Project: Slippery Slope – a ’91 MJ runner

[eaglescout526]

What job does each of those relays have inside?

[Gjeep]

These are only present HO years in this location -- 2 are factory (dash illumination & horn) and 2 are from me (starter kill & dome light supervision when doors unlocked). 4 relays fit there perfectly without hitting metal support structure of main dash. 

[eaglescout526]

Neat!! Didn’t know that. 

[NickyV]

Is the starter kill a security feature? I've been thinking about how to add an extra layer of protection to my MJ besides Ye Olde Club.

[Gjeep]

Not from the factory. Its a me add on via an old Viper brand alarm. Jeep did have a problematic security system in 91/92 for the higher end XJs but the MJ never got it. And majority of XJ owners I understand uninstalled it because it was leaving them stranded. I wanted all the lock/unlock features of a ‘modern’ truck since I took the time to add power windows and door locks. There are a couple ways can wire a kill switch solo though. 

[jodawill]

On 12/23/2024 at 5:18 AM, Gjeep said:

Key Parts parts installed – new set of repop taillights and linkage bumper set. As always, I try to avoid installing with rivets, so a stainless steel truss screw was used instead.

 

 

 

 

This MJ will also get a power actuated tailgate lock similar to my other MJ tied into the power door lock wiring. The wiring isn’t as pretty as in my other MJ as I am constantly reminding myself to keep the focus of this build as a runner – an MJ to be used.

 

 

Full window upgrade installed and working. 97+ XJ door handles were installed as I like the look of them over the original. New door to body bumpers and various plugs installed, in addition to fresh door lock cylinders to replace the brittle factory installs.

 

 

And finally, the floorboard was POR15'd for a long and rust free life.

 

 

Where did you get those tailgate bumpers? I see some on eBay for $40. I'm not sure what the quality is like.

 

Edit: I found a post about the Key Parts one on eBay. It sounds like that's the closest to the OEM parts, so I ordered them. I'm glad I saw your post! I didn't know you could buy those. Mine are in rough shape. Thanks!

[Gjeep]

I got to cutting on an XJ roof rack for the MJ 80’s inspired light bar. Lots still to do around drilling another mounting hole on each rail, strategy around the holes needed for wiring and overall clean-up/ paint. Here she sits – not attached to the roof at all hence the gap between the roof and roof rack rail. I’m feeling good about this light bar, just not looking forward to drilling the hole at an angled surface…

 

 

 

Also finally got around to bleeding the brakes after all the new parts were installed months back. Had a heck of a time with the front passenger line not bleeding/ getting any fluid. Zip. Nada. Never had something like that happen before so I took to Googling — the answer and fix — stomp on the brake pedal repeatedly. It resets the proportion valve to all open. Like I said, first time I experienced an issue like that. Brake booster (’95 XJ) and proportioning valve (’88 XJ) were NOS.

 

Plug for the Motive Bleeder. I’ve been using mine for at least 20 years and it’s great. They sell different auto manufacturer caps to work with their main canister.

 

[Gjeep]

Finally got to it – AC is charged; R134a conversion using factory ’95 XJ parts as in my other MJ. Hard to tell how cold it truly blows as it’s at best 50* here currently. If the temperature gun I used was correct, the MJ was blowing 38* yesterday but want to confirm. Will retest. Where’s the sun when you need it... Testing the HVAC wasn’t without its challenges, as I could get the bezel control to open/close any of the doors. Pulled the vacuum lines off the back of the bezel and nothing. Assumed a vacuum leak but couldn’t find any. After walking away for a bit I thought I’d take a double-take at the check valves – one off the intake manifold and the other near HVAC side firewall. What was there I didn’t recognize. I pulled them both and noticed how tiny the port was where vacuum passed. Replaced them both with parts bin factory check valves and all started working again. Curious though for any who own a ’91 MJ if yours has these same check valves from the factory. I don’t recognize them.

 

 

 

First pass at drilling holes on the lightbar I’m building out of an XJ roof rack, and everything worked out. I’ll be running wiring through the driver’s side channels near invisibly. You can see the small hole in the end cap it will run through then into the roof. They still need to be cleaned up and painted.

 

 

 

 

Also got to rewiring the IPF headlight harness as it doesn’t play well with the Holley RetroBright headlights I’m going to be running. The IPF harness is great for standard headlights but doesn’t run its power correctly for the MJ to use RetroBrights with it. Kudos to Red Mistress for giving me the heads up on these. All my Jeeps will be getting a set.

[Eagle_SX4]

4 hours ago, Gjeep said:

Curious though for any who own a ’91 MJ if yours has these same check valves from the factory. I don’t recognize them

Those look to be dorman check valves. Which seem to be the most available aftermarket ones.

[Gjeep]

I finished cutting and drilling on the XJ roof rack – it wasn’t nearly as challenging as I thought it would be. Got lucky. It came out well but still need to refinish these parts and nutsert the roof/ run wiring invisibly. This MJ will be running NOS Wrangler TJ rounds in front and up top.

 

 

 

I decided also that I want some thump in the MJ. I ran this same Pioneer unit in my other Comanche, but two of them tucked behind the seat track versus under. Unfortunately, the driver side doesn’t have enough room under the seat track thanks to the girthy tunnel. And since this is meant to mostly be a work truck I’m only running one sub this round. It will be disassembled and painted black to match the rest of the interior even though it's tucked away.

 

[Gjeep]

Just as I straightened up the driver side wiring, I made a mess passenger side. The under the seat Pioneer sub is installed (140W). It’s nothing crazy but adds decent thump when needed.

 

 

RediRad is the aux unit I installed in my other Comanche that got me to BlueTooth. Last time I spoke to the owner (husband and wife team, product made in USA) close to 4 years ago they were closing their doors… so I purchased a round of the latest aftermarket BT add-in’s over the past couple weeks, tested them out and they all sounded like crap with the stock head unit. Took a gamble at reaching out to the RediRad mom & pop shop and found out that they reopened due to the demand half time while looking to expand. I wasted no time buying one of their units. Basically, it’s a go-between on the co-ax cable/ FM modulator with ignition-sourced power and ground. That’s it – and you get a 3ft long aux cable to plug in to your phone/ device. From that point I added a USB BT, ground loop noise isolator, splitter and then a hard wire USB/aux run going inside the center console that powers the phone and serves as a hard wire option for music. I have the option of BT or not.

 

[ghetdjc320]

Out of curiosity, have you seen the Focal under seat passive subs? I was seriously looking into these as an option when I was sorting audio. Not sure how they would work with the stock brackets though. I measured them for my corbeau brackets and they looked like a perfect fit. 

[Gjeep]

Sure did -- too big. I was at first open to some trimming of the factory seat bracket but the amount that needed to be removed would make the seat no longer safe. Possibly trimming the repop MJ brackets that are a much thicker gauge metal could work, but in the end for my needs these Pioneers sound good especially when running 2 of them tucked under the backside of the seat/floor as in my other MJ. I don't know about the Corbeau brackets and what kind of space is under there. There is an odd but do-able option of running the first gen seats on 2nd gen brackets. I recently saw an adapter online to make that happen. You'd also need to add in the mounting crossmember both driver and passenger side floorboards -- but there would be enough room as I'm running similar sized subs in my kids newer XJ's and they have plenty of room. Again, an odd option. But an option. 

[Gjeep]

While I was rewiring my IPF headlight harness to work with Holley RetroBright’s, I was reminded while testing that our GM column'd trucks don’t have the modern ‘flash to pass’ feature. I did some research and found a site where it's added to an ’88 C/K using an early ‘90’s Cadillac DeVille/ Fleetwood dimmer switch that is identical – you only need to add a 12V wire into the connector. Easy enough. I’m using Standard Motors part# DS-203. (Note: you need to pull the thin retaining clip at final installation.)

 

 

[eaglescout526]

37 minutes ago, Gjeep said:

did some research and found a site where it's added to an ’88 C/K using an early ‘90’s Cadillac DeVille/ Fleetwood dimmer switch that is identical –

I found out that this was added to our Jeeps in 89. The TSB book I have from 89 says that some early models are wired the old way from the previous years and that the wires need to be swapped. I forget which wires it was that needed to be swapped but since yours is a 91 it’s good to go. 

[Gjeep]

Interesting -- I'll check out the connector on my '91. Odd they didn't just pop in the flash to pass switch then.

[fiatslug87]

My ‘89 and ‘90 have that functionality, pull the stalk towards you and the high beams come on before the click of turning them on, release and they turn off, the ‘88 does not.

[Gjeep]

My '89 had it, my '92 has it, but my '91 does not... and I just figured out why. This NOS steering column is 1987 vintage, so it makes sense. I just looked at the original steering column and it indeed has flash to pass. This will be more or less plug and play. 

[Gjeep]

Adventure of day was getting the light bar secured. Two seam-sealed nutserts per side were put into place with all the light bar components freshly painted (yesterday). The nutserts are not visible from inside the cab as there is inner support from a-pillar to b-pillar so they won’t be poking into the headliner once installed. Wiring connects at the driver side b-pillar light and has been rattle-free wrapped and tucked away inside the b-pillar.

 

 

 

 

Also got the third brake/ cargo light installed. I have the cargo light tied into the interior lighting of the truck. Never was a huge fan of how Jeep had that as a separately switched item. Additionally, I want to keep the right-side switch pod empty/ available should I decide to add a winch in the future. Left of steering column switch pod has the bumper fog lights and efan manual override switches. I’ll move the truck outside in a couple days as rain is expected for the next couple weeks to see if there are any leaks. Then onward to installing the headliner and rest of the interior.

 

 

Last but not least, I disassembled the Pioneer subwoofer and painted it black. That blue/gray color with Pioneer logo wasn’t going to work. Beautiful.

 

[Gjeep]

I took some time to ponder on the engine vac lines and how they’ve been run. Originally, I followed the web on how best to install with the U-shaped manifold on the OBD1 MJ’s and XJ’s…meaning cap/ do not use the large side center vacuum port of the manifold. Having some vacuum line issues/ cracks discovered on this build I decided it best to run a 99+ XJ firewall vacuum hard line (with check valve added in) that connects to that large side/center port and serves as the dedicated engine HVAC and cruise control main supply. Plenty of vacuum. And as a bonus, the newer line is a slightly larger diameter than original MJ one and extends forward from the firewall at the heater core a good 5” so it’s not laying on top of or near the heater core hoses. The MAP sensor has a dedicated intake top side port and the charcoal canister small line and rear of valve cover PCV share a smaller port on the side of the intake on this truck. Engine purrs. Will be revising my Stroker MJ vacuum lines similarly.

 

 

 

I’ve always preferred the angle of the AW4 shifter on the 97+ XJ’s. When I first got my ’01 XJ long ago I couldn’t immediately figure out what it was about the seating position that was different from my ’95 XJ when shifting between gears. Took me a minute to figure it out and then realized the newer XJ’s had a bend to their shift lever. Many, many moons ago I grabbed a couple of the newer style shift levers in the wrecking yard just in case I got an AW4 MJ…and then 20+ years later I got one. Here are the two shifters front/ back showing the difference. I needed to drill out the console bracket to put on the newer shifter (and cut a bracket off the newer setup that is for the second gen console). Done.

 

 

[Gjeep]

I was determined to get the dashboard in – and 5hrs later it’s done! Ready for 2026 now. No doubt I could have gotten it in faster, but I took my sweet time as I didn’t want any damage. Also, I wanted the wiring to line up properly, and ziptie it to the behind the factory mounting points. Forgot how much fun this is... head up under the dash and hands looking like they were attacked by a feral house cat. I’ll call it 98% installed… I still need to shift the dash 1/8” to the right to center steering column dead-on. This dash (and entirety of the black interior) came from a parts MJ I bought back in 2019 off Craig’sList in North Carolina. Its interior was minty so I shipped it to the west coast to strip it down. It was a farm truck, a black ’86 XLS 2.8L, 5-speed 4x4 with 75K on the clock. It ran well but turned out to be a gross polluter, so I decided at that point she wasn’t a keeper. But before selling it, I taught all 3 of my daughters how to drive stick on it. The interior was gutted, nothing but a steering column and seats. My wife was horrified, but they learned. That truck was nicknamed ‘The Beast’.

 

 

 

 

 

Goodbye tan, column shift, bench seat interior.  Next up, getting the headliner and overhead console in, as well as recovering the visors and installing those.

 

[Gjeep]

Continued assembly of the dash… Factory radio in place with BT connectivity a la RediRad unit which fits perfectly in the ‘Y’ opening of the defroster duct up against the firewall. The AC bezel, gauge cluster, first gen clock, cigarette lighter, and rocker switches (fog lights and efan override) in place and working as they should. Was stumped at first as to why headlight switch wasn’t turning on the interior lights when I clicked left– then I remembered the ground. Important. For the efan override rocker, I always use the face of the XJ rear wash/wipe (which is identical to the fog light switch except it does not have the notification ‘on’ light) because for the HO era XJs/MJs the efan is triggered off the PCM by a ground. So, no light would be illuminated when switched on.

 

 

[Gjeep]

Headliner is up and carpet dropped in. Final trimming is work in progress to get fit 100%..

 

 

[Gjeep]

Finally done trimming the carpet/ getting whatever electrical that needs to be through into place and test-fit a scrap center console for any gaps. Always a pain-staking process with the carpet, as typically the mold is off somewhere. It seems ACC must start the stamping process on the passenger side because the driver side is 99% of the time where the contouring with a heat gun needs to be done…this goes for both MJ’s and XJ’s. BUT, I’m thankful they’re still producing these for our builds.

 

 

New 97+ XJ door seals were used on this build as with the other as the larger, oblong seals just seal better both noise and the hose. I re-hung/ shimmed the driver door as the gap was off, driving me nuts. For the a-pillar exterior, I split the difference between the new and the old-style seals, using a 3M weather stripping near identical to the ‘97+ XJ cowl to hood seal. It fits well and looks OEM.

 

 

 

 

[Gjeep]

Overhead console has been assembled, installed and working. The front of it is hung similar to the XJ, though the XJ bracket has been bent to follow the higher Comanche’s roof line. The rear is kept in place using a cut-down SJ bracket adhered to the roof and attached via the same screw/ mounting hole the Wagoneer uses in the sunglass bin. Time to cover the sun visors…