Troublesome rear turn signal voltage. (1 Viewer)

[krispy]

Hi all, I am working on the rear tail lights. My 40 is a late 77 build. I bought an aftermarket replacement set from SOR and had to replace the connectors on the units with the ones off my trashed old tail lights. In the process, I also removed an old trailer brake system and some very chewed-up wiring.

Here's where I'm at today. I think I've identified all the positions on the harness side of the connection. Let me know if you think my understanding is off. (FYI, the alligator clip in the photo is a ground test, so I don't have to hold the multimeter lead.

However, when I activate the turn signal im only getting rotating 7.5 to 7.9VDC

Running lights are giving me roughly 12V; I get approximately 12 when I actuate the brake pedal too. I cant test reverse since i dont have the shift lever in but the turn signal is stumping me. Im getting the same level of voltage on both sides. Other relevant info is:

The front signal is blinking.

The hazard switch does not work, I cant recall if it ever did? When i pull the switch on i get a short burst of light on the drivers side signal in the cluster thats it. Not sure if its related, or the switch is bad or...

A couple of videos of the voltage fluctuation and front signal.

Also, I did replace everything with LEDs. At first, I thought it might be a resistance issue, but with the front ones working, that doesn't seem valid.

thanks for the help!

 

[aging fleet]

Does the voltage change if you move the alligator clip to a different ground location?

After that, I’d start working upstream to see if you can find where it drops from 12 to 7v. When I had an issue with my drivers side reverse light I was getting a ton of resistance through the circuit, it ended up being corrosion at the plug.

 

[Pighead]

IIRC, sometimes the turn signals use the emergency flasher to flash. You might find that box, see if you can take it apart and clean the contacts

 

[Engineer8000]

Are you getting the same voltage at the front turn signal lights?

If so the problem is in the power source. The power for the turn signals is fed through the hazard switch (GR wire). Sounds like that may be a place to check. I've heard of people having to rebuild their hazard switches on here. Could also be a corroded fuse holder or turn signal switch.

If you are getting battery voltage to the front signals and only 7.5 to the rear, then it is probably in the rear chassis harness, maybe the connector at the fire wall.

 

[B y r o n]

When you said you did everything in LED's, did that include the flasher unit?

 

[charliemeyer007]

Some voltage meters are better than others. The flasher needs a certain amount of resistance to heat the circuit enough to blink. Weak wires in the front might provide that resistance, the wires to the back might have too much or two little. Then there is the ground issues - add a ground wire to every socket and make sure it electrically leads to the - on the battery.

 

[Engineer8000]

Good point. Usually with LEDs, they do not draw enough current to heat up the bimetallic strip in the old-style flashers. The fact the fronts are flashing tells me that is working ok, maybe slow though. Some of the smarter flashers see them as too high a resistance and will flash fast indicating it thinks there is a blown bulb. What type of flasher do you have? You definitely want a flasher for LEDs to rule out issues there.

 

[krispy]

Does the voltage change if you move the alligator clip to a different ground location?

After that, I’d start working upstream to see if you can find where it drops from 12 to 7v. When I had an issue with my drivers side reverse light I was getting a ton of resistance through the circuit, it ended up being corrosion at the plug.

No, I tried that, but it stays the same. I also get good voltage at that location to the other circuits coming into that connector (breaks and running lights)

IIRC, sometimes the turn signals use the emergency flasher to flash. You might find that box, see if you can take it apart and clean the contacts

Thats a good idea. Is that the same as the hazard switch? If not, where is that box?

Are you getting the same voltage at the front turn signal lights?

If so the problem is in the power source. The power for the turn signals is fed through the hazard switch (GR wire). Sounds like that may be a place to check. I've heard of people having to rebuild their hazard switches on here. Could also be a corroded fuse holder or turn signal switch.

If you are getting battery voltage to the front signals and only 7.5 to the rear, then it is probably in the rear chassis harness, maybe the connector at the fire wall.

I didnt think to check the voltage at the front signals, they work so my brain moved past it. But good idea ill check. I'll need to inspect the harness moving back and see if there's something wonky. Just so im certain im reading this right:

When you said you did everything in LED's, did that include the flasher unit?

What do you mean the flasher unit, do you mean the relay? All the bulbs are replaced with LEDs.

Some voltage meters are better than others. The flasher needs a certain amount of resistance to heat the circuit enough to blink. Weak wires in the front might provide that resistance, the wires to the back might have too much or two little. Then there is the ground issues - add a ground wire to every socket and make sure it electrically leads to the - on the battery.

My multimeter is a pretty nice Fluke one, it hasn't failed me yet, but I suppose it could be giving some weird readings. Do you mean add jumper from the neg battery post and test the voltage at the rear harness points?

Good point. Usually with LEDs, they do not draw enough current to heat up the bimetallic strip in the old-style flashers. The fact the fronts are flashing tells me that is working ok, maybe slow though. Some of the smarter flashers see them as too high a resistance and will flash fast indicating it thinks there is a blown bulb. What type of flasher do you have? You definitely want a flasher for LEDs to rule out issues there.

I had an OEM flasher relay in there; it didn't work at all. Then I used a newer one, though likely still 20 years old, I had lying around. That's when the fronts came alive. I'll do some reading about newer relays designed for LEDs. That was a good call, and they're pretty cheap.

Thanks all for the suggestions! Before this issue, I spent some time cleaning corrosion off all terminals on the main fuse block. I used the two rear spades for a triggered and constant 12V to an alt power distribution block I built. It didn't work at all until I gave the posts a good cleaning. I will definitely do that to the hazard switch. What's the preferred method for getting that out of there? The closest access I see is the hole for the radio.

 

[charliemeyer007]

Fluke is a good brand. I had to learn Fluke DOS back at the university for data logging and PID control.
Any meter dropped enough can go out of calibration. Pays to check them once in a while.

The bulb socket is usually grounded to the sheet metal its attached to. Age is usually accompanied by corrosion on the surface of the sheet metal, the mounting stud/nuts. I tend to drill and tap the metal socket housing and run a ground wire to the neg battery terminal. Some I have just added a ring terminal to the attaching bolt and runt that wire to ground.

 

[krispy]

Fluke is a good brand. I had to learn Fluke DOS back at the university for data logging and PID control.
Any meter dropped enough can go out of calibration. Pays to check them once in a while.

The bulb socket is usually grounded to the sheet metal its attached to. Age is usually accompanied by corrosion on the surface of the sheet metal, the mounting stud/nuts. I tend to drill and tap the metal socket housing and run a ground wire to the neg battery terminal. Some I have just added a ring terminal to the attaching bolt and runt that wire to ground.

Gotcha, ya that makes sense, I've been extending new grounds from good points on the frame that are then tied to the neg terminal. Im a power distribution electrical engineer by trade. While at work, im pretty experienced, but I find when im home, all my knowledge and experience eludes me at first, then i sleep on it and smack my forehead for being an idiot!

 

[charliemeyer007]

I was talking with my Sis yesterday about her dead laptop. Checking to see if the charger is making power with a VOM is too hard - I taught her to use the VOM several years ago for both voltage and wire continuity but I guess that skill set is now dormant, and she doesn't remember what the meter look like or where it went. I made up a electrical bucket, a plumbing bucker, a picture hanging bucket, a range bucket. Each bucket had all the tools needed for the task such as changing a switch/outlet, hose gasket, cleaning rod, bag for spent brass, ear plugs, safety glasses, marking pen...

 

[krispy]

I was talking with my Sis yesterday about her dead laptop. Checking to see if the charger is making power with a VOM is too hard - I taught her to use the VOM several years ago for both voltage and wire continuity but I guess that skill set is now dormant, and she doesn't remember what the meter look like or where it went. I made up a electrical bucket, a plumbing bucker, a picture hanging bucket, a range bucket. Each bucket had all the tools needed for the task such as changing a switch/outlet, hose gasket, cleaning rod, bag for spent brass, ear plugs, safety glasses, marking pen...

Thats a good idea i need to do that for my friends whos house im always at fixing stuff.

 

[B y r o n]

Hazard/Turn Signal Flasher requires a current load to function properly. Newer flasher units are digital and don't require a load so they work with LED's which produce minimal load. As you mentioned, they are cheap so start there before spending money on more expensive components that may not need replacing.

 

[pb4ugo]

To get to the switch you can remove the ash tray for some access and vision. The heater duct under the dash is held in place with 2 screws. It's very easy to remove and should give you some more access. I think the knob has a set screw then it unscrews. The escutcheon/nut is a little more difficult to remove and you'll probably have to hold the switch on the back side while loosening the nut.

 

[Engineer8000]

Yes you are correct about the items on the schematic. The hazard switch has 2 power sources, one for the turn signals and one for the hazards.

 

[krispy]

Yes you are correct about the items on the schematic. The hazard switch has 2 power sources, one for the turn signals and one for the hazards.

Great thanks! Does anyone know the easiest way to access/remove the hazard pull switch so I can clean it up and hit it with detox-it before I spend money on a new one?

 

[pb4ugo]

Great thanks! Does anyone know the easiest way to access/remove the hazard pull switch so I can clean it up and hit it with detox-it before I spend money on a new one?

Post #14

To get to the switch you can remove the ash tray for some access and vision. The heater duct under the dash is held in place with 2 screws. It's very easy to remove and should give you some more access. I think the knob has a set screw then it unscrews. The escutcheon/nut is a little more difficult to remove and you'll probably have to hold the switch on the back side while loosening the nut.

 

[krispy]

s***, I totally missed your response! Thank you!

 

[pb4ugo]

To remove the escutcheon nut you can try a 90* or 45* snap ring pliers in the 2 holes or carefully use pliers trying not to scuff the nut to badly.

 

[charliemeyer007]

Maybe use an oiler rod and work some Kroil into the escutcheon nut/fitting and let it work for a day or two. Spraying some PB Blaster under the dash on the back side of the switch could help also.

Hacking the switch - work in a clean well lighted work area will help - a big cardboard box with plastic wrap across the top and a good desk light pointing in. Cut some hand holds in the side. Bend the locking open as little as you can to get the switch apart - they are fragile will break off easily - same with crimping them shut. There be spring loaded parts inside like contacts and detent balls. You might try just hosing it out with electric contact cleaner if flying parts spooks you.

Go to a junk yard and pull a lot of switches headlight, fans etc - take them apart to see how they work and put them back together. Maybe there are youtube vids for switch hacking.

Polishing contacts to get them clean is better than filing/grinding them which can remove a plated surface and they will corrode again sooner. Chiropractic work might be needed to straighten long contacts or coil/leaf springs