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Dash light/headlight switch issue

MPLSBlazer

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I'm in the process of cleaning up cab wiring on my '84 jimmy (previous owner hacked it up fairly extensively) and I've hit a problem that I don't understand - hopefully some folks with more experience can help!

The Problem:
My dash lights don't come on when the headlights are on (or any other time)

What I've tried:
I was able to find a shop manual at the local library that has full wiring diagrams for the jimmy. With the manual, I've identified the wire in the plug going into the back of the dash that should be the dash light power (circuit 8 - gray wire for those of you following along at home). I traced that wire back to the fuse box and replaced the fuse but that didn't fix the issue (the old one didn't look blown, but better safe than sorry). At this point, I popped the fuse and tested with the headlights (which functional properly) switched on - no power. So I went back to the manual and started tracing back from the fuse box to the headlight switch. I've attached a picture of the manual showing the headlight switch, but my electrical skills aren't exactly expert level so I'm not positive what I'm looking at - I believe the dark green wire (circuit 44) goes to the other side of the fuse from the grey wire that runs the dash lights. I tested by jumping the red wire (unswitched power) and the dark green wire, which turned on the dash lights. Success!

The questions:
The above process seems to tell me that the switch is the problem - am I interpreting correctly? And if so, I'm considering replacing the unnecessarily complex headlight switch setup with a simple toggle switch; how should that be wired? Just red wire on one side and the rest on the other? Or should I just try to find a replacement stock-style switch mechanism?

Thanks in advance for your help!

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diesel4me

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There is a fuse for the instrument panel lamps marked "LPS" in the fuse box,I assume that is the fuse you mentioned you replaced..(I dont see any gray wire in your wiring diagram,just the dark green one..)

I'm not that muxh of a whiz at wiring issues but from what you described,if you can jump constant power to the plug on the switch that powers the dash lights (which would be #1 and #2 on the switch near the rehostat ),then it could be the switch is not making contact inside to connect those 2 together and light the dash bulbs up...

It might be just the rehostat coil has failed or gotten all corroded,that controls the dash cluster lamps brightness...my '82 I have to rotate the switch sometimes to get the dash lamps to come on..(I do not drive at night hardly at all,so the switch probably corrodes from not being used often enough)..

I would just get another headlamp switch,either "good used" or new,seeing yours is about 33 years old,it may well be dying --cheap insurance,you don't want your headlamps to shut off some night on a dark road with no street lights!....(I had that happen more than once and was lucky I didn't crash)..

If you were to put a toggle switch in its place,you'll need a heavy duty one,50 amps would not be overkill,unless you add a relay to take the load off the switch..
--remember the headlights are not fused,they have a circuit breaker that clicks off if there was a dead short,and turns back on after it cools off--you need either a circuit breaker or fuse to protect the wiring,otherwise it'll just burn up if there was ever a short..a fuse will just pop and leave you with NO lights,a breaker will "flash" on and off and maybe give enough light to pull over before you hit something..

Its much easier to put another OEM switch in and know its rigged the way they intended it to be..
 

dyeager535

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Unfortunately you are pretty much stuck with the stock mechanism, unless you were to convert over to relays for the headlights, and were willing to eliminate dimming in the cluster. It's not overly complex, it's actually less complex than the alternative, which is a heavy duty relay (or two, with integral self-resetting circuit breakers), separate dimmer assembly, key buzzer, and wiring to all of that. The stock switch seems complex, and it is, but it's a far more compact (and cheap) setup than the alternative.

I've seen some pretty poor aftermarket headlight switches, if you have to get one, try and get one with a warranty. I've seen the rheostat portion fall apart in short order.

I suppose if your only problem is the cluster lights, and dimming isn't something you care about, you could power that circuit separately, but you just fixed someone else's wiring job, now you know why you don't deviate from factory unless you have a very specific reason, and know what you are doing. :)
 
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