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1989 mh ground


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I do not know without looking at the schematic. I am in OH and will try to look later this week when I am back in PA with my truck. What is your problem with the dash?

Ken

HOF City, PRR Country, and Charter member of the "Mack Pack"

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volt meter and fuel guage are reading very low. checked voltage at volt guage and was ok but the ground side was low. the ground wire from the frame up to the cab was ok so figured was getting a bad connection at the junction terminal in the cab

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My fuel gauge was acting erratic. I put a ground wire from the gauge to a mounting screw on the circuit board. That solved my issue. I have "static" in my satelite receiver and I suspect it is a "bad" ground somewhere.

Have you used a good ground to the gauge and determine if the issue is resolved?

Because of the fiberglas cab, ground is always an issue with MHs.

Ken

HOF City, PRR Country, and Charter member of the "Mack Pack"

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I found the electrical manual for the MH. I see no common ground junction for the dash or cab. The LH Gauge Panel A and RH Gauge Panel C have individual grounds but a common ground wire within each panel (lights and gauges). The ground wire is an 18gauge Black. If I remember correctly, the gauge panel ground circuit is on the printed board. Do all your gauges and dash lights act strange? If not then I would say (SWAG) it is the individual gauge circuit. If it were a cab ground likely all the gauges and lights would be an issue. Like I stated earlier, run a jumper wire from the gauge ground to the panel screw. Or a good ground from the panel.

Sorry I can't be more help. I will look at my MH when I get to PA later this week.

Ken

HOF City, PRR Country, and Charter member of the "Mack Pack"

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with a multimeter across the voltmeter terminals i only got 10v but if i take the ground lead to the frame i have 12.5v so i know i got a bad ground. the ground wire from the frame up to the cab is about a 6 guage wire which would make me believe it junctions in the cab somewhere to the other circuits. i have had an instance where the left turn signal had back feed to the warning lamps on the left guage panel which would make me think it was looking for a ground

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Per the Isometric drawing, item 49 is the cab ground... it appears to be located just below and behind the centre of the dash...

not seen that on mine but would assume it to be a stud... the wire appears to feed through the harness to the multi-plug connector next to the air-line connector block below the cab... and the chassis ground is just beside the left steering box (I have seen that on mine)...

as Farmer 52 has mentioned, jumper to any good ground source to see if it corrects the problem... you may have poor connections within the dash panel. Repair maybe a new jumper from the gauge.

Plastic cabs and electrics are a problem....

BC Mack

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I agree, ground issue but finding it another story. There are a lot of connectors under the dash but again I do not see a common connector for the cab. My only suggestion is to start with the main connector and work from there. The schematic shows individual grounds but no common connection.

If you don't have a schematic I will try to scan mine and email to you.

Electronics....don't ya' just love them!

Where are you located?

Ken

HOF City, PRR Country, and Charter member of the "Mack Pack"

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Per the Isometric drawing, item 49 is the cab ground... it appears to be located just below and behind the centre of the dash...

not seen that on mine but would assume it to be a stud... the wire appears to feed through the harness to the multi-plug connector next to the air-line connector block below the cab... and the chassis ground is just beside the left steering box (I have seen that on mine)...

as Farmer 52 has mentioned, jumper to any good ground source to see if it corrects the problem... you may have poor connections within the dash panel. Repair maybe a new jumper from the gauge.

Plastic cabs and electrics are a problem....

BC Mack

Thanks BC, I see item 49 but I agree with you...poor connections within the dash panel (perhaps on the circuit boards). If all the gauges, lights, etc. are erratic it is likely a cab ground issue. If only a select few gauges, etc. then an internal ground.

Ken

HOF City, PRR Country, and Charter member of the "Mack Pack"

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My 1989 MH was doing the same strange things as yours when I drove it home after sitting for about 10 years. Take the center section of the dash out-where the tach and speedo are located. Buy some contact cleaner and clean the male and female connectors and your problem will probably be solved-mine was. I think I used Q Tips in some hard to reach areas on the connectors. My toughest problem was getting the cables off the tach and speedo. You will not have much room to pull them out but the cables will come off the back of them.

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Most of my electrical problems for either of my MH's traced back to the large silver 30 pin connectors behind the LH head lamps (large deutsch body wiring plugs) Tons of problems with corrosion and (Ontario road salt) getting into connectors. Loose pins as well. I've had signal problems through that plug. If i remeber correctly, are there grounds that come back down through some of those plugs?

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I am not aware of any 30 pin connectors behind the left head light. The dash connectors definitely have the ground circuit on the pins. You get erratic lights or indications when the ground is completed through another connector. Do your MHs have the connectors behind the tach and speedo like the picture of mine above?

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I am not aware of any 30 pin connectors behind the left head light. The dash connectors definitely have the ground circuit on the pins. You get erratic lights or indications when the ground is completed through another connector. Do your MHs have the connectors behind the tach and speedo like the picture of mine above?

the connector is buried behind the hoses in this pic..... the only time you would need it is to remove the cab.

we have the same corrosion issues here in BC... when I was out looking for an MH a former Mack dealer foreman gave me a list of three or four things that were always an issue on the MH, and that plug was number one on the list.

that hose and wire bundle in the sleeve guide over the left steering box is worth pulling apart and power washing, I have found salt galore, and a 6ga positive wire chafed through to copper.

It amazes me that Mack put the starter solenoid just above the left front tire and simply wrapped it in rubber mat.... hmmm

BC Mack

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  • 3 weeks later...

Warning: Off topic

i ran a 2002 granite triaxle roll off on the farm for a bit, and the fuel gauge read how much air was in the tank......useful after i found out the hard way.....at least i was on top of the hill, and the fuel at the bottom. pain in the ass to "strong arm" a class 8 tho.

Sadly, i quit there before the problem was resolved, then the truck was traded i n on another mack (was chattin with one of the drivers)

Lack of planning on your part does not constitute an emergency on my part....

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  • 4 weeks later...

sorry, been busy. the problem was at the connectors at the guage circuit boards where the harness plugs in

The connectors behind the speedometer and tachometer per MHfred?

Ken

HOF City, PRR Country, and Charter member of the "Mack Pack"

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Just a note about grounds looking ok. I worked on a '07 Chevy C5500 Passanger bus with multi electrical/computer issues that fried computers (ECM and TCM), caused intermittent Check Engine lights, and eventually burned up the alternator. All the grounds looked ok to the naked eye until you unbolted them and realized the through holes were drilled and powder coated before the grounds were installed with the "star" washers only creating the ground when snugged down. Needless to say over the past 6 years some corrosion and rust started on those tiny spots where the washers dug into the powder coat causing a loss in contact. A quick hit with an abrasive disc and some battery terminal spray on the spots made the grounds contact again. All the issues them went away. Just thought I mention a recent experience.

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