Clock wiring info? Only works with headlights on, resets to 10:00.

[memsiej]

Clock is acting up. It only works when my headlights are on, and then resets at 10:00 every time.

On ol' Tom's page I can find a diagram telling me what colors the 5 wires are at the connector for the clock, but not what each wire does. Anyone know?

Also, someone else suggested the ignition switch might be a culprit. I just replaced mine a few months ago, but more so I am curious how the ignition switch it linked to the clock. I can't see any connection on any wiring diagrams.

Thanks

[tgreese]

A clock is supposed to be powered all the time. A modern clock would include a super cap or battery, to maintain its memory - just like your computer. Maybe the clock is so old that the super cap supporting the ROM is worn out. Seems likely super caps would be around in 1984. Or it's powered by the Jeep battery constantly. Seems like a less desirable arrangement, since the clock would lose memory if you replaced the car battery.

First thing I'd do is look at where each wire goes. Post it up, and test each wire with your multimeter. If the TSM does not have a section about the clock, then there was probably a supplement that the dealership would have.

[memsiej]

My findings for the car side of the connector. Plenty of power at everything with headlights on, but less so with headlights off. I'm betting the white or orange wires are the 'always hot' wires, and the other is the memory. But I don't know why they would only work with headlights.

[tgreese]

I would trace through the wiring to see if the connection to the headlight circuit is intentional.

What does the clock do normally? Is the display lit with the key off? I would expect black to be ground and red to be power. Did you look in the TSM?

https://en.wikipedia.org/wiki/Supercapacitor

[memsiej]

It is intentional. It's what allows the clock to illuminate brighter when the headlights are on, and lets that illumination be controlled by the turning of the headlight switch.
Normally, I think the clock should be always on and retaining it's time, getting brighter when the headlights are on. That being said, I'm not 100% sure and cannot check.

WIth all the wires checking out and doing what they're supposed to do, I'm leaning towards broken clock.

[tgreese]

My educated guess is that whatever the backup power source is, its condition is so poor that its voltage drops quickly. The clock loses memory soon after as the storage goes completely flat. This causes both the shut down without the lights, and reset when the lights come on. A clear objective of this circuit would be to prevent draining the car battery via the red wire, if the Jeep is parked and idle for a looong time. Also possible that this minimizes the memory drain when the internal power source is low, to try and keep the memory working when the Jeep is idle for a looong time.

If the internal battery or cap is weak, the memory storage goes away quickly. This pretty much matches with the symptoms you report.

What I would do - maybe not the right approach for you. I would open the clock case and I'd probably find a super cap or battery. Whatever I found, I would replace. Likely you will have to solder in the new part.

[memsiej]

I may crack it open and poke around. No reason not to! I'll report back.

I have a new unrelated question and you're pretty well informed. Gonna PM you to not clog up this thread.

[tgreese]

Hi - I looked quickly at your PM. I suggest you post a new thread with your question. Seems suitable for a technical post, and then everyone can benefit from the combined wisdom. More posts are a good thing. IMO PMs are for personal message like buying/selling, meet-ups and such.

[Curly]

Hi, I found this info on an older thread on here. The purpose of 2 hots is to keep the clock time accurate when the key is off. Post 3 from the thread below,


black =Ground
Blue =Hot with ignition on only
Red = Hot all the time
Yellow & Orange = Is what I call variable, able to dim and brighten like your dash lights. (Splice the yellow and orange wires together)

http://www.ifsja.org/forums/vb/showthread.php?t=31964

[memsiej]

Red is getting it's constant power, as it should, but it's performing its function at the clock, which is leading me to believe it's a problem with the clock.