Tail Lights/Parking Lights/Interior Dash Lights blow the fuse

smetzger

03 P5 (x2), 09 Miata, 07 Mazda3, 13 Fit, 09 Ody
As soon as I turn the stalk to parking light the Tail Light Fuse will blow.
This Fuse is also linked to interior lights.

Things I have tried...
1) Replacing the fuse
2) Using a higher rated fuse (30a as opposed to the 15a) also blew immediately
3) Pulled the interior light dimmer switch, fuse still blows when this is disconnected.
4) Fortunately (or unfortunately, depending on how you look at it) I have another Protege. I took the TNS from the problem car and put it in the good car and everything still worked. So, it is not the TNS relay.

Any ideas?
 
I would pull the tail lights and check the harness for a short to ground, possible the harness was pinched or installed incorrectly and it has rubbed through the insulation.
 
I'll check the taillight harnesses.

I guess I am going to pull/disconnect one by one everything that is connected to that fuse, if I disconnect something and then fuse does not blow then that is what is causing the short.
So, what is on this fuse??
Tail lights
license plate light
instrument cluster illumination (not looking forward to pulling the dash apart)

Anything else?
 
This might help a bit...
(sections E5 & E6 aren't shown in the wiring diagrams.)

Looks like they should all be light blue wires with a black stripe.

 
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I pulled all the tail light bulbs (unfortunately there is no plug into the wires to pull) and pulled the whole license plate light assembly (both).
Fuse still blows.

Is there some better way I should be testing this?

Also, just to make sure. Is this the TNS relay?
IMG_0660.jpg
 
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This might help a bit...
(sections E5 & E6 aren't shown in the wiring diagrams.)

Looks like they should all be light blue wires with a black stripe.


Correction... LG/B is a light green wire with a black stripe.
 
I found a bunch of diagrams that should help.

Their is apparently connectors for the rear light assemblies...

If you disconnect a bunch of connectors, you maybe able to isolate the bad stretch of wire.

It may be shorted in a socket as well so a disconnection would isolate it.






















 
Also, just to make sure. Is this the TNS relay?

I'm thinking your TNS relay if fine because it is switching and feeding power to the tail fuse.

If the TNS relay itself were shorting to ground it would probably blow the 100 amp main fuse.
 
You can disconnect any connector with a LG/B wire in it and test both sides of the connector at that wire.

With your ignition off and your taillights off (maybe even disconnect the battery like you're supposed to), set your multimeter to Ohms and put one probe on the wire and the other probe to chassis ground. You should get OL or infinite resistance.

If you probe the side of the connector that goes to a bulb you will get the resistance of the bulb which will be low but NOT zero ohms.

If you disconnect the junction between the front and dash harness. you can isolate the circuits.

Their is probably a point where one LG/B wire goes into a connector but two or more come out the other side (of the same pin)... That's where it would split to to go the left and right sides.
Try to separate the wires (maybe even cut them) and test them individually.
 
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I pulled all the tail light bulbs (unfortunately there is no plug into the wires to pull) and pulled the whole license plate light assembly (both).
Fuse still blows.

You can test for ohms right in the bulb socket. Test for ohms (power off) between the positive and ground of the socket.
You will probably get zero ohms but unfortunately you will have no idea where the short is... It could be in the socket or wires for the front side marker lights ??

That's why you need to separate the circuit wherever you can to help isolate the problem.
 
1) I tested the TNS Relay (the correct one this time) and it is ok
2) Disconnected the instrument cluster and the fuse still blew
3) Disconnected both side marker lights and the parking light inside the headlight, fuse still blew

I tested for continuity to ground on the cluster and I was able to get it.... but I then tested other wires and they also tested positive for continuity to ground. So, I don't think that test is valid.

I can't get to those connectors in the taillights, or at least can't figure out how to.

You said "If you disconnect the junction between the front and dash harness. you can isolate the circuits."
Where is this junction, how do I do this?

Thanks,
Scott
 
The junction is at connector X 01 ...

It looks like it's up under the dash to left.

Try to disconnect it and see of the fuse still blows.

I figure the power goes through the TNS relay then the fuse then goes to that connector. Try to isolate as much of the wires of the circuit as possible.

Try to remove all your lightbulbs on that fuse so your not measuring their very low resistance. Check the sockets while you're at it to check for damage or shorts.




 
I found it...

This is where all the LG/B wires come together.

Connector X-18




 
I'm guessing that's where a single power wire from the tail fuse gets split and goes to left and right side marker lights and L&R taillights.

Disconnect it and leave all your bulbs and housings in place.
Then try your lights again.
I'm guessing you will no longer blow a fuse.

If no fuse blows, then feed +12 V (or a jumper wire from the positive feed in the connector) to each of the four terminals one at a time to see which one blows the fuse.

Take note of what lights light up to find out what corner of the harness is bad.

Then cut the wire from the bad circuit about three inches back and splice in a new wire to run to the proper corner and splice back in.
 
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You can also use your voltmeter to test the X-18 connector by disconnecting it and turn on your taillights. If your fuse doesn't blow, then test for voltage in the connector terminals.

You should get 12 V on all four.

Then use your ohmmeter to test the four terminals on the other side of the connector.

One of them is probably shorted.

You can then cut that wire, reconnect the connector and verify that the other three corners are lite up.
 
ok, I got frustrated and took it to my shop.

Turns out there was a loose wire that connected to the radio-head unit. I assume it was the wire that dims the head-unit when the lights are on. So, that's yet another one on this circuit. aargh $360. But at least it is fixed and wasn't something truly major.
 
Engineer's have wire routing down to a science.. If there's an electrical problem, you can almost always trace it back to something that somebody has dicked with in the past..
 
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