

 

[don29163]

might help if you tell us what is not working and the year

 

[jmcgill89]

Oh, sorry.

It's a 1973, and I have the idiot light cluster. Nothing left of the fuel gauge has any power. All bulbs are good.

might help if you tell us what is not working and the year

 

[rvrtrash]

If you need to see if the printed circuit is good, you can use your voltmeter (ohms setting, wiring connector unplugged) to measure from the plug contact point to the contact points for the lights. You can visually trace the "wires" to see which points to check, and look for breaks at the same time. If the printed circuit is good, you know the problem is elsewhere.

Steve

 

[midlife]

Ahhhh...a question I can offer advice to!

To test the circuit card, remove the cluster plug, and use your DVM on resistance, and measure continuity between the cluster flap pin and where the circuit trace ends up at. You should see 1 ohm or thereabouts (actually about 0.2 ohms).

If all that is good, then the circuit card is good, so the next step is to see if you're getting the right voltage to the cluster pin at the right time. Some pins work all the times, others only on ACC or RUN, others only on RUN, and still others work off of the headlight switch.

Typically, I've found that the pins on the dash cluster connector often have high resistance, due to poor factory crimping or that the wires are not making enough contact with the crimp. You should try and keep the wires straight as you can when they approach the crimp.

The red wire is an ammeter lead, and that should always be hot. The black wire you're talking about is probably the ACC line to the constant voltage regulator.

 

[jmcgill89]

Thanks for the input.

I measured the resistance on everything on the printed circuit, and didn't find any problems. Specifically, for the cluster lights, I had no resistance from any of the light sockets. AND, I have power for the cluster lights (light blue wire) at the connector when the lights are on. That being said, the last of my das lights (on the right side) stopped working last night.

So now, I have no dash lights, AND no idiot lights. There is power going into the printed circuit, because the fuel gauge still works.

This is VERY frustrating. I was reading that there was a ground over by the turn signal flasher that sometimes corrodes or comes loose....I may check that.

Ahhhh...a question I can offer advice to!

To test the circuit card, remove the cluster plug, and use your DVM on resistance, and measure continuity between the cluster flap pin and where the circuit trace ends up at. You should see 1 ohm or thereabouts (actually about 0.2 ohms).

If all that is good, then the circuit card is good, so the next step is to see if you're getting the right voltage to the cluster pin at the right time. Some pins work all the times, others only on ACC or RUN, others only on RUN, and still others work off of the headlight switch.

Typically, I've found that the pins on the dash cluster connector often have high resistance, due to poor factory crimping or that the wires are not making enough contact with the crimp. You should try and keep the wires straight as you can when they approach the crimp.

The red wire is an ammeter lead, and that should always be hot. The black wire you're talking about is probably the ACC line to the constant voltage regulator.

 

[gsmaggot]

My pc board needed to be replaced due to blown traces. I took and cleaned every terminal on the plug with a pencil eraser and then also bent the tabs out a hair so the plug made a tight fit. also i needed to do the same on each light, cleaned and bent. The dash is back to 100%

 

[Don C]

The light blue/red wire is the wire for the dash lights, the red wire (with yellow hash) provides 12 volts to the hot side of the constant voltage unit (which feeds the hot side of the fuel gauge) and idiot lights. The black wire provides the ground for the dash lights and the constant voltage unit.

The ground side of the alternator light is the light green/red, the oil pressure is the white/red stripe, the temperature is the red/white stripe, and the brake warning light is the purple/white.

When you test for voltage on the dash light circuit make sure the lights are on and the light switch knob is turned to full bright (clockwise).

If you find a broken trace, and you're careful, you should be able to bridge the break with solder or a small piece of copper wire. Carefully scrape the coating off, without scraping through the copper trace. Use liquid tape to insulate the repaired area.

 

[midlife]

When you loose ground on half of a circuit board, that suggests to me that either (1) there are two separate traces for the dash lights or that a trace broke somewhere along the circuit, or (2) the ground plane has a similar problem.

Most folks focus upon the signal side of things when there's an electrical issue, but the grounding side is equally important. Somehow them electrons have to find a way to go back home...

Idiot lights can be tricky; sometimes you need to run the car and deliberately cause a fault to show the light; other times they come on briefly as soon as the key is turned from OFF to RUN. And then again, a bulb can be blown...

 

[Don C]

Because the idiot lights receive 12 volts from the printed circuit, all you have to do is ground the other end when the ignition switch is in the run position. Pull the wire off the oil pressure switch, temperature switch, and/or dual brake switch and ground it. For the alternator light, pull the the connector off the regulator, and run a jumper wire from the light green/red wire terminal to ground. And, like you said, make sure the bulbs are all good, not always possible to tell just by looking, use an ohm meter to check them.

 

[midlife]

Now that's good advice! Most idiot lights I work with are pre-circuit boards, and I just check for wire continuity directly.

 

[jmcgill89]

Well,

I put a new printed circuit in there and I now have dash lights....but surprisingly not all of them. Speedo is good, and the right side of the idiot cluster is good. Still don't have turn signal lights and/or idiot lights.

I give up. I'm going to run new wires and put a temp and oil pressure gauge in there...at least I'll have an idea of the condition of the engine.

I had 12v to the red wire with yellow hashes, and the light blue/red wire. However, I have no idiot lights. Maybe my connector is bad.

I'll try again to pull it out and bend things back into place.

Now that's good advice! Most idiot lights I work with are pre-circuit boards, and I just check for wire continuity directly.

 

[marks73]

Great post with good info sorry I missed it earlier. :goodpost:

 

[72fastback]

good call on getting the temp and oil pressure gauge. Most of the times when the idiot lights do work when they light up it's to late.

 

[jmcgill89]

I honestly don't know what's wrong with it. I have power at the connector and the dash lights now work for the most part.

I don't much care if the idiot lights don't work, as I'm going to put gauges in there. It's the lack of turn signal indicators that bother me now.

One of the previous owners did some bad stuff to the wiring. He didn't like the buzzers, so he removed the ones for the keys and lights and took out the fuse for the seat belt buzzer. I think he did some serious damage to the wiring.

good call on getting the temp and oil pressure gauge. Most of the times when the idiot lights do work when they light up it's to late.

 

[harrisrf]

There is a ground that attaches to the igniton switch . that is for the dash lights. on my 73 someone had broken a bolt off that holds the swich on and lost everything to the cluster.

 

[jmcgill89]

Oh, and I'm sure there are major resistance issues in the wiring.

When I'm sitting there with the lights on and the key in "run" position, the turn signals won't even work....when I turn the lights off, they work, but slowly, and the alt light and dome light dim noticably with each click of the flasher.

In addition to that, the flasher relay and the turn signal unit are just hanging there under the dash pad on the passenger side. They're wrapped in old carpet and electrical tape....Obviously the PO was a professional electrician.

One of these days I'm going to have to have a real professional look at the wiring.

 

[trainey]

Oh, and I'm sure there are major resistance issues in the wiring.

When I'm sitting there with the lights on and the key in "run" position, the turn signals won't even work....when I turn the lights off, they work, but slowly, and the alt light and dome light dim noticably with each click of the flasher.

In addition to that, the flasher relay and the turn signal unit are just hanging there under the dash pad on the passenger side. They're wrapped in old carpet and electrical tape....Obviously the PO was a professional electrician.

One of these days I'm going to have to have a real professional look at the wiring.

Just as a word of caution! If you think you have wiring issues, and you park this car indoors, it would be a good idea to unhook the battery in order to prevent a fire...my grandfather lost a garage and a car because of that once.

 

[jmcgill89]

I actually do that already.

Oh, and I'm sure there are major resistance issues in the wiring.

When I'm sitting there with the lights on and the key in "run" position, the turn signals won't even work....when I turn the lights off, they work, but slowly, and the alt light and dome light dim noticably with each click of the flasher.

In addition to that, the flasher relay and the turn signal unit are just hanging there under the dash pad on the passenger side. They're wrapped in old carpet and electrical tape....Obviously the PO was a professional electrician.

One of these days I'm going to have to have a real professional look at the wiring.

Just as a word of caution! If you think you have wiring issues, and you park this car indoors, it would be a good idea to unhook the battery in order to prevent a fire...my grandfather lost a garage and a car because of that once.