MH master kill switch area

[Mack Doctor Jr.]

On the MH there is a box above the drivers tire with the master kill switch and the starter solenoid. Mine is 24 volt cause it has an E9. Would anyone have a diagram I can get a copy of. I need to rewire it, or can I just some how leave it out and convert it to 12 volt?

Has anyone done this on an MH? I'm sure it may cost a little to do but I think it will make things a little easier in the long run.

[gearhead204]

I just did mu superliner in august 24 to 12 was fairly easy needed a 12v starter and volt meter had borrowed a shop book from the construction co. that I used to work for and it had all mack elec. combomations listed on one schematic, if you can get to a dealer you should be able to copy what you need.

[BC Mack]

I have an E9 in my MH and it is 12V.... 24V is as an option and not an "E9 given" as you state..

you have checked the batteries and wiring to confirm 24V.. ?? there are 4 batts on both systems. use a voltmeter to check what you have.

is there a reason you need to change, are you having problems??? easier to repair your issues than modify.....you can just bypass the master switch if that is sticking... that won't affect anything unless you have an overnight drain.

anyway, to answer your question on modifying here are some basics but not everything....

adjust interconnections between batts

change starter motor to 12V by replacing it..

the alternator will need to be configured to supply only from 12V stud, or replaced.

24V start needs less amps and usually has smaller cable but drawing shows Mack has installed same 000 cable on both types, saved you some money.

the MH electrical system manual can be found on ebay, given your need it may be a good investment before you start ripping the truck apart.

I have attached 24V info from the Mack manual to help you find your problem, if you have a 24V system.... if you have 12V I should be able to put the drawing on my scanner

keep us informed...

BC Mack

[Mack Doctor Jr.]

Thanks BC. The solenoid went bad and I can't find the exact one and the others don't like to fit in there.

I have 24 volts on one of wires so it's wired right. With the new one on it now it won't do a thing.

[Marcel67]

I bought my solenoid at the Mack dealer here in Miami. Also have the E9 engine and 24 v system

[Mack Doctor Jr.]

Do remember what the part # was on that marcel?

[kscarbel2]

I have an E9 in my MH and it is 12V.... 24V is as an option and not an "E9 given" as you state..

BC Mack

With respect, that's not accurate. 24-volt starting was standard with E9 V-8 powered Mack Trucks, and for a very good reason. You want the "kick" of 24 volt starting, the preference worldwide, for turning over a 16 liter engine, particularly in cold conditions.

You are doing yourself a disservice if you change an E9-powered Mack truck's starting system over from 24 to 12 volts.

Call Watts Mack with your truck's unique model and serial number (located on the vehicle identification plate) and allow them to order you the correct part.

Note the E9 engine options below, and note 1.

[BC Mack]

Hi KSCarbel....

I certainly don't dispute your info, you are a guru.... it is 1988 data and all the E9 MH's I've looked at were very late models, mines a 93 and built with the Canadian climate in mind... so I formed my logic / judgement from that alone.

I'll withdraw my statement then...

keep up the good work

BC Mack