Blowing backup lights fuse when putting in reverse

[Whitefirstgen]

Ok so I have done some trouble shooting but could use some help.

I removed all non factory wiring (,trailer plugs etc).

Traced all wires under truck and found no shorts

Removed the bulbs

Then i disconnected the blue connector under the dash which I was told separated the fuses and internal wiring from the wiring under the truck. The fuse still BLEW!!

Any thoughts?

Mike

 

[Simplysmn]

You have a Bad switch on the trans your truck have a 518 ? if so the switch on side of trans is for back up light's and Netural safty start switch replace it and see what happen's . Or double check the fuse link's on the fender well and trace the wires going down to trans . we had a truck that was blowing the start circuit at turn of key and it turned out to be wires going to trans area shorted out . If you just undid the blue connector the trans wiring was still hooked up it goes from TPS,CPS and part of pump down to trans has nothing to do with blue connector .

 

[Whitefirstgen]

i do not know which transmission. I will have to try to look it up somehow. was told it was the original for the 92 W350 Auto. any how to videos on replacing this switch?

 

[Simplysmn]

Very Easy you will have to drain some fluid from the Trans Pan but the switch Unscrew's from side of Trans Very easy .Go to NAPA and tell them you need a Netural safty switch for a 93 dodge 518 auto trans once you get the new 1 you will see what I am talking about . shouldn't take more then 30 min's to change it out . Also when you check fluid make sure trans is in Netural .

 

[Whitefirstgen]

OK sounds like the 518 is the only auto trans for that year. i looked at some pictures of some of these switches. You are right does not look complicated. Surprised the switch fails in a manner that causes a dead short but i will go with that theory....

 

[Simplysmn]

Before you change the switch out double check the wiring followit up the trans and into the Motor you may have a wire shorted out but I am stillthinking the switch is bad .But it won't hurt to check everything before you change it out .

 

[Whitefirstgen]

Update - pulled connector off switch and was able to put in reverse without fuse blowing. Removed switch and installed new switch, connected back up and THE FUSE BLEW AGAIN! I tried to follow the wires up into the engine and could not see any issues but pretty tough. If there was a ground in the wires i would have thought the fuse would have blown when switch was disconnected. I tested the switch and it appears to work very similarly to the old switch. If it go across the outer posts with switch closed i do not get 0 ohms, the new switch is 0. Any thoughts?

 

[Whitefirstgen]

I also pulled the connector back off and spun it 180 deg thinking maybe the orientation was important. Put in reverse and the lights came on for 5 secs and fuse blew.... That is the longest the fuse held but what the heck????

 

[Simplysmn]

OK 2 thing's first disconnect the wires fromtrans and pull the harness up to top side of motor then trace every wire you either have 2 wires shorting out on that harness or 1 of the wires going to reverse light's is shorting to ground where about's are you ? maybe someone close by could lend a hand .

 

[Whitefirstgen]

And thoughts on maybe the connector is bad? I disconnected wires under truck so it has to be wires from under dash to the NSS. I been looking and all looked wrapped and no obvious. Guess I have to get more agressive with wires. BTW does the plug need to be oriented one way or another. I have a guy two hours away that should be able to help. But have not been lucky enough to get ahold of him lately.

 

[Simplysmn]

no the wires can go either way but I think you have a short in the wiring going up tward's Motor Or on frame going back to Taillight's 1 of the 2 double check all your wires .

 

[Whitefirstgen]

Nope. Ran to advance for late night parts grab. Got the 3 pin connector and pig tails. BAM lights work!! Connector had the short in it. Frustrating but soooo glad it wasn't wiring. Thanks for your help and quick replies!

 

[Simplysmn]

WOW kool glad you fixed it . I agree I hate wiring also but I'm getting better as I build truck's .

 

[Whitefirstgen]

Stinks - switch was fine and all the trailer wiring was good. All I would have had to do was replace that connector. But at least it works and i can get truck inspected!

 

[Whitefirstgen]

Unbelievable. Fuse and lights worked until I started truck and shifted to reverse. Then fuse blew! How is that possible??

 

[seafish]

Not really sure how that i spossible, but if the connector was in such poor shape, it is possible that there is still an intermittent short in the switch or perhaps you need to go back and check your work on splicing in the connector.

 

[Whitefirstgen]

I replaced switch first so that is also new. What changes when truck is running vs just switch on? I checked it 3 times lights stays for got 30 minutes not problem with switch on and truck in reverse. As soon as i start truck and put in reverse the fuse blows. The only diff is the oil in the transmission. But not sure how that could impact. I did notice oil level is still low after losing a bunch replacing switch, added two quarts but need to add at least one more. Could low oil impact switch in any way?

How about voltage being higher when truck is running?

Funny thing is it was blowing fuses without truck running before, now that works just fine...... Oy!

 

[Simplysmn]

Start looking into the Frame Harness I bet you will find your Problem .

 

[Whitefirstgen]

i disconnected the plug that takes away the frame wiring and still had ground. Has to be in wiring thru firewall. Doesn't look like fun.

 

[Simplysmn]

Easier then you think just take your time .but the trans harness is seperate from Frame harness thou .