Need help with dash lights

[Rich69shortfleet]

I was in the process of putting LED bulbs in my instrument cluster and in the end found out I have no power to the instrument lights at all. Before I started this process I had all panel lights with no problems. I have the cluster out and the circuit sheet is fine. All the instruments work fine. The dash lights in the heater controls is also out.

The headlight switch appears to be okay. Through my testing I found that when the headlight switch is off the PNL LTS fuse is not powered. When the headlight switch is on the PNL LTS fuse is powered. However, when trying a test light between the grey No. 8 wire in the cluster feed plug and ground I get nothing when the headlight switch is on. The ground to the harness is fine and I get continuity between the body and the ground wire in the cluster harness plug.

HOWEVER, the part that has me baffled is this. When I try to check continuity from the PNL LTS fuse to the No. 8/grey wire terminal on the cluster plug I get nothing whether the headlight switch is on or off. Okay, this seems to point to the grey wire somewhere between the fuse panel and the cluster plug. HOWEVER, I do have continuity between the No. 8/grey wire terminal in the cluster plug and ground. Okay, so the grey wire is grounding somewhere, but if so, why isn't the fuse blowing?

There has to be something else going on here that I'm not getting. The wiring is all very solid and has never caused any issues. All I was doing was changing a few bulbs and now an entire wiring circuit is fubar? I'm missing something obvious I think.

[LockDoc]

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This ground clip that grounds the cluster didn't come loose did it?

LockDoc

[Rich69shortfleet]

Originally Posted by LockDoc

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This ground clip that grounds the cluster didn't come loose did it?

LockDoc

Nope, it is still there. And I get continuity between the piece it is clipped to and the ground wire in the cluster plug.

[dmjlambert]

Does it work when you put the regular plain light bulbs back in? It is best to troubleshoot with regular incandescent lights.

[Rich69shortfleet]

Originally Posted by dmjlambert

Does it work when you put the regular plain light bulbs back in? It is best to troubleshoot with regular incandescent lights.

No. I have no power to the grey wire at the cluster plug now. No idea why. I haven't touched the wiring.

[dmjlambert]

Do you have a gauge cluster or warning light cluster?

When testing continuity between ground and the point on the printed circuit were the grey wire connects, are you using an alligator clip? I ask because I did that and realized when I got a short it was because bottom jaw of the alligator clip was clamped on the metal case of the cluster and top jaw on the printed circuit trace, which are normally kept separate with a thin sheet of plastic. So I started smoking my test wire. So, proceed with care.

You say you are getting continuity between the No. 8/grey wire terminal in the cluster plug and ground, I think that may be normal with the lights off. I can't really mix continuity tests and voltage tests without confusing myself, so I usually stick with one or the other. Testing for voltage present or not present relative to ground will check the circuit under load, which is usually better than continuity test that puts very little load on the wire.

How is the headlight switch turned when you are checking for voltage on the grey wire? It is a dimmer, so turn it all the way up, which is counter-clockwise.

[dmjlambert]

Another thought, rusty connections are normal in these old trucks, so remove that fuse and clean up the terminals that hold the fuse, clean up the fuse, and re-insert it.

Do you have one of those handheld test probes with the wire and clip that you connect to ground, and a tip that you go poking around with to test for voltage? If so, be careful with that around the printed circuit because it is easy to poke right through it.

[Rich69shortfleet]

The cluster is completely out of the truck. I am testing at the grey wire terminal on the cluster plug only. I am testing with a lighted probe. I've tried testing with the headlight switch turned to any number of positions. The dome light comes on at the extreme position so there is power in the switch. As I said before, I get power across the panel lights fuse when the headlight switch is on, but I get no juice at the grey wire in the cluster plug. I have a new headlight switch I will try, but I don't know how it could be the switch if the panel lights circuit is energized at the fuse panel when the switch is on.

I followed the test procedures posted by VetteVet in this thread:
http://67-72chevytrucks.com/vboard/s...ash+lights+out

[dmjlambert]

This is the circuit.

If your tester is showing voltage at the fuse, my top suspect would be bad fuse (I've seen weird stuff like that before, fuse tests good but is actually bad under any load) or poor connection of the fuse in the fuse holder. It is possible to be somewhere along the grey wire, and if so the most likely place would be where the wire connects to the terminal inside the fuse panel or inside the connector. You can poke through the grey insulation with the tester to check voltage in the wire.

[Rich69shortfleet]

Originally Posted by dmjlambert

This is the circuit.
Attachment 1769847
If your tester is showing voltage at the fuse, my top suspect would be bad fuse (I've seen weird stuff like that before, fuse tests good but is actually bad under any load) or poor connection of the fuse in the fuse holder. It is possible to be somewhere along the grey wire, and if so the most likely place would be where the wire connects to the terminal inside the fuse panel or inside the connector. You can poke through the grey insulation with the tester to check voltage in the wire.

I'll try to follow the grey wire out of the fuse panel and see where it may have power. I'll pull the fuse panel down if need be. I'll also try another fuse.

Do you know which end of the fuse the power come out of to go to the cluster? I'd like to try a jumper wire but I will want it to go through the fuse so I'd need to connect it onto the outbound side of the fuse, otherwise my jumper will be bypassing the fuse and I don't want to burn down my harness or dash panel in the process in the event there is something else going on.

[dmjlambert]

Map of panel http://67-72chevytrucks.com/vboard/s...d.php?t=741245

[dmjlambert]

See if you are getting power at that terminal for other accessory dimmed lights. If so, just connect there.

[Rich69shortfleet]

I have a good list of things to try. Weather turned crappy so it will be a while before I care to go outside to test things again. I'll post back when I know more. Thanks for the fuse panel display, that helps a lot.

[stsalvage]

You try the light switch Its the one thing that can do it.But i've seen the horn relay do the same thing

[Rich69shortfleet]

Weather is still crummy (cold) but I was able to eliminate the headlight switch as the problem. I bought a new one and this did not solve the problem. It too energized the dash lights circuit but there is no power at the grey wire in the cluster plug.

One odd thing was observed which may tell me something, but I don't know what yet. With either of the headlight switches in place (old or new) I found that there is power across the PNL LTS fuse. HOWEVER, the power across the fuse is barely enough to light my test light. Regardless of where the headlight knob is turned the illumination of the test light is the same dim output. I CAN turn off the power across the fuse with the headlight switch but once the test light lights I cannot increase the brightness of the test light. So perhaps this tells me that the power from the green wire from the switch which energizes the grey wire circuit is weak.

I guess my next step is to pull the fuse block down and see if there are any weak points in where the green wire from the switch comes in and where the grey wire goes out.

As a side note and observation, the new BWD headlight switch at the first stop turns on the headlights and running lights and at the second stop (pulled out fully) turns on only the running lights unlike the original which turns on the running lights at the first stop and both the headlights and running lights at the second stop. WTH? This switch is going back, I'll continue to use the original.

[Rich69shortfleet]

Since it has been Winter here all over again I haven't made any progress. Next few days should be better, we'll see. I've had an idea of where this could be failing so we will see if I'm a genius or if I'm just chasing my tail some more.

Still can't believe what a piece of crap that replacement headlight switch was. At least I was able to determine the switch was not the problem. O'Reilly took it back without any issue.

[Rich69shortfleet]

Weather finally returned to a semblance of sanity so I've had some chances to dig further into the issue. I checked the light at the lighter and the heater controls and found no issues. So, since the dash is all torn out and I have more ready access I pulled the fuse panel off the firewall. When I unbolted the harnesses in the engine compartment I did not find any issues at least not any that looked obvious.

When I pulled the fuse panel down I checked the continuity along the green wire at the headlight switch to the panel; all good. I also checked the continuity along the grey wire from the fuse panel to the cluster bulkhead; all good. Okay, if the wiring is okay, that pretty much leaves the fuse panel. The fuse clips looked clean but I scraped them anyway and still got a weak signal across the fuse clips. I then looked at where the green wire attaches to the fuse panel and it looked solid. The grey wire clips to the other end of the fuse so I pulled it loose. It looked 50 years old but not corroded but I cleaned it off and reseated the grey wire clip and lo and behold I was now getting a strong clear signal across the fuse.

So, I'm still not entirely sure where the restriction was but I suspect it was where the grey wire clipped onto the back side of the fuse panel and by removing it and reseating it I got a better connection. This would also explain why the problem persisted until I pulled the fuse panel down.

I still have to put it all back together but I did plug in the cluster and installed the dash lights with LED bulbs (which is why I started in on this odyssey in the first place) and they happen to look fantastic, very bright. They don't dim with the headlight switch, they are either on or off, but that's just fine with me. These trucks' dashlights have always been so dim even at the brightest setting I like the opportunity to brighten them up a little bit more. Given how the LED bulbs are built and how the fiber optic cable feeds light to the column shift indicator I don't know if the LEDs will properly illuminate the shift indicator but we'll see when I get it all together. I'll also need to buy a few more different kinds of bulbs to also LED the turnsignal indicators. I might as well do the glovebox lamp as well.

[Rich69shortfleet]

It would appear no one cares anymore about this thread since all the posts are from myself, but I got the dash lights all working and powered by LEDs. Here is a photo of the dash lit with LED bulbs.

[bill3rail]

I care! I usually follow threads to see the outcome.
I thought you would have a ground issue like I did.

I ran a second ground and dash issues left. You can't have too many grounds...

Bill

[LockDoc]

Originally Posted by Rich69shortfleet

It would appear no one cares anymore about this thread since all the posts are from myself, but I got the dash lights all working and powered by LEDs. Here is a photo of the dash lit with LED bulbs.

Somebody must care, it has 530 views. Many people don't have any more to input but follow along to see the outcome of the problem. I think it's great that you posted the actual fix, lots of members don't do that. Now the fix will be here for others that might have the same problem down the road....

Kudos.

LockDoc

[jamie72]

so what leds did you use?

[Rich69shortfleet]

Originally Posted by jamie72

so what leds did you use?

Simple ones sold by jtechnowcom on ebay. I think a set of 10 cost less than $7. I didn't want to spend too much in the event they wouldn't do the trick. I might upgrade to better quality LEDs in the future, but for now they are really doing the job.

These are the ones I used: https://www.ebay.com/itm/10x-T10-8-S...72.m2749.l2649

And FYI, if all you want to do is to upgrade the instrument illumination (194), a set of 4 would do the trick. With a set of 8 (you only need 7) you can do the instrument illumination, high beam indicator and the brake and temp warning lights. The turn signals (1895), heater controls (1445) and glove box (1445) bulbs are a different design and you have to get different bulbs if you want to do those too.

[Rich69shortfleet]

A little follow up. I was bugged by the fact that the amount of light getting to the transmission selector via the fiber optic cable was almost nonexistent with the LEDs. I even tried a different LED that puts light out to the sides as well and it made no difference. So, I knew it would bug me more and more over time so I put a normal bulb in the socket with the fiber optic cable. Then the lighting was uneven and more yellow than where the LEDs were. I then put one of those little green rubber bulb covers on that bulb and the color matches and the light output is pretty even across the cluster AND I have my transmission gear selector properly illuminated again. Win-win. And I've still lightened the electrical load on the dash lighting system by probably 90% or more. I will also be adding LEDs to the turnsignals, glovebox and heater controls lighting as soon as those bulbs arrive in the mail tomorrow.

[Rich69shortfleet]

Another follow up. Can't put an LED in the glovebox since that socket puts the ground to the bottom of the bulb and the hot to the side (the opposite of other bulb sockets). LEDs require a specific polarity so one won't work in that particular socket.

[Rich69shortfleet]

Last week I drove the truck at night. I was disappointed in the illumination of the lower gauges, they are all pretty dim while the upper gauges are nice and bright. Also, with the white LEDs the gauge faces are all white with the reflected light into the housing not picking up the green tinge like occurs with incandescent bulbs. This results in green illumination in the captions on the lens face with white on the gauge faces. So, I got some green LEDs which also have side firing diodes to hopefully illuminate the lower gauges better.

The result is much better illumination of the lower gauges and everything appears green (which I like and prefer). The new LEDs are much brighter than the incandescent I have in the spot that feeds the shift indicator which then made the lighting more uneven in both color and brightness so I put an LED in that location as well. This lessens the illumination of the shift indicator, but still lights it so I'm calling it good.

The gauges now match the color and brightness I've gotten in the heater controls so everything goes together well now. More pleased.

The leftover white LEDs will get recycled into use on other vehicles I have. I've already completely LED-ized my daily driver and am working on doing so on the wife's car. Her car has an incredible number of interior illumination bulbs.