Electrical questions (backup lights)

RDHOG

New Member
Joined
Feb 16, 2022
Messages
15
Reaction score
14
Location
New Hampshire
I have a 1969 300 with no back up lights. Can someone explain where the 12v comes from with the key on and car in reverse shouldn't I have 12v at the neutral day switch? Am I correct that the you should also get continuity thru the sock and light housing so it gets a body ground. One last question the plug for these back up lights on the car side is male and the light side is female. I get no power. But on the plate light it is opposite. The female plug is on the car side and I get 12v there. Oh one more question the neutral safety switch is to three wire and is new. Thank you for any help

20220623_082034.jpg


20220623_082045.jpg


20220623_082039.jpg
 

Ross Wooldridge

Senior Member
FCBO Gold Member
Joined
Apr 25, 2016
Messages
4,783
Reaction score
4,079
Location
Scotland, Ontario, Canada
If I am correct, the 12 power is sent to the backup lights from the neutral safety switch, which is found on the driver side of the trans. I believe the NSS gets its 12V feed from a key-on ignition source - there should be 3 wires at the NSS - one to the backup lights, one a 12V feed, and the third being the grounding wire from the the starter relay, on the ANGLED connector tab found on the bottom corner of the relay (found on the firewall or inner fender). The 12V feed CANNOT flow to the backup lamps if the comb inside the transmission is not pushing the ball into the switch and completing the circuit. There are 3 steps to the ball's positioning based on detents/bumps on the comb - see below.

1 will not engage the switch, so no current flow anywhere, and the car won't start. This will be in every position BUT reverse.
2 is going to give you current flow to the backup lights, but NOT ground out the start relay to permit the starter to engage.
3 is going to engage the relay only to permit the starter to engage, but not send 12V to the backup lamps.

Unless you're in Park or Neutral, the comb will not engage the NSS, and no start and no 12V to the backup lights.
There will be 2 identical steps on the comb - Park and Neutral.
There will be 1 unique detent on the comb - reverse lights. This is the ONLY position that 12V will be found on 2 wires (if the switch is working properly).

I think I have that right, but others will please chime in to correct me. Regardless, look for power coming to the switch from a key on source, a wire running to the start relay, and a wire running to the backup lamps.

Putting 12V to the wire running from the Neutral Safety Switch to the backup lamps should make them light up, provided the lamps have a good ground at the housing.
Connecting the key on hot 12V feed to the wire running to the backup lamps (bypassing the NSS) should make them light up, provided the lamps have a good ground at the housing. If this happens, then you likely need a new NSS.
 

RDHOG

New Member
Joined
Feb 16, 2022
Messages
15
Reaction score
14
Location
New Hampshire
Ross
Thanks for taking the time to answer my questions. I am working on getting the grounds cleaned I am having a problem with the light socket not making a connection they the housing. Tonighti will see if I have 12 v in the NSS plug. I fixed the ground from the NSS to the starter relay that works now. No luck with the back up lights yet I will research the comb in the transmission.
 

thethee

Well-Known Member
Joined
Feb 13, 2021
Messages
904
Reaction score
983
Location
Netherlands
FYI, with the three prong NSS, the outer two wires are for the backup lights and the centre wire is for grounding the starter relay.
 

1970FuryConv

Old Man with a Hat
Joined
Aug 8, 2014
Messages
5,170
Reaction score
4,661
Location
Richmond, VA
I have a 1969 300 with no back up lights. Can someone explain where the 12v comes from with the key on and car in reverse shouldn't I have 12v at the neutral day switch? Am I correct that the you should also get continuity thru the sock and light housing so it gets a body ground. One last question the plug for these back up lights on the car side is male and the light side is female. I get no power. But on the plate light it is opposite. The female plug is on the car side and I get 12v there. Oh one more question the neutral safety switch is to three wire and is new. Thank you for any help
1 With the key on and car in reverse shouldn't I have 12v at the neutral safety switch? Yes, at the output wire for reverse lights
2 Am I correct that the you should also get continuity thru the socket and light housing so it gets a body ground? Yes
3 But on the plate light it is opposite. The female plug is on the car side and I get 12v there? Plate light comes on with taillights and has nothing to do with reverse lights.
4 Oh one more question the neutral safety switch is to three wire and is new? see previous post
 

RDHOG

New Member
Joined
Feb 16, 2022
Messages
15
Reaction score
14
Location
New Hampshire
Update spent a good part of yesterday working on the back to lights. First there were multiple ground issues with the back up lights housings. I corrected them. I also wasn't getting 12v to the NSS checks all the wires and found a bad connection on the fire wall. Last but not least the NSS treads in to far.I had two other switches from 2 different companies one was a little shorter than the other so between the shorter switch and I added a extra washer from the other NSS voila working back up lights. Thanks for all the help here
 

1970FuryConv

Old Man with a Hat
Joined
Aug 8, 2014
Messages
5,170
Reaction score
4,661
Location
Richmond, VA
Update spent a good part of yesterday working on the back to lights. First there were multiple ground issues with the back up lights housings. I corrected them. I also wasn't getting 12v to the NSS checks all the wires and found a bad connection on the fire wall. Last but not least the NSS treads in to far.I had two other switches from 2 different companies one was a little shorter than the other so between the shorter switch and I added a extra washer from the other NSS voila working back up lights. Thanks for all the help here
Great work! Glad to hear: Problem solved.
 

thethee

Well-Known Member
Joined
Feb 13, 2021
Messages
904
Reaction score
983
Location
Netherlands
Very nice, finding and fixing electrical problems is one of the most satisfying things there is IMO!
 
Top