Wiring question

Mike

Lifetime Supporter
I'll start by saying I am novice at best with an ohmmeter. As I button up things I am confused by finding that with the key in the run position, I am finding ~20 ohms resistance between battery positive cable and chassis. Battery is not installed. Alternator is not hooked up. It is not 0 like a short but still what would lead to any continuity?

I took a lot of pictures and taped several wires. Unbelievably, I did not indicate keyed powered to ignition. I thought red/yellow was keyed ignition? Ohmmeter seems to confirm this. The black/green has no continuity with chassis or positive cable which makes me thing it was tach pickup and with new speed hut tach, that wire is no longer connected under the dash.

I would like to order the wiring diagram just wondering if it would help clarify as well? Seems like harness was all handbuilt as car was assembled so coloring across splices is a crap shoot it would seem. Thanks for any help.
 

Attachments

  • IMG_2055.jpg
    IMG_2055.jpg
    134.8 KB · Views: 291

Mike

Lifetime Supporter
I will do that Rick.

Does anyone have thoughts on positive cable to chassis continuity with key in run position?
 

Mike

Lifetime Supporter
Fuel pump is off. There is no battery. This is most likely just my lack of understanding of basic principles. If the battery was in there and they key was in the run position, the fuel pump, gauges, and various other components would be powered up. I was hoping someone could confirm if some continuity between positive side and chassis ground would be expected in that scenario.
 

Ian Anderson

Lifetime Supporter
Mike

Leaking back through one of the relays?

I would start having meter connected, and remove each fuse one at a time and see if one circuit causes the gauge to move, after that I would do the same and remove each relay in turn and again check the meter each time

Ian
 
You do not need a battery to measure resistance... Ian is right on the money with the fuse/ relay removal... This will narrow it down to the cause of the draw.
 
Red/Yellow wire is related to horn...
Black/Green wire is related to Tach Signal or Blower Switch.
That took 30 seconds to determine on Wiring Diagram.... Happy to help.
Are all your bulbs in their sockets?
Switches all in off position?
Pull your fuses one at a time and watch your meter...
If that doesn't work, pull all your fuses and replace them one at a time while watching your meter.

Amazon.com search
"ESI 305M 30 Amp Fuse Buddy Mini Tester"
Never leave home without one in your pocket.

Always happy to help if you find a dangling wire somewhere guys... just post a note here.
Blas
 
Last edited:
Hi,
The wiper park relay is powered thru fuse 11 and is hot if the wipers are parked with the key-on. SPF choose to use a common 3 position switch rather than a wiper specific switch then they added a relay to enable a park function. This relay is behind the small dash access hatch to the left of the steering wheel (on a left hand drive). You really need a wiring diagram from Blas.

Here is how it all works.
Steve
26823017645_5b1a263003_z.jpg
[/url]SPF GT40 Wiper Washer by Steven White, on Flickr[/IMG]
 

Mike

Lifetime Supporter
Thanks everyone! I will definitely get the diagram from Blaz. PM sent.

Let me asked maybe a silly head in the sand question. I have not done anything to the wiring of the car during this maintenance/modification cycle. The things done were to switch out the ammeter to a voltmeter. This involved splicing the ammeter wire together and then providing 12v feed to voltmeter (Speedhut unit). The other changes were to wire in the rest of the new Speedhut gauges to the existing power source and ground and dimmer that I had already successfully done for the GPS speedo. I am fairly certain I have done nothing to create a short and the ohmmeter check doesn't seem to indicate a short. All I need to finish up is supply keyed 12v power to coil.

I'm not completely opposed to going through a significant debugging process if this continuity as early described is a critical defect that needs addressing. I have not had any issues to this point with draining the battery or anything else. Am I messing up by assuming things are now as they always were and putting it back together as is?

Thanks again everyone! Good to have such a great resource.
 
your first post stated you have resistance with the key in the run position.. anything that gets power with the key on will cause resistance.. isn't this normal? Do you have resistance with the key off?
 
Last edited:
your first post stated you have resistance with the key in the run position.. anything that gets power with the key on will cause resistance.. isn't this normal? Do you have resistance with the key off?

Was thinking the same thing myself last night, the MSD for example will have resistance in its circuit under that condition.
 
Low oil pressure light will also be showing as a loaded circuit (ignition on, motor not running).
With the ignition off it should have at least 1M ohm (open circuit).
Cheers, Gus.
 

Mike

Lifetime Supporter
your first post stated you have resistance with the key in the run position.. anything that gets power with the key on will cause resistance.. isn't this normal? Do you have resistance with the key off?

With key off there is no continuity with chassis ground from positive cable. I checked the wiring on the new gauges and there is 20 ohms across positive to ground. I don't think there is a problem. I'll know soon enough.
 
Its can be going to ground through light bulbs guys as they are always grounded,eg ign lamps.

Forget the ohms meter this is a better method.

I use a stop lamp or head lamp bulb as you need load 5watts at least.

If testing one circuit only remove the fuse and put the bulb across the fuse.
So you get an understanding the bulb requires 12v and ground to light up.
On one side of the fuse it has 12v if it has a short to ground it will light the bulb when you connect to the other side of the fuse.
You can do this across a fuse on a particular circuit or across the battery doing the whole system.
If you do the hole system you must disconnect all the light bulbs as it will go to ground through the filaments head lamps /stop lamps ect.
That also applies if you are testing a lamp circuit across the fuse method

For me I have never disconnected dash bulbs as they draw so little it will not ground the test bulb but I think they may read on your ohms meter.

Put the lamp across the pos term or fuse and other lead the pos battery cable or load side of the fuse .
If you have a short it will light up because it has power on one side and earth on the other.
Disconnect components until the light goes out, thats your short, if wiring has chaffed and grounding you need to move the lome till it goes out and that will give you somewhere to look.
If you have a main plugs half way down the car disconnect it, if the light stays on its in the front half not the back.
If it goes out its in the rear from that point on

If you have a short to voltage it works the same way,use a volt meter or lamp.
As you have v on a ground wire if you put a meter across ground wire and to bat neg it will read voltage, go through the disconnection processes to find it.

I think the 20 ohms will be dash lamps.
That why you use a headlamp bulb or 5watt bulb as the dash lamps will not be enough ground for it to light the bulb.

Jim
 
Last edited:

Mike

Lifetime Supporter
Thanks Jim. You all have been a great help in providing techniques for understanding my car better. Looking forward to looking over Blas' wiring schematic.
 
Back
Top