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1G Need Help Finding a Short!

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90 TSI FWD

15+ Year Contributor
264
11
Oct 26, 2004
Columbus, Mississippi
Whenever I turn the ignition switch to ON, the ignition fuse on the positive battery terminal (30A) blows. I printed out this wiring diagram, and started to disconnect things that could be grounded, but the fuse kept blowing. I went through about 10 fuses I had laying around before I realized how stupid I was for wasting them.

Things I disconnected, yet still had the fuse blow:
Starter
Radiator fans
Alternator
Coil pack/other plug underneath it (forgot what it's called)
Radio
MPI/Other fuse on the positive battery terminal
Fuel pump

Other things I've checked:
Took the fuel pump out the check wiring
Changed pump rewire relay
Tested Starter
Cigarette lighter wiring

Then I got around to pulling the dash apart and borrowed a meter to test continuity. I placed one end on the prong for the ignition fuse at the positive battery terminal, and I placed the other on the ground. The system was definitely being grounded only when the key was turned ON. I left it on there while I kept disconnecting things to see if the resistance would go up (ground contact would decrease - good thing). When I unplugged the turbo timer, the ohm reading went up a little. I don't know what that meant, but still, the system was being grounded with it removed.

Here's the plug that goes to the ignition switch (Connector A). This is as if you unplugged it from the rest of the car and are looking at the prongs (I believe) that go to the switch:
(Taken from the Haynes manual)
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Colors:
1 - No wire
2 - Blue/Black stripe (LB)
3 - Blue (L)
4 - Black/White stripe (BW)
5 - Black/Yellow stripe (BY)
6 - White (W)

I did a check for continuity using the bottom image in the above picture to test the switch is working properly. It passed. I also checked what wires from the plug-to-harness were continued. 4-2 and 4-5 had continuity (thus 2-4-5).

Edit:
Also, with the meter connected again to the ignition fuse on the positive terminal and a ground, I disconnected the ignition switch plug to the harness.  I then used a wire to make connections on the plug-to-harness.  The meter found that the system was being grounded when 6-2 OR 6-4. You can see above that when the ignition is turned ON, 2 and 4 is added to the circuit.   Also, from the above paragraph, you can see that 4-2 has continuity, so this does make sense. BUT, is 4-5 supposed to have continuity?  This is telling me that when the key is ON, I'd have 6-3-4-2-5 instead of 6-3-4-2 as shown in the manual, correct?

The following wires were tested for continuity at a ground with the key turned ON. These listed are grounded at some point in their wiring.
Plug to switch
2
3
4
6

Plug to wiring harness
2 - highest ohm reading compared to the other two (weakest ground, but still present)
4
5

I don't know what to do now. Can someone with wiring knowledge tell me whether or not any of these tests should not have tested the way they did?

Today's update

Okay. So I've been studying the electrical diagrams all night, and pulled some plugs again today.

The ignition switch connects two wires in the ON position: 2 and 4 as seen in this diagram. I decided to follow 4 first. You could see that 4 (BW wire) connects to two main plugs: C-54 and C-59.

I unplugged C-54 at the junction block (J/B) to eliminate the possibility of a short from there. The J/B is where all this misc fuses go near the driver's side kick panel. I turned the key to ON, and saw that I was still getting a short.

Next, I unplugged C-59. You can see what C-59 is from the following photos taken from projectzerog.com (source). C-59 is the blue plug in the second photo.

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Colors:
1 - White
2 - Black/Red
3 - Blue/Red (thinner wire)
4 - Yellow (thinner wire
5 - Black/White (thicker wire)
6 - Black/White (thinner wire)

After unplugging C-59, I no longer had a short. My problem lies within the circuit of this plug. I checked to see which wires of the plug experienced a ground. On the male side (plug to ignition), 4, 5, and 6 were grounded on ACC. 1, 4, 5, and 6 grounded on ON.

On the female side (plug to harness in first picture), 2, 3, and 5 were grounded. Now I need help to determine whether or not the aforementioned is supposed to be this way or not.

For those willing to help who have a FSM, please let me know what wires to check, or what I should do next. I could email you a copy of the manual if you'd like. It's about 15 MB. Thanks!!!!
 
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Alrighty. I focused on C-59 for a while, and here's what I found out.

Connecting the number 1 (White) wire on C-59 creates the short. The other 5 don't when they are connected. BUT, here's the thing. It only shorts on ON. 1 on the male side is only active when it is on ON. Also, 1 and 5 on the male side are connected on ON. Does this mean my short is on the male side, number 5 (BW) wire?

This seems possible, BUT 5 and 6 already experience a ground on ACC. Why wouldn't something blow then?

I need to find out where 1 (W) on the male side goes to. It's nowhere to be found in the FSM. Since 1 is connected to 5 when on ON, I'm thinking it's on the BW wire. There's just LOTS of wire loom to unravel, and to get to. What if I just buy a long wire, and wire it from the ignition plug to C-54 and C-59. If the short is in this wire, that should fix my problem, right?

Followup post:

I've just about had it with the car. There's no consistency in the harness, and it pisses me off. There's a short when:

- C-59 plugged, C-54 unplugged, coil pack/transistor plugged
- C-59 plugged, C-54 plugged, coil pack/transistor unplugged

Note: Coil pack and transistor both have to be plugged for a short. Not one or the other.

There is no short when C-59 is plugged, and the other two are not. Well, there's a TINY reading, but not as much as the other scenarios.

I connected the plug at C-59 by means of wires and prongs. I disconnected them to make different combinations. Only 1(W) and 5(BW) are involved with my problem. I did find out 1(W) goes from the ignition fuse to the plug, then from the plug to the ignition switch. When the key is ON, 1 connects to 5. 5 is being shorted, thus my problem.

From the plug that goes to the harness (shown in the first picture of post #6), 5 is grounded when both the coil pack and transistor are plugged in.

From the plug to the ignition switch, 5 is grounded with C-54 is plugged in.

After I discovered the above, I went crazy, and said F it. I'm just about at that point to where I've given up. I've wasted my whole break on this stupid electrical problem.
 
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First be sure to trace the appropriate circuit depending on the ignition key position. next is I say Bro that schematic you got pretty much leaves out allot. If your blowing Fuse #3 an 30Amp fuse (Pink) in color main fuse on battery terminal, that goes straight into the ignition switch first and outputs on 4 different wires, which is why you have been blowing all those fuses.

There is a dead short internally inside that switch I would bet, especially you have disconnected and isolated a majority of the connections beyond the Ignition switch itself. I have 2 different test lights that can check for various shorts to ground, short to power and continuity test the circuit to check for breaks or opens. If your still having problems send me a message. I have both 1990 and 1992 Laser/Talon Factory service manual for Electrical schematics that are often left out in publications such as Haynes and Chilton Manuals. I'm about an hours drive North of you so let me know in advance when you can if your still havin problems. I need to hit a few boneyards down that way anyways so I can swing by when I get done looking for a front bumper, if need be.
 
Stars, I tested the switch for shorts already. I am using the FSM. I'm mainly jumping from the 30's, 50's, 70's, and 180's (page numbers) in the electrical manual.

I was able to discover why I got a short from plugging the coil pack and transistor. My transistor (and my two spares) failed this test. There was continuity between 1 and 3 prior to the 1.5V being hooked up. Following the diagram, this meant that the BW wire, through connection of the coil pack, touched ground through connection of the transistor. I'm hoping I could find a local with a spare.

I still need to discover why it shorts when C-54 is plugged in. It goes to the junction box (J/B), but I would think that one of those fuses would have blown before the ignition if there was a short there. I'm going to look through the diagrams again, and maybe test the wires at the box individually. It just sucks as it is very difficult to access.
 
"It goes to the junction box (J/B), but I would think that one of those fuses would have blown before the ignition if there was a short there."

Yes, you are correct. let's say that within that J/B you cannot see inside; is that of the problem that is suspected to be maybe an internal short inside that J/B? Somehow, let me say I should be doing psychic readings instead of working on cars...LOL.. that she got hot and melted causing a short to ground on the inside? I have seen that one stump many good electrical techs. You've done a good job at back tracing the circuit and know which color wire your after.

I usually get out the razor blade and start cutting the wire loom open on every bundle of wire going to a J/B or P.D.S. This is depending on your electrical taping skills if you want to go this route. If the wire bundles check out good, no melted wires or connectors then your almost certain it is within the J/B itself that is the cause of the blown fuse at this point because you have ruled all other sources out of the equation. It is a process called elimination and sooner or later you get back to the cause or source of the problem. Either way yes, it is time consuming that is why the shop where I work at charges $80.00 an hour to find this kind of problem; so best to know what your doing and look at the money you have already saved by putting in the hours and doing the work yourself. ACE Pick a Part and Jax U Pull it may still have some DSM's left to boneout for your local parts needs, you'll have to go check them out they will not tell you what vehicles they have in the yard.
 
Hi 90 TSI FWD

We just picked up a 90 Laser Turbo with an electrical issue like yours from when you posted about way back when. I really like your write up and explanation.

The ignition fuse keeps blowing when the key is turned to ON. Also there is no power to the dash or any accessories in the ACC position. The only thing that is on is the light for "door ajar" and the two lights in the floor board by the driver and passenger doors.

We traced it down to that same connectors you mention in your posts and the black with white stripe wire. I put the multimeter and noticed it was going to ground but wasn't 100% sure if it is suppose to be ground or it means a short. The next step for us to check is the thing with the coil pack that you mentioned is your last post.

We have been racking our brains and tearing up the interior trying to find the short. We even replaced the ignition switch for the key thinking that was the problem. I appreciate your time and hope to hear back on your solution. Thank you!

P.S. Sorry for bringing back such an old post. We are too new to private message members. Your help is greatly appreciated.
 
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