Wiring Issues... (1 Viewer)

thecrazygreek

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Just getting my 76 resto wrapped up. And I am just STARTING to hook up all the lights.

Still dont have the rear running side lights hooked up but everything else is connected.

OK, I turn on the lights, and get headlights but no taillights, or running lights.

I hit the brakes, and I get Brake lights!!! but the front PS signal turns on as well. wtf???

Also, when the lights are on I am not getting power at the proper places. ie the running lights arent getting voltage.

Can I at least test for power without everything hooked up? I dont need to install all lights just to check it right?

Example: I want to see if I am getting 12v at the wire that goes to the PS rear running light, I touch meter to wire, and ground lead to good ground. I'm not getting anything, I dont need ALL lights grounded just to test do I ?

I will be jumping back into this later today and just wanted to run this by someone to get my thinking cap straight.

This is all on a freshly cleaned, re-wrapped wire harness.

Fuses are all good...

:bang:
 

Coolerman

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I test all my harnesses on the bench with NO lights connected to verify the wiring using just a volt meter, THEN connect ALL lights with jumpers for grounds to verify full functionality.

Turn/hazard wiring testing will require all lights be connected and grounded. Your going to have to do it anyway... :D

A +12V buzzer is a good trouble shooting tool. Make some adapters so you can plug it into various connectors on the harness, ensure it's grounded then you can test without having to SEE what you are doing.
 
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I agree you have a ground issue, when nothing makes sence always check your grounds. If you are grounding over a newly painted area grind to bare metal and ground. I like to use grounding washers availible at any hardware bolt rack, they have teeth that bite through paint and corrosion. The paint over the connection to keep it from rusting. Ground the engine block to the battery and the body and the block to the chassis. I add grounds in the back as well for the truck and if you tow anything. I am bald now becuase of grounds well at least that is what i am blaming it on. Good Luck.
 
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Ditto on the grounds.

If a light doesn't work, it could be the power or it could be the ground.

Here's how I would approach it. Get or make a jumper cable long enough to reach from the battery to every light on the car. Connect it to the neg terminal on the battery. Bring it around with you when you test each light. This takes the ground out of the question To see if you've got power, connect the meter between the wire to the light and this ground jumper cable. If you've got power and the light doesn't work then it's the ground. To fix the ground, clean up the metal to metal connections by removing any rust or paint, tighten screws, replace rusty screws, etc.
 

thecrazygreek

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OK, heres what Ive done.

Checked running lights in the front, no go... BUT when I unplug the rear harness, I get about 9 volts to the front running lights. Does this mean that when its all connected the rears are not grounded well enough which causes the whole running light system to fail?

This is real time btw...

:beer:
 
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Checked running lights in the front, no go... BUT when I unplug the rear harness, I get about 9 volts to the front running lights. Does this mean that when its all connected the rears are not grounded well enough which causes the whole running light system to fail?
It means you have a short to ground at the rear. For your test ground, hook up a jumper cable directly to the battery. Getting the test ground right may be part of the problem you're having diagnosing the real problem.

Clean your main battery-to-frame negative contact and make sure it's tight.
 

Rockets2000

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Partial voltage could also be a dirty/corroded connection. I know you said you have good fuses, but did you clean the fuse holders on the fuse block?
 
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I hit the brakes, and I get Brake lights!!! but the front PS signal turns on as well. wtf???

:bang:
Most likely an indication that the rear PS lamp housing isn't grounded properly, feeding back power into the turn signal bulb, which finds a ground at the front.

Checked running lights in the front, no go... BUT when I unplug the rear harness, I get about 9 volts to the front running lights. Does this mean that when its all connected the rears are not grounded well enough which causes the whole running light system to fail?
The lack of running lights may be a bad light switch.

Partial voltage could also be a dirty/corroded connection. I know you said you have good fuses, but did you clean the fuse holders on the fuse block?
x3 Chances are that the voltage drop is due to the resistance of a bad connection. If you measure voltages on an open circuit (like without a bulb), you can get fooled as you will see full battery voltage even with a bad connection because of the sensitivity of the volt meter. The meter resistance is too high to load the circuit and see the voltage drop. I prefer to have the switch turned on and leave everything plugged in and measure the voltage starting at the bulb and working back in the circuit until the voltage jumps up to 12V. When the V jumps up, you have a bad connection somewhere between that point and the previous one.
 
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triple ditto on grounds. I work on german cars for a living, electrical nightmares, always ground or backfeeding because of grounds.. volt meters only tell half the tale. you may have high resistence in some places causing a backfeed
 
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You say "no go". What exactly does that mean? The light doesn't light? No voltage?

You say that you measure 9v at the light. 9v between the light and what?
Did you run a solid test ground from the battery as we suggested?

9v could come from a discharged battery, a resistive fuse connection, or a resistive ground. The answers to these questions will help decide which it is.
 

thecrazygreek

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You say "no go". What exactly does that mean? The light doesn't light? No voltage?
No voltage

You say that you measure 9v at the light. 9v between the light and what?
Did you run a solid test ground from the battery as we suggested?
Yes 9v with one end on the green wire to the PS running light and the other to the batt negative.

9v could come from a discharged battery, a resistive fuse connection, or a resistive ground. The answers to these questions will help decide which it is.
Batt is at 12.5 volts when not running. Alt is working at 14.5ish when charging. The fuseblock is super clean and soda blasted... Dumb question, but does the fuseblack need a great ground at the block? Its bolted in but with fresh paint, I may need to do some tapping...

OK so here is another question... Please tell me what year harness I am using. I cant find this color scheme anywhere. I purchased it from another mudder as a 76-77 but the colors dont jive. The wire colors at the rear going into the tail lights (each side) are as follows... Two green (running) One Black (figured this to be stop lights) One Blue (figured this to be Back up Light) and one white (figured this to be turn signal / hazzard) There are NO stripes on these wires...




Does anyone have the same? If so what year is it? Coolerman??? Maybe you have seen this one?

Anyone?

Thanks for the answers btw. Great help, just need to resolve this issue. I think however, that the real issue is two wires are touching each other in the sheathing and cousing that "short to ground" someone mentioned earlier...

ANd Have also just pulled the rear harness and performed a continuity check and everything seems to be ok, but as you know, wire can shift around and be good one minute, and bad the next... :bang:
 
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It is not stock wiring in the picture. There are very few ground wires, let alone ones that run in the harness with other wires, so the chances of a short to ground are slim.
 

thecrazygreek

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It is not stock wiring in the picture. There are very few ground wires, let alone ones that run in the harness with other wires, so the chances of a short to ground are slim.
Oh yes, this is stock wiring... I kid you not...

Here is the other end...

Notice the solid green, black and white wires, no blue because it starts at the Back up light and goes back... these wires are still in some of the original inner wrap from the factory...

Also notice the "normal" wires, ie yellow and red for fuel sender etc etc... why me...? :mad:

 
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I have never seen those color codes used for tail light wires on any Toyota and they don't agree with any schematic I have. Maybe somebody replaced them with generic wires? If so, at least the plug may work properly.

There aren't any ground wires for the rear lights. That is why they have so many problems with bad grounds.
 

thecrazygreek

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Again, these are still (partially) in the factory wrap, from Toyota... When I started cleaning it up it even had an original sticker on it. I am going to re-install tomorrow and make sure I go through each wire one by one... I have re-tapped all the holes I am going to use for grounds, and also cleaned / retapped the neg batt cable mounting location.
 

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