rear tail lights wiring help

[cjoenny89]

I just installed the wire harness on the back of the truck to get the tail lights and side markers working. I fixed the wire harness at work and installed some better light housings. I hooked up 12 volts and tested the wiring and it was all good,
Brown wire is running lights and that works for side markers, tail lights, and license plate. I also get the blinkers to work.
Left back up light blinks on then off for a quick second when I put the truck in reverse. I am going to make sure I have a good ground on the right back up light tomorrow.
I am wondering is there an adjustment for the reverse light and if so where is it located?
Also I don't have any brake lights. what tells the brake lights to turn on? Is it that single wire under the hood on the proportioning valve that turns on the brake lights? My Brakes are not working good and that is my next issue work on they also might be low on fluid,
so what and where is the reverse switch?
and what turns on the brake lights?
Thanks
Chad

[FirstOwner69]

Assuming you have an automatic...

There is a switch (neutral safety switch) mounted to the top of the steering column a few inches inside the firewall. There is a small screw on each end. You can adjust the timing of the backup lights by loosening the screws and rotating the switch from side to side. It takes very little change of position to adjust the lights. However, if one side works and the other doesn't, it does not sound like the problem is the switch. My bet would be on the ground. The switch also prevents the starter from being energized in any positions other than park or neutral.

The brake light switch is under the dash in contact with the brake pedal arm. It can also be adjusted fore and aft to change its engagement point. The single wire on the prop valve (or distribution block pre 1971) turns the brake light on the dash if there is a brake system malfunction.

[cjoenny89]

I am sorry it's a 3 on the tree 1968 c20. I just put my wire harness back on after being off the truck for 25 plus years and recent paint job. Today i ohmed out the wire harness and it was all good. I have to check for power at the other light but I think I didn't get a good connection on the back up light quick connect or I have a bad ground. Reguardless if I slam the shifter in rev. The one back up light turns on then off. Is there an adjustment for it on the 3 speed? I will check the brake light wiring tomorrow.

[LockDoc]

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In addition to what FirstOwner said, make sure you have a ground wire from the frame to the bed.

LockDoc

[FirstOwner69]

Originally Posted by cjoenny89

I am sorry it's a 3 on the tree 1968 c20. I just put my wire harness back on after being off the truck for 25 plus years and recent paint job. Today i ohmed out the wire harness and it was all good. I have to check for power at the other light but I think I didn't get a good connection on the back up light quick connect or I have a bad ground. Reguardless if I slam the shifter in rev. The one back up light turns on then off. Is there an adjustment for it on the 3 speed? I will check the brake light wiring tomorrow.

I believe the 3 on the tree switch is also on the column. Probably adjusts in a similar fashion.

[FirstOwner69]

Start at post 5 in this thread.
http://67-72chevytrucks.com/vboard/s...d.php?t=589842

More here:
http://67-72chevytrucks.com/vboard/s...d.php?t=430056

EDIT: Also, regarding the brake light switch, the switch is in the off position when the button is depressed by the brake pedal arm and on when the button is out/not in contact with the arm. Sort of the reverse of what seems logical.

[cjoenny89]

I got the Rev lights to work thanks I adjusted the switch on the column. I also found out that the back switch is bad and isn't popping up when you push the brake pedal. I jumpered the wire and the lights come on. I am hoping to get a new switch tonight. Thanks for all the help.