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Retrofitting an idiot light housing

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Retrofitting an idiot light housing

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Old 01-25-2018, 06:01 PM
  #1  
HUH? WHAT?
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Default Retrofitting an idiot light housing

Here's my version of how to swap the "internals" of a full gauge cluster over to the idiot light body (housing).

So here's what happened that led me to do the retrofit.

I got my 88 Comanche little over a year ago and one of the features I didn't liked about it was the fact it had the idiot (3/4 gauge) light cluster. Add insult to the injury; it had the column shift, so it had the PRDNL indicator on the cluster.

I knew I had to get rid of it because when operating the Jeep, I liked to know the exact operating values of the various components to make sure they are within safe parameters. With the 3/4 cluster, it's impossible for me to know. The lights would just turn on when something goes wrong, as like if I'm an idiot.

How do you know if the engine is starting to overheat? No you won't know until it overheated. How am I supposed to stop the Jeep in time if I don't know when it's about to overheat? Stuff like that made me dislike 3/4 gauges.

So I looked around and was able to procure a full gauge cluster from an esteemed member (username intentionally withdrawn to protect him from backlash and embarrassment) here on the forum. I paid and bought the cluster from one of his part-outs (89 XJ with 4.0L). Naturally I was excited when the box showed up at my doorstep.

Except... this happened.

Attachment 400856


The member was like "It broke? Oh well, you can fix it".

Naturally I didn't feel like fixing it (I thought about using a soldering iron to melt the plastic together to repair the damage (I have successfully repaired plastics this way in the past)). So I decided to put it on the back burner for now.

Fast forward a year later.

I got fed up with driving with the 3/4 gauges. The oil pressure light kept lighting up every time I went over a bump. **** that ****.

I decided to go ahead with the swap. NOW, I could have done this earlier but there's a perfectly good reason why I kept delaying it...

I always planned on doing the 5 speed swap on the MJ, I figured I would just wait until I actually do the swap and then I ll change out the clusters (remember the PRNDL indicator).

Then I was thinking. Maybe I should just swap the housings with the internals from the full gauge cluster after the 5 speed swap.

Fast forward a year later. I still haven't done the 5 speed swap yet, and I was itching to do a project for the MJ so I decided to go ahead & do it just to kill time. I did a bunch of googling and I saw that most people said both housings were compatible, so I thought I would have an easy time doing it.

BOY they must have obviously assumed that because they obviously have never done the swap themselves.

Attachment 400855

Attachment 400857

The HOUSINGS are NOT the SAME. In fact they are so much different from each other.

Geez. When the things you read on the internet that aren't a proven fact...

So let me back up a bit. I took the cluster out of the MJ, had to unhook the cable for the PRNDL indicator from the steering column. Brought it out to the bench next to the full cluster so I can compare them both

Attachment 400858


The printed circuit papers are completely different. So I flipped them over and removed the plexiglass, and the bezels so to expose the actual gauges themselves. The idiot lights are just translucent panels with pictures on it, basically nothing under it except for light bulbs.

Attachment 400860

Attachment 400859

Attachment 400862

Attachment 400861


The gauges on other hand were hardwired to the printed circuit papers via screws. (There's no holes for screws on 3/4 housing.

The 3/4 housings had long tubes that rises out against to the panels so to project the light toward a single icon.

The gauges sat down on raised bumps to support it.

Attachment 400866

Attachment 400864

Attachment 400865


So after some thinking, I decided I ll cut the tubes down and use standoff's/ spacers to hold the gauges at same height on the other housing.

I also laid down the full printed circuit paper on the back of the 3/4 housing so to see where the holes were located, and marked them. I also saw that 3 locations for the light bulb sockets were slightly off too.

Attachment 400867

Attachment 400869

Drilled all the holes with a 3/16 bit.

I had to go out and buy a Dremel for this project. So I used it to cut the long tubes down to less than .740 (the original height of the base where the gauges sat on on the other body).
I also had to trim one of the fins on the 3/4 housing. The speedo had a trip reset button and when you press on it to reset it, naturally the gauge would move backwards slightly. On the full cluster housing, it had a fin that was tall enough to make sure it doesn't move. So I had to measure that height and make sure when I cut the fin down, it was at same height.

Attachment 400863

Attachment 400870

I highlighted the area with a black marker so it's easier for you to see where I cut.


As for the tach, I had to sand the base down to .350 tall so the tach can sit on the correct height.

Attachment 400873

I bought some 1/4x1" nylon spacers and cut them all down to .740" I only needed 11 of them. I also got some 3/8x1" nylon spacers & cut two down to .350 and two of .150.

Attachment 400871

I dry fit all the gauges on the 3/4 housing with the spacers to make sure they all fit good. And they did. So I took everything off.

Attachment 400868

Attachment 400872

I also reset the mileage on the new speedometer to match my original cluster.

Attachment 400875


I also cut out a slot on the bottom of the tach so the PRNDL indicator will show.

I read somewhere that painting the insides white or silvery color would help the light bulbs reflect off & make the backlighting somewhat brighter. So I thought that was a good idea. Unfortunately only white I had was ceramic engine paint so I just said **** it and used it. I think it turned out pretty well.

Attachment 400874


I assembled everything back on, plugged in the light sockets (I bought some led lights upgrade kit from One Way Lighting, thanks Jason). It was a good time to install it. I used the black bezel from the MJ 3/4 cluster with the black gauge faces off the XJ cluster along with the plexiglass cause it had the hole for the trip reset button. I think it came out nicely.

Attachment 400878

I reinstalled it back on the jeep. I like it. A lot

This swap gave me more than just one upgrade... I now have a functional cluster, a trip meter, a gas gauge with yellow light that goes on when it's low on fuel ( I don't know why the 3/4 cluster doesn't even have that considering they are called "idiot lights" haha.

Attachment 400876

Attachment 400879

Attachment 400877


So that's that.
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Old 01-27-2018, 02:17 PM
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Awesome. I'm really this retrofit isn't more common.
Honestly, who would want a 3.5" fuel indicator with no tachometer?
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