My backup lights don't work on my 79. It's not the bulbs as I've tried that, and all other tail lights and brake lights work fine. Where do I start?

 

FUSE for one...either blown or not flowing 12 volts through it due to being dirty or corroded...which can happen if your firewall area is leaking water...as they can do..as we all know.

If you can not get power to the center terminal in the socket. it may be in your neutral safety switch...or the wiring harness connector over by your hood release/fuse panel that feeds current to the rear of the car...or the grounds in the sockets are bad.

I believe the wire is a light green.

DUB

 

Mine don't either... I've heard there's a switch under the center console that is near the shift linkage to look at... Can remove the side trims on the console to get to it... Just remove the bottom seat cushion on one side temporarily to get at the screw that holds it in place ... Perhaps I should go look at mine too... ;-)

 

Too many wires under there on the drivers side... Gonna try the passenger side access and see if I have better luck...

 

let me know if you figure anything out. I won't have time to look until later in the week

 

Here's what I found while looking at the right side of my shifter linkages...
When in neutral both the arrows line up , so I'm good for adjustment I would suppose... Haven't traced any of the wires yet looking for issues... Is this unit what will turn on my backup lights? Is it cleanable/adjustable/or just replaceable?

 

Reading my troubleshooting section of my shop manual now...

 

I should mention that my backup lights don't work and I have a manual transmission. I'm sure that there is a difference between how the reverse lights on a auto and manual work.

 

Looking through the shop manual , yours should be easier... It's like a brake pedal switch, just in the reverse gear... It's under your console , near the front .. Make sure it's making contact with the shift linkage...

 

Yep. For AT cars, backup lamps are included in the neutral safety switch on the shifter. For standard trans cars, the backup light switch mounts underneath on the tranny and plugs into a harness coming down from the firewall.

 

Your back up switch is attached to the transmission. See if the switch is good and the little rod is not out of adjustment and that you have 12 volts to the switch with the key on and the shifter in reverse.

 

FireballXL5
Power (12 volts) should be on the PINK wire in your photo when the key is ON...and when you put the shifter in reverse...the light green wire should get 12 volts.

DUB

 

Thanks! I've got more than just this issue to diagnose and solve... Appreciate the feedback... Thought I was helping the OP... But he's a manual trans... I will look into it next time I wrench... Much appreciated.

 

OP is the same thing.
My 74 manual has the backup switch under the car. Same pink and green wires.
I believe what was said is correct pink is the supply power to the switch green is to the lights.

I also have (google is you wish) a powerprobe III. Nice little toy. Basically a voltage reader (multi meter/dvom that reads only voltage) showed 12 to the switch, then I was able to power the wire to the lights. (powers or grounds)
This turned my lights on.

Same idea as stated before check for power to the switch, then power out of the switch. I did not have power out, with my power probe I was able to supply that power (safely, has a circuit breaker) and turn my lights on. So all of my wiring is good, both light bulbs.
If you feel like it you can match the amperage with an inline fuse and power it straight from the battery. (the fuse gives you the safety over just a piece of wire)
That will tell you if everything is good other then the switch.

Going to add a bit.
Check power to the bulb first. Relatively easy to get to. Check the bulbs too.
If you have power/good bulbs, check the ground.
If you have no power to the bulb, check the switch. If now power out of the switch, check the power to the switch.
Keep in mind to test the switch you need to be in R key on.
If not a switch/bulb you will need to find the bad ground/break in a wire.

 

So... Finally checked the wires for power at that switch on my automatic... The green and pink on the left have good power going in... On the right side the top purple-white doesn't get power, and the purple on the bottom gets a very weak light from the tester and I hear a click/ pop from somewhere near/ in the switch... Dunno if I just need to clean it or what... Didn't have the time to remove it today ... Any advice, and more testing tomorrow... ;-)

 

The only wires you should be worrying about are the pink and light green. Pink should be 12 volts with the key on...if not...then look at your fuse for the back-up lights. WHEN the shiftier is placed in reverse..the light green wire should then get 12 volts...if not...it may be in the switch or its adjustment.

The purple wires do not mean anything for your reverse light issue...they are for your starter.

If you get 12 volts out of the switch ON THE LIGHT GREEN WIRE...and your reverse lights do not work....go to the rear and check the center terminal after you have removed a bulb and see if you are getting 12 volts there...if you are..then check the ground terminal inside the socket also.

IF you are not getting 12 volts on the center terminal in the light socket...then you may want to check the connector over by your fuse panel and hood release handle and check if you are getting 12 volts going through it on the light green wire.

DUB

 

Many thanks dude! At work now, will troubleshoot more tomorrow.

 

NO PROBLEM...One thing to ALWAYS keep in mind.

Even though you can test a circuit and get 12 volts ( for example)...and for some odd reason the item you are wanting to get to work DOES NOT WORK...just remember...that just because it has 12 volts....kinda means nothing at all....and this is because what is trying to work...(a light for example) REQUIRES AMPS to get it to work.

And if the terminals in your connectors are badly corroded or very dirty...or are weak in pinch strength...were the terminals are loose when touching...you will get 12 volts...but the poor connection will prevent the amps to allow the part to work. It is like a loose battery cable...everything works when you turn the key on...but when you go to crank the engine...the engine will NOT crank because the loose connection will not allow the amount of amps needed to crank your engine to flow as designed.

ALSO...using an ohmmeter, or voltmeter to test a circuit will let you know that the wire is continuous. But that again is only ONE PART of the equation. As I have written before. if you have a wire that has 20 strands that make up the wire so it can carry an amp load for "whatever". And out of those 20 strands...18 of them are broken. When testing with a volt/ohmmeter...it will show the wire to be GOOD...and it is....BUT it is NOT when trying to carry the amp load needed.

SO...if you feel you have a circuit that is "suspect" and needing quick test to verify that it can carry a load of amps. I use a halogen headlight...and wire it so the high/low beams will come on when I ground it and give it power. I connect the power wire of the headlight to my circuit in "question"...ground the headlight as needed and then supply power to eh other end of the circuit in "question" that I connected to the headlight. If the headlight works and is bright...the I know the wire is GOOD...if it does not...then I know the wire has an issue somewhere. You would be amazed on how many wiring issue I have to deal with are solved by using this home-made test tool.

DUB

 

Hahahahaha!!!! Bubba, in his infinite wisdom, put 1157 bulbs in the reverse light location instead of 1156 bulbs! Problem solved... Scratch that one off the 'to do' list... Lol

 

Glad to read it...I wish all repairs could be so simple.

DUB