Headlights, tail lights and turn signals

[timberrrrrr]

Since I purchased my M1078 the headlights, tail lights and turn signals haven't worked (or at least I haven't been able to figure them out). The truck has mostly been in the shop since purchase having various fun stuff added to it (dump frame with winch, started overland camper build, etc) so I haven't driven around much.

It's about time to figure out the lights. I just removed all of the breakers in the dash and replaced them with fuses, thinking it would be easier to find a bad fuse than a bad breaker. I was hoping the breakers were going to be the issue, but no luck there. I do have power to the fuses that supply the lights, etc.

I have moved the black out switch to service lights and panel brights, but no luck.

Is there something I am missing?

 

[NDT]

Are the proper part number relays in each position? They are listed on the PDP cover. Uncle gets this wrong all the time.

 

[timberrrrrr]

I don't know if the correct relays are there. My cover doesn't have anything on it.

I downloaded the spec sheet identifying the relays and fuses.

I went through the relays to confirm the correct number of pins were on each one according to the spec sheet, and they were correct.

I guess the next step would be purchasing some new relays to try out?

 

[NDT]

Number of pins AND voltage.

 

[timberrrrrr]

Right, forgot to confirm the voltage was correct on all of them. Will have another look.

Looking around the forum on this subject, it was pointed out by Superman that you can use 5 pin spdt, for all of them and forget about the 4 pin spst relays. the extra leg/pin doesn't matter and makes things more confusing. Just ordered a bunch of 12v and 24v spdt for spares and to replace what may be misplaced in my panel.

Hopefully this will solve the problem

Thanks for the help!

 

[coachgeo]

Im guessing issue is front of truck wire harness... probably where it goes thru the holes into the dash or into the Power Distribution Panel (PDP). Is this truck an A1? there is mentions of bad PDP circuit boards on the early era of the A1's

 

[timberrrrrr]

Mine is an A0

 

[timberrrrrr]

Finally back to work on the truck.

Replaced all fuses and relays, still no lights, turn signals, brake lights, hazards

When I purchased the truck at auction, their report showed a picture of the headlights working. I had the truck shipped to me and haven't driven it other than to get it home and to work on it with misc test drives.

I have the selector switch turned to service drive and the auxiliary lever to panel bright. I have tried all of the other settings as well

It must be something simple that I am missing.

Thoughts?

 

[branr1]

Check all your grounds, do you have power at the switch? Cut the circuit in half and work toward the issue. Power at the switch work toward the lights no power work toward the fuse panel.

 

[Ronmar]

Because of the way the schematic is layed out, it might be better to pick just one issue like headlights and run it down completely. You might find doing this solves the other problems when you find an issue in common. I had a bunch of issues, running thru one circuit led me to a loose connector on the back of the idiot light panel. Reconnecting this fixed all the other issues...

For headlights:

12V flows from the 12V test point X1 on the Power Distribution Panel(PDP), thru CB70 to the lightswitch pin F. It also goes to the ignition switch so if it starts/runs you probably have power this far. It leaves the light switch on pin M when the headlights are turned on and goes to energize the headlight relay K7(pin 86) so you should be able to feel/hear K7 click when you turn on the headlight switch. If not pull K7 and check for 12V to ground at pin 86. If not look for it at pin M on the lightswitch.

All the relays work the same. Pin 85 connects to ground and when you apply voltage to pin 86 it should energize. Switched power is applied to pin 30 and it leaves on pin 87A when the relay is de-energized or pin 87 when the relay is energized. So if a relay wont energize with voltage available at pin 86, check for a path to ground on pin 85 first by measuring for a low resistance between pin 85 and the ground test point X3 on the PDP. A quicker check is if you have system voltage to ground on 86, move your negative test lead to 85 and you should also see system voltage if pin 85 has a good path to ground.

Headlight power comes from X1 thru CB78 to K7-30 it leaves on K7-87 when K7 energizes. It travels to the high/low beam relay K8-30 and leaves on either 87A or 87 depending on high/low beam setting. If you have power at pin K8-30 either high or low beam should be energized with a good relay plugged into the K8 slot.

A handy tool to have are a couple of pieces of wire with relay sized spade connectors on each end. You can use these to bypass suspect relays and power circuits in a pinch. For instance, if you have headlight power on K7-30, you can jumper from K7-30 to K8-87 or 87A which should power the headlights independent of the switch and relay circuits. This would test the wiring and bulbs...

 

[timberrrrrr]

Check all your grounds, do you have power at the switch? Cut the circuit in half and work toward the issue. Power at the switch work toward the lights no power work toward the fuse panel.

Thank you for your reply . . .

Just pulled off the dash plate to discover that the plug at the back of the light switch was unscrewed and disconnected. Kinda strange, wondering if somebody disconnected it because there was a drain on the battery somewhere. Will have to wait and find out.

Should have checked this earlier, simple fix, thanks for the help!!!

 

[NDT]

Were the 20 something screws present that hold the dash in place there?

 

[timberrrrrr]

Most were there, about 3 or 4 missing

 

[wheelspinner]

Kiss

 

[aleigh]

Thank you for your reply . . .

Just pulled off the dash plate to discover that the plug at the back of the light switch was unscrewed and disconnected. Kinda strange, wondering if somebody disconnected it because there was a drain on the battery somewhere. Will have to wait and find out.

Should have checked this earlier, simple fix, thanks for the help!!!

My truck had this same problem, after the dash warning light connector half pulled itself out. I think maybe they vibrate out from tension on the harness. Caused a myriad of problems, including the air alarm not working (some would say that was a blessing).

 

[Third From Texas]

Caused a myriad of problems, including the air alarm not working (some would say that was a blessing).

I was wondering if anyone has ever replaced the alarm with a simple red light.

While the various tones might not translate over to visual well, it would still give you a clue something is afoot (or it could work quite well visually).

I've never pulled the buzzer, but now I want to go have a peek at how many leads it has (of course referring to the TM as needed).

 

[aleigh]

For my part I appreciate it. But when I got the truck, there were sticky marks where someone had duct-taped over it at some point, presumably to make it quieter. I can understand that. When I start the truck up the first time I just use the time to do a walk around. Or I just hold my hand over it.

There are really just two noises it makes, the air alarm, and then the troop alarm which I am told is kind of a two-tone noise. I've never heard it, NOS switch but haven't found (or made) a cable, I don't often put people in the back.

Kind of on a tangent my VIC-3 has an alarm input and I've kind of wondered about plumbing it into that for giggles.