ruralandalone Posted July 16, 2022 Share Posted July 16, 2022 I'm making progress on my 86. This week I repaced the fuel level and oil pressure senders, so all of my gauges are working. The last thing I need to fix on my project that is critical is my instrument illumination. Here is the story: When I turn on the illumination via the headlamp switch I do not get any instrument lights. The clock illumination goes out. Not dims, mind. Out. Turn off the headlight switch and it comes back on. I have voltage at the illumination fuse, and the voltage varies when I turn the headlamp switch. So the switch is good. I have power to the clock and cigarette lighter. Since gauges, radio, and lighter work, I have no indication that the grounding is poor. I do not have a working warning buzzer - though it WAS working recently. I have removed the radio, so there cannot be any issue with how I wired the radio. My best guess is that there is a problem with one of the circuits that connects to the dimmer switch. My first thought is to pull the radio/clock illumination relay, and see itfthat helps me narrow down the problem. According to my repair book, the relay is located "under l/h side of I/P, behind kick panel". The wiring diagram shows it wired to the harness at a point very close to the horn relay. I found the horn relay, but I don't see the illumination relay. Or anything that looks like one, nor do I see a socket for one. At this point I'm rather flummoxed. I CAN rewire the illumination directly, but I'd like to identify and fix the existing problem if possible. So I'm looking for suggestions as to what to try. And if anyone knows where the #&$#^$ illumination relay is, please let me know! Link to comment Share on other sites More sharing options...
eaglescout526 Posted July 16, 2022 Share Posted July 16, 2022 I didn’t even know there was an illumination relay. That being said do you have any other lights that don’t come on? Like interior or running lights? Do the indicator lights come on on the cluster? Like turn signal, brake light and high beams? Link to comment Share on other sites More sharing options...
ruralandalone Posted July 16, 2022 Author Share Posted July 16, 2022 Well, the manual SAYS there is one, but as I said, I can't find it. My cab has been pretty much gutted. I don't have much in the way of working interior lights. Turn signals, running lights, headlights (high and low) headlight indicator, brake lights, running lights, glove box light all work. Link to comment Share on other sites More sharing options...
Ωhm Posted July 16, 2022 Share Posted July 16, 2022 88ElectManual shows it (Radio/LCD clock illumination relay), but the 87ElectManual doesn't. MJ_1987_Electrical_Manual_1.pdf Link to comment Share on other sites More sharing options...
eaglescout526 Posted July 16, 2022 Share Posted July 16, 2022 If I recall correctly, the running lights and instrument illumination are all tied into the same circuit. Link to comment Share on other sites More sharing options...
ruralandalone Posted July 16, 2022 Author Share Posted July 16, 2022 Since mine is an '86, it SHOULD have the relay. That would appear to be correct, in that the running lights and illumination are both controlled by the headlight switch. Different circuits, though. Whatever the problem is, it would seem to occur downstream of the instrument fuse.. If there IS no relay, then there must be a wiring short someplace. Anyone have experience with a Automotive Short and Open Finder Circuit Tester? I'm wondering if one would be useful in this situation..... Link to comment Share on other sites More sharing options...
ruralandalone Posted July 17, 2022 Author Share Posted July 17, 2022 ok. No dimmer relay. One less thing to check Link to comment Share on other sites More sharing options...
ruralandalone Posted July 17, 2022 Author Share Posted July 17, 2022 I'm going to have to pull the cluster. Any tips on how to do this? How do I get the speedo cable off? Link to comment Share on other sites More sharing options...
eaglescout526 Posted July 17, 2022 Share Posted July 17, 2022 Oh shoot, must’ve missed you’re first response. So pulling the cluster out is easy. There’s four screws holding the dash bezel in place. Remove them and you’ll need to gingerly finagle the bezel out of its hole. once that’s removed, getting to the cluster will be cake. But to remove the speedo, you might have to either crawl underneath the dash or get the cluster maneuverable to where you can depress the metal retainer holding the speedo cable in. Link to comment Share on other sites More sharing options...
ruralandalone Posted July 17, 2022 Author Share Posted July 17, 2022 By cluster, I mean the whole assembly, including the case, since I have to access the wiring.. I assume you do too. My initial attempts suggest that it is a really tight fit. It almost looks like I have to lower the entire steering column to get it out. I hope not. In other cars I have dealt with there has been enough play, or easy access to, the speedo cable. My initial looks underneath the dash don't even suggest a view of it, let alone anywhere I can get my hand in. Can you describe how is it clipped on? Link to comment Share on other sites More sharing options...
525JoeComanche Posted July 17, 2022 Share Posted July 17, 2022 I find it easiest to remove the speedo cable from the transfer case as well as any retaining clips holding the speedo cable along the length of the underside, and then you can gently pull the cluster out with the speedo still attached and then can remove it easily since the cluster will be out, makes for a much easier time putting it back in too. Link to comment Share on other sites More sharing options...
ruralandalone Posted July 17, 2022 Author Share Posted July 17, 2022 That helps. Thank you. Link to comment Share on other sites More sharing options...
eaglescout526 Posted July 17, 2022 Share Posted July 17, 2022 Shouldn’t have to remove the column at all. Link to comment Share on other sites More sharing options...
ruralandalone Posted July 17, 2022 Author Share Posted July 17, 2022 I rather hope not, as that means the lower instrument panel has to come off.... (: Link to comment Share on other sites More sharing options...
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