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Stuck in Flagstaff - Back up light wires blowing GUAGE fuse

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Stuck in Flagstaff - Back up light wires blowing GUAGE fuse

Old 05-21-2019, 10:38 PM
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Stuck in Flagstaff - Back up light wires blowing GUAGE fuse

Aloha YT,
Stuck in Flagstaff trying to figure this out. I am on my way to school out east and need to be on the road asap. I bought a used 93 4runner yesterday (3VZE, 5sp, 4WD) and when I got off the road in Flagstaff today I noticed my gas guage was not moving after filling up: nor were the tach/speedometer/ac/heat/windows working. I checked and the GUAGE fuse was blown. Replaced the 10A GUAGE fuse and as soon as I shifted into reverse, POP. I researched the issue and it appears to be the back up light circuit grounding somewhere (I went through a few more fuses to make sure, as soon as the stick shifts to reverse POP). I removed the backup light housings and checked the wires. While old, they seem to be solid and notshorting anywhere. I got under the truck and checked the wires by the transmission (still not clear on what is what down there as I cant find images of the connector referenced in the FSM) and no wires seem to be nicked/pulled from the connector seating/grounding anywhere. I am in a jam and would appreciate any help guys. Mahalo in advance gentlemen. It's sleeting out now, I will post pics first thing in the morning.

-R

Last edited by surf4life; 05-22-2019 at 10:05 AM. Reason: Update trans
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Old 05-22-2019, 05:45 AM
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Originally Posted by surf4life View Post
Aloha YT,
Stuck in Flagstaff trying to figure this out. I am on my way to school out east and need to be on the road asap. I bought a used 93 4runner yesterday (3VZE - 4WD) and when I got off the road in Flagstaff today I noticed my gas guage was not moving after filling up: nor were the tach/speedometer/ac/heat/windows working. I checked and the GUAGE fuse was blown. Replaced the 10A GUAGE fuse and as soon as I shifted into reverse, POP. I researched the issue and it appears to be the back up light circuit grounding somewhere (I went through a few more fuses to make sure, as soon as the stick shifts to reverse POP). I removed the backup light housings and checked the wires. While old, they seem to be solid and notshorting anywhere. I got under the truck and checked the wires by the transmission (still not clear on what is what down there as I cant find images of the connector referenced in the FSM) and no wires seem to be nicked/pulled from the connector seating/grounding anywhere. I am in a jam and would appreciate any help guys. Mahalo in advance gentlemen. It's sleeting out now, I will post pics first thing in the morning.

-R

This light is triggered by a sensor on the trans. You didn't mention whether or not it's a 5sp but I would start at the sensor on the transmission and work my way back looking for shorts, could also pull the plug on it and not use backup lights for now so you can keep all the others.

On the R150F 5 speed trans in my 1993 it's on the passenger side of the transmission.
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Old 05-22-2019, 08:40 AM
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Originally Posted by COMTB View Post
This light is triggered by a sensor on the trans. You didn't mention whether or not it's a 5sp but I would start at the sensor on the transmission and work my way back looking for shorts, could also pull the plug on it and not use backup lights for now so you can keep all the others.

On the R150F 5 speed trans in my 1993 it's on the passenger side of the transmission.
Yes it is a 5 speed. I see a connector on the passenger side. I will post a pic in a minute.
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Old 05-22-2019, 09:37 AM
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Personally, I'd first pull the taillights assemblies, disconnect both (R5 and R6, 6-pin connectors), then risk a fuse. Then plug them back in one at a time. It seems more likely to me that the short to ground would be back in the housings (lots of wire exposed to the elements) than in the reverse switch itself. More importantly, these tests would be easier to do. If disconnecting the taillight assemblies doesn't stop the fuse from blowing, then the short is somewhere between the reverse switch and the taillight assembly.

Last edited by scope103; 05-22-2019 at 09:40 AM.
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Old 05-22-2019, 09:54 AM
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Originally Posted by scope103 View Post
Personally, I'd first pull the taillights assemblies, disconnect both (R5 and R6, 6-pin connectors), then risk a fuse. Then plug them back in one at a time. It seems more likely to me that the short to ground would be back in the housings (lots of wire exposed to the elements) than in the reverse switch itself. More importantly, these tests would be easier to do. If disconnecting the taillight assemblies doesn't stop the fuse from blowing, then the short is somewhere between the reverse switch and the taillight assembly.
Do you mean the backup light assemblies? That is an easy enough test.
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Old 05-22-2019, 11:02 AM
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Originally Posted by COMTB View Post
This light is triggered by a sensor on the trans. You didn't mention whether or not it's a 5sp but I would start at the sensor on the transmission and work my way back looking for shorts, could also pull the plug on it and not use backup lights for now so you can keep all the others.

On the R150F 5 speed trans in my 1993 it's on the passenger side of the transmission.
I see two sensors on the passenger side of trans, which is it?

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Old 05-22-2019, 11:24 AM
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I checked the drivers side back up lights with a voltmeter with all 4 bulbs removed, The smaller bulb terminals are shorted (green & white/black wires) yet the larger bulbs are not (red yellow & white black)




Last edited by surf4life; 05-22-2019 at 11:32 AM.
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Old 05-22-2019, 12:15 PM
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Update

Disconnected the backup light sensor and problem solved, it was covered in oil and pretty shot


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Old 05-22-2019, 03:09 PM
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You've prevented the backup switch from connecting to the short, which should be enough to get you out of Flagstaff.

But you still haven't found the short. According to my EWD, the G and W-B wires are to the tail lights Since they are all connected in parallel, checking the resistance on one (or two) sockets will just measure the resistance of the remaining bulbs. 14.1 ohms sounds like the right number. The stop lights are G-W to W-B, and the turn signals are G-B and G-Y to W-B. Last, the Backup Lights (the ones you're interested in), show as R-B to W-B.

I'll bet the R-W wire on your now-disconnected backup switch is shorted to ground. Assuming your backup bulbs are connected to R-Y, and your test indicates that's not shorted to ground, I'll bet it's disconnected from the backup switch, and where that disconnect takes place, the wire from the backup switch is shorted to ground.

The oil on the switch is not a good thing, but I doubt the switch or the oil is your problem. You can test the resistance to ground on both switch terminals (should be infinite). The B-O wire in the connector will have battery voltage with key-on, and the R-W, which SHOULD go to the lamps in back, will show a short to ground.

Last edited by scope103; 05-22-2019 at 03:11 PM.
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Old 05-22-2019, 08:22 PM
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Originally Posted by scope103 View Post
You've prevented the backup switch from connecting to the short, which should be enough to get you out of Flagstaff.

But you still haven't found the short. According to my EWD, the G and W-B wires are to the tail lights Since they are all connected in parallel, checking the resistance on one (or two) sockets will just measure the resistance of the remaining bulbs. 14.1 ohms sounds like the right number. The stop lights are G-W to W-B, and the turn signals are G-B and G-Y to W-B. Last, the Backup Lights (the ones you're interested in), show as R-B to W-B.

I'll bet the R-W wire on your now-disconnected backup switch is shorted to ground. Assuming your backup bulbs are connected to R-Y, and your test indicates that's not shorted to ground, I'll bet it's disconnected from the backup switch, and where that disconnect takes place, the wire from the backup switch is shorted to ground.

The oil on the switch is not a good thing, but I doubt the switch or the oil is your problem. You can test the resistance to ground on both switch terminals (should be infinite). The B-O wire in the connector will have battery voltage with key-on, and the R-W, which SHOULD go to the lamps in back, will show a short to ground.
In Albuqurque now, before i left i probed the two sockets on the wire coming out of the backup light switch and they were shorted, with engine off and in first
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Old 05-23-2019, 05:29 AM
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Nice glad that quick fix worked.

You can try replacing the factory switch (mine was shot) or cleaning it up but it sounds like you're going to be tracing some wires to find your short (unless the plug itself for the bulb is shot but that's easy enough to see).

Goodluck and glad you're moving again!

Some wiring help:




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Old 05-23-2019, 11:32 AM
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The reverse lights switch commonly short out internally. They usually will either short to ground or stick the lights on all the time. Unplug the switch, and jump the connector with a paper clip. If the fuse blows, its an issue further down the line. If the lights work, put a new switch in it.
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Old 05-24-2019, 01:35 PM
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It looks like the back up switch is leaking internally causing the short. Replace the switch and check the trans fluid level, I think it's a 24 mm for the fill plug on the drivers side opposite of the back up switch. This same thing happened to me when I was traveling to Hawaii last month. I replaced the swich, fixed the leak and the short.

Last edited by ZTEC; 05-24-2019 at 01:38 PM.
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Old 05-24-2019, 06:39 PM
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Originally Posted by ZTEC View Post
It looks like the back up switch is leaking internally causing the short. Replace the switch and check the trans fluid level, I think it's a 24 mm for the fill plug on the drivers side opposite of the back up switch. This same thing happened to me when I was traveling to Hawaii last month. I replaced the swich, fixed the leak and the short.
Ok going to replace switch tomorrow. I drained the transmission today and refilled, it took about 6.5 quarts!!! Now i am overheating on inclines, starting a new threadon that now. 🤦˟♂️
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