Author Topic: How to hook up starting batteries on 68 MC5A  (Read 513 times)

Offline mc5a Jon

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How to hook up starting batteries on 68 MC5A
« on: May 05, 2021, 07:41:05 PM »
My bus has sat for 10 years. I took out my batteries years ago (to prevent theft) and don't remember for sure how they were hooked up. The cables have red and black sleeves... but I seem to remember that didn't mean red + black -. I've just freed all the injectors. I've drained some of the old fuel... by removing the drain plug from the tank. It stinks but no water in it or algae. And bought new 8D's. Just don't want to hook up the batteries wrong. Any advise?

Offline chessie4905

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Re: How to hook up starting batteries on 68 MC5A
« Reply #1 on: May 06, 2021, 04:13:00 AM »
follow cables some. Is there a disconnect switch or do any cable attach to chassis?
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Offline hogi6123

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Re: How to hook up starting batteries on 68 MC5A
« Reply #2 on: May 06, 2021, 07:05:37 AM »
Is the bus 12V or 24V?  Hookup is very different in each case.

Assuming 24V negative ground:

You have 2 8D batteries?  Each battery is 12V. There will be a short cable that hooks the + of one battery to the - of the other one.  That makes one large 24V battery out of your two 12V batteries.  There might also be a wire or several that connect to that cross connector, it supplies 12V.  If you have a battery equalizer a wire connects from here to the 12V bolt on the equalizer.

Now, there should be two remaining large wires from the bus, one black and one red.  One end of the black lead should be bolted directly to the chassis of the bus.  That wire is ground and connects to the not yet used - post of the two batteries.  If you have a battery equalizer, a wire connects from this wire to the ground bolt on the equalizer.

The other wire should be red and run to a large master disconnect switch. That wire is 24V and connects to the not yet used + post of the two batteries.  If you have a battery equalizer, a wire connects from this wire to the 24V bolt on the equalizer.  There may be a few other small wires that connect to the 24V post as well.

If you're not sure where something should hook up, don't hook it up!  Find out for sure where it goes before hooking it up.
1981 MC-9
1994 102DL3 (parts bus)
Central IL

Offline mc5a Jon

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Re: How to hook up starting batteries on 68 MC5A
« Reply #3 on: May 06, 2021, 08:48:11 AM »
The bus has a red and a black cable for each battery. Batteries are on a rack on top of each other aft of the fuel tank. All 4 cables bolt to the wall in the battery area. There is a disconnect in the RH fwd baggage compartment fwd wall. How do I make sure Red goes to positive and black goes to negative BEFORE I hook it up!

Offline mc5a Jon

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Re: How to hook up starting batteries on 68 MC5A
« Reply #4 on: May 06, 2021, 09:00:23 AM »
The bus is 24 volt no small cables.

Online richard5933

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Re: How to hook up starting batteries on 68 MC5A
« Reply #5 on: May 06, 2021, 09:06:39 AM »
...How do I make sure Red goes to positive and black goes to negative BEFORE I hook it up!

Continuity tester
Richard
1974 GMC P8M4108a-125 (Custom Coach "Land Cruiser")
1964 GM PD4106-2412 (Former Bus)
Located in beautiful Wisconsin
KD9GRB

Offline Dave5Cs

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Re: How to hook up starting batteries on 68 MC5A
« Reply #6 on: May 06, 2021, 09:49:55 AM »
My 5C looking at the two trays.
Upper left is neg upper right is pos
Lower tray
left is pos and right is neg. :^
"Perfect Frequency"1979 MCI MC5Cs 6V-71,644MT Allison.
 1998 Jeep TJ , Somewhere in the USA fulltiming.
Congressmen should wear uniforms, like NASCAR drivers, so we could identify their corporate sponsors

Offline hogi6123

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Re: How to hook up starting batteries on 68 MC5A
« Reply #7 on: May 06, 2021, 10:21:05 AM »
The bus has a red and a black cable for each battery. Batteries are on a rack on top of each other aft of the fuel tank. All 4 cables bolt to the wall in the battery area. There is a disconnect in the RH fwd baggage compartment fwd wall. How do I make sure Red goes to positive and black goes to negative BEFORE I hook it up!

I would assume red=+ and black=- for each battery.  If I wasn't certain, I would try to visually trace the wires.  If that fails, a continuity tester or multimeter (ohms scale) can help determine which wires are connected to what.  One of the 4 should be continuous to the bus chassis (ground), one should be continuous to one side of the main shutoff (24V), and one from each battery should be connect to each other and not to the ground or main shutoff.  Make sure none of the ends of the cables are not touching anything metal while testing, rest them on a piece of cardboard or something like that.  Also this test needs to have nothing else connected, definitely the main switch in the Off position.

If you can post a few detailed pictures, that  might be helpful too.
1981 MC-9
1994 102DL3 (parts bus)
Central IL

Offline mc5a Jon

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Re: How to hook up starting batteries on 68 MC5A
« Reply #8 on: May 06, 2021, 03:57:06 PM »
I will try to get picts, but you all have given me what I need to figure this out! Thanks! I'll get to it tomorrow. I'll let you know.

Offline Utahclaimjumper

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Re: How to hook up starting batteries on 68 MC5A
« Reply #9 on: May 06, 2021, 05:17:55 PM »
 Dave,,, your description totally depends on which way his batteries are placed in the trays..>>>Dan  ( He could sort it out quickly if he new even the basics of using a VOM.)
Utclmjmpr  (rufcmpn)
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Offline mc5a Jon

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Re: How to hook up starting batteries on 68 MC5A
« Reply #10 on: May 07, 2021, 10:02:35 AM »
Dave, I took your description to mean the upper LH cable on your bus goes to the Neg battery terminal. Upper RH goes to the Pos terminal. Lower LH goes to Pos terminal. Lower RH goes to Neg terminal. It wouldn't matter which way the batteries were installed. I will ohm out to make sure mine is the same before connecting. All the cables going through the walls threw me off! Thanks for all the help. I'm trying to get out there and do this today...Just got other things going.

Offline mc5a Jon

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Re: How to hook up starting batteries on 68 MC5A
« Reply #11 on: May 07, 2021, 04:29:09 PM »
The batteries hook up just like Dave said. Thanks Dave! I did double check with VM before connecting. She fired right up! But I think I lost fuel prime cause she only ran for about 45 sec. Then cranked but no start.

Offline Dave5Cs

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Re: How to hook up starting batteries on 68 MC5A
« Reply #12 on: May 08, 2021, 06:52:31 PM »
Welcome now change your fuel filters and try again. :^
"Perfect Frequency"1979 MCI MC5Cs 6V-71,644MT Allison.
 1998 Jeep TJ , Somewhere in the USA fulltiming.
Congressmen should wear uniforms, like NASCAR drivers, so we could identify their corporate sponsors

Offline mc5a Jon

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Re: How to hook up starting batteries on 68 MC5A
« Reply #13 on: May 11, 2021, 03:24:41 PM »
Will do!