OBC buttons (do not light up)

Post here for mechanical and engine topics such as fuel issues, transmission problems, rough idle, exhaust, electrical issues, etc

Moderators: GRNSHRK, ron, bfons

Post Reply
KINGJOHN808
Posts: 127
Joined: Sat Feb 16, 2019 2:27 am
Location: Ewa Kai

OBC buttons (do not light up)

Post by KINGJOHN808 »

Aloha!

Couldn’t find the answer I needed so I thought I would start a new topic. Can’t remember the last time I saw the buttons on my OBC light up. I know it worked back in the 80’s but do not believe it has worked in the last few years.

I changed the fuse to the OBC computer because the unit wasn’t working at all. I assumed that once the fuse was replaced that it would take care of the “All” the OBC issues. Good news, the OBC works (temp, time, etc). What still doesn’t work is the bulb/button illumination.

I changed the bulb several times with known working units. I know they work because I applied 12v directly to the replacement bulbs and they all illuminate. When I pull the light switch, all other lights work (dash, cigarette lighter bulb, a/c slider knobs etc).

I checked the housing where the light attaches on the back of the OBC, and have 12v (on all three post, this is visible when you remove the cover from the OBC. Not understanding why I have power, but no light.

I’m tempted to buy another used OBC, as I am completely stumped as to why it still doesn’t work. Any ideas are greatly appreciated. Not sure if I’m missing a ground or if there is something not programmed or reset in the OBC.

This is a 1984, 633CSi. Automatic, US version. Gonna try to add pics pointing out what I’ve found and changed so far.

Mahalo’z
Attachments
6045CBFB-61C5-4411-B53C-AC3FE9AC3DDE.jpeg
6045CBFB-61C5-4411-B53C-AC3FE9AC3DDE.jpeg (1.78 MiB) Viewed 861 times
DE44B8A2-E87F-4E7B-AA7D-ABFE3E2F80D6.jpeg
DE44B8A2-E87F-4E7B-AA7D-ABFE3E2F80D6.jpeg (1.82 MiB) Viewed 861 times
AE25E7CB-D0CA-4C9A-A3C8-147D1E1174E6.jpeg
AE25E7CB-D0CA-4C9A-A3C8-147D1E1174E6.jpeg (1.77 MiB) Viewed 861 times
Ewa Kai, Hawai’i
1984 633CSi
1983 633CSi (wreckers)

“Aloha and have a great day!”
KINGJOHN808
Posts: 127
Joined: Sat Feb 16, 2019 2:27 am
Location: Ewa Kai

Re: OBC buttons (do not light up)

Post by KINGJOHN808 »

Well….

I don’t think it’s the OBC display panel. Had a spare out in the parts box. Did the exact same thing as the previous unit. Switched out the OBC computer under the dash…still no button lights. Display works though, along with all the LEDS but no buttons.

Question…I understand that the buttons will only light up when you activate the light switch. I get power to the light on the OBC (11.7v) give or take, however when I turn the dimmer knob, the power to the light (on the OBC) doesn’t change.

I’m starting to think that the problem is else wear meaning originating from the instrument cluster as the switch connects to the cluster, then to the OBC. Since I have to take out the cluster to repair the “D,P,3” light bulbs and one of the dash lights, will take a look at the wiring to and from the cluster.

Hopefully, can locate the issue as it seems like a common occurrence or so I’m led to believe.

Mahalo’z.
Ewa Kai, Hawai’i
1984 633CSi
1983 633CSi (wreckers)

“Aloha and have a great day!”
emac
Posts: 178
Joined: Thu Feb 06, 2020 2:57 am
Location: SC

Re: OBC buttons (do not light up)

Post by emac »

do you have 12v at the terminal where the bulb plugs into the OBC?
User avatar
RossDinan6
Posts: 295
Joined: Mon Jan 29, 2007 2:35 am
Location: SW FL, USA

Re: OBC buttons (do not light up)

Post by RossDinan6 »

Looking at my ETM (84), the headlight dimmer does not dim the OBC. It looks to be internally controlled in the panel. I have not worked on this system, yet, so the following may be useless.

The headlight switch supplies 12v + to the cluster, illuminates the lights and grounds through the dimmer. It also feeds the OBC which then feeds the OBC panel. The ETM has "58k Solid State Brightness input 31G" in parallel with the lamp. There is not enough info to tell for sure how it operates. Based on the solid state note and the chips in the pictures I suspect that it may dim with a PWM signal that would not read on a normal multi meter.

I suspect your OBC panel.
Ross
'84 633 Dinan turbo
KINGJOHN808
Posts: 127
Joined: Sat Feb 16, 2019 2:27 am
Location: Ewa Kai

Re: OBC buttons (do not light up)

Post by KINGJOHN808 »

RossDinan6 wrote: Thu Mar 31, 2022 9:46 pm Looking at my ETM (84), the headlight dimmer does not dim the OBC. It looks to be internally controlled in the panel. I have not worked on this system, yet, so the following may be useless.

The headlight switch supplies 12v + to the cluster, illuminates the lights and grounds through the dimmer. It also feeds the OBC which then feeds the OBC panel. The ETM has "58k Solid State Brightness input 31G" in parallel with the lamp. There is not enough info to tell for sure how it operates. Based on the solid state note and the chips in the pictures I suspect that it may dim with a PWM signal that would not read on a normal multi meter.

I suspect your OBC panel.
That’s what I suspected. I replaced both the OBC and the display unit but came up with the same results. I’m over trying to get it working “lighting up” the buttons. The display works fine to include time and temp. Will just inset a light into the housing and power off another signal from a light controlled by the dimmer.

Stay tuned. 🤣
Ewa Kai, Hawai’i
1984 633CSi
1983 633CSi (wreckers)

“Aloha and have a great day!”
Post Reply