StarGeneral

Hello again! back with my next problem to tackle: My speedometer back lighting doesn't work!

Here's the run down on what works and what doesn't on the speedometer PCB:

• Left turn signal light stays on when headlights are turned on, and flashes on and off correctly when left turn signal is activated. Occasionally does not come on when car first starts.
• Right turn signal does not stay on or flash when headlights are activated or right turn signal is activated.
• Hi-beam indicator does not work.
• The two speedometer backlights do not work.

Things I've tried so far:

• Replaced and re-inserted every socket bulb into PCB.
• Checked connectivity between speedometer cluster connector and the prongs on the PCB...no issues here!
• Wiggled socket bulbs in their slots while the headlights were turned on.
• Wiggled speedo cluster connector while headlights were turned on.
• All fuses are brand new as well.

So, I'm thinking the problem is the PCB itself. Somehow electricity isn't flowing through most of the board. I have noticed some wear on it.


For example, the PCB itself is a dull rust color, but the electric pathways are greenish. Some of the pathways appear scratched or spotty (the ones leading to things that do not work) while the left turn signal pathway is relatively intact.


I know my chances of finding another PCB or speedometer are low...so how would i go about repairing this thing...is there anything I can really do? And if I'm wrong about the PCB being the issue, where else should I look?


Thanks for reading!

rocketraider

We're assuming the gas gauge, clock and heater control lamps work?

You can try cleaning the brass contacts in the lamp sockets with some fine sandpaper or other abrasive that will get down in there, but if the circuit board is damaged as you described, that's where I'd start. It's weird to hear of that part being damaged like that. The fiberboard PC's were pretty tough, esp compared to the flimsy Mylar plastic ones used some years.

65-66 B & C body circuit boards are the same and you can find them NOS on ebay every so often, cheap. There is some difference depending if the car has a speed alert speedometer (buzzer terminals), but they both fit the same.

OE part # for your search:

Grp 9.744 p/n 6408910 plate, speedometer, 65-66 5200, 5400, 5600, 5800, 6600, 98 except speed warning

Grp 9.744 p/n 6408902 plate, speedometer, 65-66 speed warning except F85 or Toronado

5200= Jetstar 88, 5400/6600= Jetstar I/Starfire, 5600= Dynamic 88, 5800= Delta 88

There's a few guys on here with these cars who may have a good spare board or speedometer. I doubt you could successfully repair the one in the car.

StarGeneral

Thank you for the suggestions, yes all the lights on the gas gauge work. I will try to sandpaper the contacts on those bulbs first. My speedometer does not have the safety sentinel feature its just a standard one.

One other light that doesn't work is the HMT indicator light....for some reason it just doesn't work. It's a bit weird. Its a gray wire socket that comes right off the harness too, so I don't know where the failure point could possibly be.

rocketraider

SG, I'm starting to wonder if you have a grounding problem. The LH turn indicator staying lit makes me think that- it may be trying to ground thru that park/turn circuit. Conversely the park/turn lamp may be trying to ground thru the dash cluster, which would also cause that symptom.

Have you actually had the speedometer cluster out of the dash? What I'm seeing in the CSM is that the lamps ground thru a pair of buses on the printed circuit, thru the 4 screws that attach the PC to the cluster housing. The ground path then goes from these screws, thru the housing to the 2 screws that hold it in the dash.

Take the thing out and play with it some, cleaning up all the connections. Worst that happens is it still doesn't work; best is that the problem is fixed.

Looking closer, the HMT indicator lamp pigtail should have the gray power wire you've found as well as a black ground wire that attaches to the dash metal somewhere close by. Also make sure it's plugged into the harness a few inches back from the HMT indicator- stick or floor shift cars did not use it so they had a jumper for column shift automatic cars.

Do you have your own 1965 manuals yet? If you're still using the wildaboutcars scans, look in Section 12, Instrument Panel 52 thru 86 series. Fig 12-13 shows the HMT indicator jumper as well as the instrument panel wiring. Fig 12-5 shows the speedometer cluster PC.

StarGeneral

I will remove the speedometer completely next time I get a chance and disassemble and reassemble it, and then I will post back on my progress.

I did tighten those grounding screws a couple days back and had some weird results with the speedo....now the right turn signal indicator is the one that works. I did some experiments trying different sockets and bulbs and decided that the problem had nothing to do with the bulbs or sockets themselves. It probably is a grounding issue, but Ill clean everything just to be sure.

StarGeneral

got the unit out today...seems to have suffered extensive water damage. The board is warped, some of the pathways seem scratched. I cleaned the contacts on each bulb socket and bent the prongs forward so hopefully the contact is better...will report soon on result.

StarGeneral

Ok, so now that I've had a chance to pull the unit, clean it and subject it to some tests, I will post my findings here:

1. Right after re-installing the unit, only the right turn signal indicator flashed, and with headlights on, the indicator stayed solidly lit unless the right turn signal was activated, then it flashed on and off as it should.

2. I swapped the socket and bulb from the rightturn signal with that of the left. After that, the left turn signal indicator blinked properly with headlights off, and stayed solidly on with the headlights on, unless the left turn signal was activated in which case it flashed properly.

3. I then removed both indicator bulbs and sockets and inspected them closely. I tried to identify what was different about the two that would cause one to work and not the other...but I could not find anything different between them.

4. After that, I swapped sockets and bulbs until I got BOTH turn signals to activate properly...However, with the headlights turned ON, the opposite indicator light flashes instead of the one that is actually supposed to.

4a. Swapping bulbs and sockets also made the speedometer back-lighting come on when the headlights are on....but when either turn signal is activated, both back lights flash on and off in time with the signal.

CONCLUSION:

What i think is going on is somehow the electrical pathways on the circuit board are getting crossed when the headlights are activated. I do not know much about the wiring circuit in relation to the headlights, but thats what it seems like is happening.

So now I turn to you guys, do you think the culprit is the PCB? the headlight switch? or maybe something else entirely?

A member of this forum has offered to sell me a speedometer unit so replacing it is always an option. We have already established that the entire unit has suffered water damage...but you guys know more than I do about electrical gremlins so I wanted to see if you had any suggestions.

rocketraider

SG, can you tell if that car has ever gone thru a flood? I cannot fathom water damage behind the dash unless the car was flooded or it had a rotted out lower windshield channel.

Since the socket and bulb did the same thing when swapped to the other side, did you check the contact strips on the bulb to make sure they're not crossing inside the socket?

Shame you're across the country. We'd figure this craziness out.

Right now I'm thinking the circuit board is the problem. Rob, if you're following this, look at the pics Eric (jensenracing) posted of the speedometer circuit board in that 66 98 he's parting, and see if you think that connector plug pin can be salvaged.

StarGeneral

I dont think it has been through a flood...the speedometer unit has a level of rust on its case not consistent with the rest of the car, so I think it may not even be from that car originally. I did check the contact strips and they are not crossing inside the sockets...so its really weird. At least at this point i have my turn signals functioning properly when the headlights are off.

Its awfully annoying to use them at night though and have my speedometer lighting flash on and off every time I make a turn XD

About the connector pin, it can probably be replaced as they seem to simply be stuck in the circuit board from the other side. I could probably just take one off of mine and stick it in the hole after removing the damaged one. But I found someone who is willing to sell me a whole new speedo for $25 + shipping

Unless of course he just wants to sell the PCB, in which case that'd probably be cheaper for me to buy.


Here's some pictures of my unit:

Scratching on pathways...

More scratching on pathways....

You can see how warped it is here...

rocketraider

Here's a fix for broken CB connector pins courtesy of texxas8902 at 73-77olds.com ! I thought it ingenious- simple and elegant! He used very small machine screws and noted that the screw will cut its own threads into the I.D. of the connector pin.

StarGeneral

Even though im planning to get a new board, I noticed now that if I take the right turn signal socket and bulb while everything else is on, all of the lights in the speedometer go out. Removal of any other bulb does not cause this. What could this mean?

I also switched sockets and bulbs again today because I put red leds in for my lighting and now I've got all sorts of crazy problems going on. I get different results every time I plug in the bulbs and sockets a different way. It seems almost random.