1990 Mack RD wiring info

[IceHole]

Anyone know where I can find wiring diagrams for a 1990 Mack RD?

Someone, or several people butchered a bunch of wiring.

I’ve removed most of the added stuff... complete with house wiring, extension cord, black taped splices, etc.

Still have no headlights other than there's a "courtesy flash" switch on the dash and it works. Also no dash lights, though that's less important.
Oh, and tail lights are always on.

Even just a pinout of the headlight switch would help.

The wiring is a nasty mess of oil and dirt... Mack ran the oil pressure guage pressurized oil line direct to the gauge. WTH?! and the air switches all vent in the dash.

 

[Truck Shop]

Direct pressure to gauge is really common. With Freightliner COE's years ago the old joke
was you could tell the Freightliner drivers at the truck stop--top front of boots were oily.
Plus depending on how air system was plumbed and type of air switches used they can
exhaust at switch.
*
I have a late 80's Mack generic wiring schematic but I'm having a issue finding it.

 

[kshansen]

Not sure of the year this was from but best I have. It was too big to fit on scanner so I scanned it as two images. One could print out both images and then splice they together. Also I scanned at a good resolution so if view on computer it should be easier to read.

Like Truck Shop says this is a "generic schematic" so it shows many different options. One in particular is the starting/battery section showing four different electrical start arrangements and eve one air starter arrangement! Also four different charging systems!

Looking closer at it it does have the circuits for anti-lock brakes so can't be too old!

Worst thing is it is on light gray background which doesn't help the clarity.


Note there is a little over lap where the images fit together!

 

[IceHole]

Thanks!

Got the headlights working, dimmer was bad.
Not sure why when testing i only had like 3 volts at the breaker.

No dash lights still, pto light, and voltage gauge randomly works and doesn't.
When it's working the heater blower usually works, if it's not, no blower.
Oh and tail lights are always on.

No idea what people were doing with playing with wiring but it's scary "work".

 

[heymccall]

Main power relay is suspect.
Everything you say "works intermittently" is fed by that relay.
Headlamps are not.
Looking through glove box, relay is left of fuse panel, on firewall.

I've changed quite a few. The tattletale is no blower when other stuff quits.

 

[IceHole]

Was that relay. Thanks!

 

[IceHole]

Waiting on a relay to come in to further troubleshoot. I can get it to work by hammering on it haha.
Was 1/3 of the price online vs local.

Need to figure out why the key on has the brake lights stuck on. Thought it was tail lights but parked it in the dark and could better see bright vs dim. With the key off, the tail and brake lights work correct.

Also there's clearance lights on a switch and park/headlights on another. Only thing the clearance light switch does is light up the 2 outer cab roof lights. That correct?

Park lights lights the 3 middle, fenderlights, dump box corner lights and the tail lights.

In the dash there's a "spider" with bare wires that goes to the switch labels, to I think light them up? Assuming that's the ground for those and power is from?? Debating just cutting that wiring out if it's non functional.

 

[heymccall]

Brake lights on at key on are because park brake is set.

Clearance switch for outer roof lamps only is a Mack thing.

Spider thingy is fiber optics to glow the switch legends. Follow to common point, remove lamp socket, and replace bulb.

 

[cfherrman]

The outer clearance lights got me one time, was funny

 

[IceHole]

The outer clearance lights got me one time, was funny

I spent a bit fighting mosquitos checking the bulbs, switching them with known good, called it quits and had a last second, huh I wonder.

I was guessing it's something the previous owner did, every other truck I've run with separate switches lights more than just 2.

And I've never seen a truck keep brake lights on with the park brake, that's an odd one.

 

[IceHole]

Brake lights on at key on are because park brake is set.

Clearance switch for outer roof lamps only is a Mack thing.

Spider thingy is fiber optics to glow the switch legends. Follow to common point, remove lamp socket, and replace bulb.

Thanks for the info.
None of the dash lights work so need to sort that out. They were mostly pulled out of the gauges even.
Not a high priority vs exterior lighting though.

Sure is a head scratcher to decipher goofy Mack stuff and WTF doings of other people.

 

[cfherrman]

A lot of the new trucks put the brakes lights on with the park brake, then when you turn the transmission (and not the rears, transfer case) with the brake on the dash beeps at you all day

 

[heymccall]

I think I has same schematic

 

[Truck Shop]

I was guessing it's something the previous owner did, every other truck I've run with separate switches lights more than just 2.

And I've never seen a truck keep brake lights on with the park brake, that's an odd one.

Items unique to Mack since the first RL in 1966.

 

[IceHole]

Has the Mack 12 speed.

Anyone familiar? Every shift pattern I fine has low in the middle and high to the driver (either it's low and direct or direct and hi it seems).

Mine seems like low is toward the driver best I can tell.
The lines on the shifter have different fittings so doesn't seem like they could easily be crossed up. Not sure on the trans, would need to flex in ways I can't and see through years of grease and goo.
Spent 4+hrs steam cleaning it last fall and could probably spend another 4 hours.

PTO operation. This trans has a drop box on the back for PTO, doesn't use either pto port on the sides.
I can't find any specific info for it. The book I found on the TRXL107 series say to use double neutral for PTO use.

 

[cfherrman]

The mack special pto's I've used has a neutral switch on the dash and then you would grab a gear to change the speed of the PTO. I don't know what double neutral is but I'm guessing you hit the switch and let the shifter in neutral.

 

[IceHole]

The mack special pto's I've used has a neutral switch on the dash and then you would grab a gear to change the speed of the PTO. I don't know what double neutral is but I'm guessing you hit the switch and let the shifter in neutral.

Neutral shift lever and Neutral on the range selector (low, high, Neutral, reverse)

No neutral on the dash, just PTO on/off air switch.

 

[cfherrman]

I think I drove one with two sticks like your saying. I would guess it's like any other pto and can have it in regards if a gear is grabbed or not. If it doesn't work have range in neutral and grab a gear with the shifter

 

[IceHole]

I think I drove one with two sticks like your saying. I would guess it's like any other pto and can have it in regards if a gear is grabbed or not. If it doesn't work have range in neutral and grab a gear with the shifter

Maxitorque 12 speed. Trxl1070 I think.

It works fine, just was wondering if neutral on the range matters.
The PTO runs off the back of one of the countershafts and has a ~2ft driveshaft to the pump.

 

[cfherrman]

I have no idea, I'm guessing that if you leave the range in there is more stuff spinning and more wear.