Reverse Lights Short?
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From: Conshohocken, PA
Car: 1985 Pontiac trans-Am
Engine: 305
Transmission: T5
Axle/Gears: 3.27 9 bolt
Reverse Lights Short?
It's an 85 Trans-am with a t5. I was wondering if anyone knew the path that they routed the wires for the Reverse lights. I know it shares a fuse with the turn signals, and that the sensor is on the trans. Who ever had the car in the past decided to do some band aid repairs, and used a resetting circuit beaker for the turn signal fuse instead of repairing the circuit. It's fine with the turn signals on, but the second I put it in reverse you can here it pop, and the lights all dim. He also has the headlight motors working on a toggle switch he wired up instead of figuring out why the lights didn't come up with the switch(my best guess at the moment is Isolation relay? but I'm not 100% where that is located either. Is it the one near the battery?). I do have a Haynes manual, the diagrams don't show the reverse light circuit, nor locations.
Joined: Aug 1999
Posts: 19,282
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From: Lawrence, KS
Car: Met. Silver 85 IROC/Sold
Engine: 350 HO Deluxe (350ci/330hp)
Transmission: T-5 (Non-WC)
Axle/Gears: Limited Slip 3.23's
Re: Reverse Lights Short?
Welcome to TGO. Maybe some wiring help in the following link:
http://www.austinthirdgen.org/index.php?pid=19
JamesC
http://www.austinthirdgen.org/index.php?pid=19
JamesC
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Joined: May 2016
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From: Conshohocken, PA
Car: 1985 Pontiac trans-Am
Engine: 305
Transmission: T5
Axle/Gears: 3.27 9 bolt
Re: Reverse Lights Short?
Thank James. I had come across those diagrams the other day, I'm just not sure where exactly the wires run, & don't want to pull anything apart with out knowing I'm in a relevant area.
Last edited by Sanitarium; May 22, 2016 at 05:25 PM.
Thread Starter
Junior Member
Joined: May 2016
Posts: 17
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From: Conshohocken, PA
Car: 1985 Pontiac trans-Am
Engine: 305
Transmission: T5
Axle/Gears: 3.27 9 bolt
Joined: Nov 2002
Posts: 6,642
Likes: 403
From: Oyth
Car: 89RS vert
Engine: Erod
Transmission: 4L65e
Axle/Gears: BW, 3.27
Re: Reverse Lights Short?
Don't think they pass thru the firewall.Circuit starts at the shifter, when its in reverse.
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Joined: May 2016
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From: Conshohocken, PA
Car: 1985 Pontiac trans-Am
Engine: 305
Transmission: T5
Axle/Gears: 3.27 9 bolt
Re: Reverse Lights Short?
On the manual trans it goes to a sensor on the side of the transmission. According to diagram it's dark blue from fuse to sensor, light green from sensor to reverse lights. But there's multiple blue and green wires I see in the engine compartment? And I can't get under it right now.
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Car: Yes
Engine: Usually
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Re: Reverse Lights Short?
There's no "sen-sore" [/mrspock] for the backup lights; just a switch. 
Real simple.
Never heard of "isolation relay" for those either.
Use some logic:
Most likely thing to be damaged that would cause a short, is the bulbs and sockets. Does taking the bulbs out fix it? What do the sockets look like down inside?
ALL of the wires to the rear of the car are in the "Fisher Body" harness, including the backup lights. That connector is on the left kick panel, up high, near/above the hood release cable assy.
But, start at the bulbs. Go take a look there, and tell us whether you found the problem.
Real simple.Never heard of "isolation relay" for those either.
Use some logic:
Most likely thing to be damaged that would cause a short, is the bulbs and sockets. Does taking the bulbs out fix it? What do the sockets look like down inside?
ALL of the wires to the rear of the car are in the "Fisher Body" harness, including the backup lights. That connector is on the left kick panel, up high, near/above the hood release cable assy.
But, start at the bulbs. Go take a look there, and tell us whether you found the problem.
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Joined: May 2016
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From: Conshohocken, PA
Car: 1985 Pontiac trans-Am
Engine: 305
Transmission: T5
Axle/Gears: 3.27 9 bolt
Re: Reverse Lights Short?
When I had the tail light assembly apart nothing looked worn or corroded. The bulbs are good. I'm waiting on hatch shocks to come in to pull apart the interior back there. On automatics the shifter is where the reverse & neutral safety switch are located. On a T5 trans the reverse switch/sensor is the t5 housing, the wires do not seem to come through the trans tunnel, so I assume it is coming through the firewall. 82-86 firebirds don't have a headlight module and use a relay instead, the wiring diagram calls this an isolation relay(fiero use the same one). But I do not know where it is located, there's many relays in the area I'm not sure which is which.
Joined: Sep 2005
Posts: 27,871
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Car: Yes
Engine: Usually
Transmission: Sometimes
Axle/Gears: Behind me somewhere
Re: Reverse Lights Short?
Headlight relay is not related to backup lights.
Did the problem go away when you took out the bulbs and put it in reverse?
Did the problem go away when you took out the bulbs and put it in reverse?
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Joined: May 2016
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From: Conshohocken, PA
Car: 1985 Pontiac trans-Am
Engine: 305
Transmission: T5
Axle/Gears: 3.27 9 bolt
Re: Reverse Lights Short?
No, & headlight isolation relay was just a second question. This evidently was an on going problem before I bought it. I know there's a short to ground, I just have to find where. Who ever originally looked at it put a Resetting circuit breaker in place of the 20amp fuse to keep the turn signals working. When I put the shifter in reverse everything will momentarily dim and the circuit breaker pops. From this I can determine the dark blue wire is fine, due to it always being hot. I know the light green wire goes from the trans to inside the car(not sure where it enters) then travels to the back of the car for the two lights. I've been trying to figure out what part of the engine harnesses the wires run through so I can try to chase it. But they're are multiple light green & dark blue wires in different circuits.
Joined: Nov 2002
Posts: 6,642
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From: Oyth
Car: 89RS vert
Engine: Erod
Transmission: 4L65e
Axle/Gears: BW, 3.27
Re: Reverse Lights Short?
Grn/bl are one circuit, "hot in run".The back-up switch just disconnects them when not in reverse.Blue from fuse to switch, grn from switch to sockets.The turn flasher is also on the blue (wire) portion.
Which wire is the c/b on?
Which wire is the c/b on?
Joined: Sep 2005
Posts: 27,871
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Car: Yes
Engine: Usually
Transmission: Sometimes
Axle/Gears: Behind me somewhere
Re: Reverse Lights Short?
Sorry, missed the part about the headlights in the initial post. Can't help you there, no telling what some hackjob moron did to your wiring. Some people should simply not be allowed to own dykes.
Green wire from the switch is the one that's hot only when in reverse. Goes from the transmission to the main bulkhead connector under the fusebox; then to the Fisher Body connector which if memory serves is above the hood release assy; then from there to the rear of the car. Might be another connector somewhere along the way. Find the Fisher Body connector first though, and unplug it, and see if it still does it. That'll at least cut the whole circuit roughly in half.
Green wire from the switch is the one that's hot only when in reverse. Goes from the transmission to the main bulkhead connector under the fusebox; then to the Fisher Body connector which if memory serves is above the hood release assy; then from there to the rear of the car. Might be another connector somewhere along the way. Find the Fisher Body connector first though, and unplug it, and see if it still does it. That'll at least cut the whole circuit roughly in half.
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Joined: May 2016
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From: Conshohocken, PA
Car: 1985 Pontiac trans-Am
Engine: 305
Transmission: T5
Axle/Gears: 3.27 9 bolt
Re: Reverse Lights Short?
Alright thank you. And yeah some people should be kept away from working on their own cars. It's amazing the way it was fixed shows some knowledge of how it works, while being more complicated then actually fixing the problem the right way.
Thread Starter
Junior Member
Joined: May 2016
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From: Conshohocken, PA
Car: 1985 Pontiac trans-Am
Engine: 305
Transmission: T5
Axle/Gears: 3.27 9 bolt
Re: Reverse Lights Short?
Turns out the backup light switch was shorting out into the T5 housing.
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Joined: Apr 2015
Posts: 15
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From: Phoenix, AZ
Car: 1987 Firebird Formula
Engine: 305 TPI
Transmission: T-5
Re: Reverse Lights Short?
Hey Sanitarium, I've got the same problem going on here. My '87 came from the factory with an auto trans but some PO swapped in the T5 and didn't bother installing a backup switch. So I put one in a few months ago and it worked perfectly for a while, but now it's blowing fuses. I re-checked all of my work and it's intact. So how did you determine the switch was shorting to the trans housing?
Thanks
Thanks
Thread Starter
Junior Member
Joined: May 2016
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From: Conshohocken, PA
Car: 1985 Pontiac trans-Am
Engine: 305
Transmission: T5
Axle/Gears: 3.27 9 bolt
Re: Reverse Lights Short?
Honestly I used a pover probe short finder. Though if you jump the switch out and it works that's another way to check.
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Joined: Apr 2015
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From: Phoenix, AZ
Car: 1987 Firebird Formula
Engine: 305 TPI
Transmission: T-5
Re: Reverse Lights Short?
Ok thanks. So here's what I'm thinking: the switch has two terminals, so if I put the shifter in reverse, disconnect the pigtail from the switch, and use the ohmmeter to probe from the terminals to the trans housing, a closed circuit would indicate a short in the switch. In other words, neither terminal should be grounded when disconnected. Does that sound right?
So did you replace the switch or were you able to make a repair? I'm concerned if it's a faulty switch, as mine is only a few months old and has probably about 300 miles on it.
Thanks
So did you replace the switch or were you able to make a repair? I'm concerned if it's a faulty switch, as mine is only a few months old and has probably about 300 miles on it.
Thanks
Thread Starter
Junior Member
Joined: May 2016
Posts: 17
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From: Conshohocken, PA
Car: 1985 Pontiac trans-Am
Engine: 305
Transmission: T5
Axle/Gears: 3.27 9 bolt
Re: Reverse Lights Short?
If you don't want to use a jumpper wire on the harness side, or even jump it with the dmm, you can put it in reverse & do a continuity check between the terminal and the block. I bought a new switch at autozone for $11, but it just failed again. They's a possibility I got a bad switch, so I may try another, but I'm starting to think the trans is breaking the switch some how.
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Joined: Apr 2015
Posts: 15
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From: Phoenix, AZ
Car: 1987 Firebird Formula
Engine: 305 TPI
Transmission: T-5
Re: Reverse Lights Short?
If you don't want to use a jumpper wire on the harness side, or even jump it with the dmm, you can put it in reverse & do a continuity check between the terminal and the block. I bought a new switch at autozone for $11, but it just failed again. They's a possibility I got a bad switch, so I may try another, but I'm starting to think the trans is breaking the switch some how.
Thread Starter
Junior Member
Joined: May 2016
Posts: 17
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From: Conshohocken, PA
Car: 1985 Pontiac trans-Am
Engine: 305
Transmission: T5
Axle/Gears: 3.27 9 bolt
Re: Reverse Lights Short?
I haven't been able to fund anything on t5 reverse circuits, which is why I initially started this thread. Best guess is if not cheap parts, maybe what ever presses the reverse light in is crushing something internally, so that the feed side is crushing into the metal. I wish I kept the old switch so I could dissect it. Maybe I'll do that with the next, unless you beat me to it.
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Joined: Apr 2015
Posts: 15
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From: Phoenix, AZ
Car: 1987 Firebird Formula
Engine: 305 TPI
Transmission: T-5
Re: Reverse Lights Short?
I will see what I can come up with on a dissection. I didn't notice any increased shifting resistance when going from no switch (freeze plug in housing) to installed switch, so It's not like I'm crushing the thing. If that is the problem, then I guess the solution is to use a washer so that the switch is just barely actuated.
What type of transmission fluid are you using? I know the debate rages about what is best, I am using ATF. I am wondering if the wrong fluid may be responsible for switch failure. Long shot, I know.
What type of transmission fluid are you using? I know the debate rages about what is best, I am using ATF. I am wondering if the wrong fluid may be responsible for switch failure. Long shot, I know.
Joined: Aug 1999
Posts: 5,259
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From: RI
Car: 1984 Camaro Berlinetta
Engine: LT1
Transmission: T56 6-speed
Axle/Gears: 4.11 LS1 Rear End
Re: Reverse Lights Short?
The 85 should have a small plug near C207,... it's called C221 and has about 6 terminals. The reverse llight wires MIGHT be run thru this smaller plug because your car is a TPI T5. ( not a carb T5 )
* C207 is the large pair of wiring plugs that connect the dash harness to the ECM harness under the pass side of the dash. C221 is located right next to them.
Here Ya' Go,........
Hope that helps !
* C207 is the large pair of wiring plugs that connect the dash harness to the ECM harness under the pass side of the dash. C221 is located right next to them.
Here Ya' Go,........
1985 C207
PIN Color From / To (Notes)
A Brn ALDL (pin C) / ECM (AIR control)
B* Dk Blue BU Fuse / Back Up Switch ( V8 T5 )
B* Red ALDL / Fuel Relay ( V6 - TPI )
B* Org/Blk FP FUSE / Fuel Relay ( L4 )
C* Brn/Wht ECM / CE Light ( L4- V6 - TPI )
C* Wht/Grn Light Driver / ECM ( LG4 & L69 )
D* Blk/Org FP/INJ fuse / Fuel Relay ( L69 )
D* Tan/Wht Fuel Relay / Fuel Pump ( V6 )
D* Lt Blue Fuel Relay / Fuel Pump ( TPI )
D* Tan Oil Pr Sensor / Oil Pr Gauge ( L4 )
E Wht/Blk ALDL / ECM (test)
F Pnk/Blk IGN fuse / EGR-ECM
G* Dk Grn BU Fuse / Back Up Switch ( V8 T5 )
G* Pnk/Blk Gage Fuse / MAF Relay ( V6)
G* Pnk/Blk Gage Fuse / Burn Off Relay ( TPI )
G* Pnk/Blk Gage Fuse / Air Cond Relay ( L4 )
H Tan/Blk ALDL / TCC-ECM
J* Ppl Starter / Fuel Relay ( L69 )
J* Org ALDL / ECM ( L4 - TPI )
K Brn ECM / VSS
L Tan/Wht Fuel Relay / Fuel Pump ( L4 - L69 )
M Blk/Wht VSS,P/N switch / Grd
N Org/Blk ECM / P/N switch
P Ppl Brake / TCC
R Ppl/Wht Crank Fuse / Cold Start-ECM ( V6-L4 )
Plug C221
A Pnk/Blk Inj2 Fuse / Even Fuel Injectors
B Lt Green Back Up Switch / BU Lights ( V6-T5 )
C Brn Fuel Pump-Fan Fuse / Fan Relay ( V6 - TPI )
D Pnk/Blk Inj1 Fuse / Odd Fuel Injectors
E
F Dk Blue Back Up Fuse / Back Up Switch ( V6-T5 )
PIN Color From / To (Notes)
A Brn ALDL (pin C) / ECM (AIR control)
B* Dk Blue BU Fuse / Back Up Switch ( V8 T5 )
B* Red ALDL / Fuel Relay ( V6 - TPI )
B* Org/Blk FP FUSE / Fuel Relay ( L4 )
C* Brn/Wht ECM / CE Light ( L4- V6 - TPI )
C* Wht/Grn Light Driver / ECM ( LG4 & L69 )
D* Blk/Org FP/INJ fuse / Fuel Relay ( L69 )
D* Tan/Wht Fuel Relay / Fuel Pump ( V6 )
D* Lt Blue Fuel Relay / Fuel Pump ( TPI )
D* Tan Oil Pr Sensor / Oil Pr Gauge ( L4 )
E Wht/Blk ALDL / ECM (test)
F Pnk/Blk IGN fuse / EGR-ECM
G* Dk Grn BU Fuse / Back Up Switch ( V8 T5 )
G* Pnk/Blk Gage Fuse / MAF Relay ( V6)
G* Pnk/Blk Gage Fuse / Burn Off Relay ( TPI )
G* Pnk/Blk Gage Fuse / Air Cond Relay ( L4 )
H Tan/Blk ALDL / TCC-ECM
J* Ppl Starter / Fuel Relay ( L69 )
J* Org ALDL / ECM ( L4 - TPI )
K Brn ECM / VSS
L Tan/Wht Fuel Relay / Fuel Pump ( L4 - L69 )
M Blk/Wht VSS,P/N switch / Grd
N Org/Blk ECM / P/N switch
P Ppl Brake / TCC
R Ppl/Wht Crank Fuse / Cold Start-ECM ( V6-L4 )
Plug C221
A Pnk/Blk Inj2 Fuse / Even Fuel Injectors
B Lt Green Back Up Switch / BU Lights ( V6-T5 )
C Brn Fuel Pump-Fan Fuse / Fan Relay ( V6 - TPI )
D Pnk/Blk Inj1 Fuse / Odd Fuel Injectors
E
F Dk Blue Back Up Fuse / Back Up Switch ( V6-T5 )
Thread Starter
Junior Member
Joined: May 2016
Posts: 17
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From: Conshohocken, PA
Car: 1985 Pontiac trans-Am
Engine: 305
Transmission: T5
Axle/Gears: 3.27 9 bolt
Re: Reverse Lights Short?
I'm not sure which fluid is in it, I know they are supposed to have Dexron ATF in them. It is theoretically possiible the Liquid is doing something to the rubber inside, but I am unsure, and still haven't picked up a new switch. Have you had any luck?
My 85 is Carbed, I sadly have the Rochester Quadrajet e4m. Hopefully oneday I can do an LSx/T56 swap, but right now I don't have the money to do anything more then maintain my Bike and TA
My 85 is Carbed, I sadly have the Rochester Quadrajet e4m. Hopefully oneday I can do an LSx/T56 swap, but right now I don't have the money to do anything more then maintain my Bike and TA
Junior Member
Joined: Apr 2015
Posts: 15
Likes: 0
From: Phoenix, AZ
Car: 1987 Firebird Formula
Engine: 305 TPI
Transmission: T-5
Re: Reverse Lights Short?
Haven't done it yet. Had some wires melting under the hood due to previous owner's DIY electrical shenanigans. Perhaps this week I'll try to sort it out.
Thread Starter
Junior Member
Joined: May 2016
Posts: 17
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From: Conshohocken, PA
Car: 1985 Pontiac trans-Am
Engine: 305
Transmission: T5
Axle/Gears: 3.27 9 bolt
Re: Reverse Lights Short?
I've had a new reverse switch in for almost 2 weeks now. Seems to still be working. I slightly tested the old new sensor and found neither terminal was shorted to the body until the ball made contact. I haven't opened it, I'm trying to determine if I want my $11 back. Have you straightened out your electrical project?
Junior Member
Joined: Apr 2015
Posts: 15
Likes: 0
From: Phoenix, AZ
Car: 1987 Firebird Formula
Engine: 305 TPI
Transmission: T-5
Re: Reverse Lights Short?
I've had a new reverse switch in for almost 2 weeks now. Seems to still be working. I slightly tested the old new sensor and found neither terminal was shorted to the body until the ball made contact. I haven't opened it, I'm trying to determine if I want my $11 back. Have you straightened out your electrical project?
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