'78 Bus Alternator Test

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Gypsie
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'78 Bus Alternator Test

Post by Gypsie » Tue Aug 25, 2009 9:44 am

Quick question about testing for alternator function.

I am not sure the alternator is working on a 78 bus.

The light does not come on on the dash before start, for one thing, but likely unrelated.

Is it not possible to test for function by volt metering before start at the positive of the coil (ie- ignition on, one probe grounded and one on hot at coil) to get an initial voltage, and then after starting get another reading. After starting there should be an increase with the juice from the alternator?


Also can anyone scan a fuse block page and the wiring diagram for a 78 FI bus.

Trying to avoid buying a Bentley for a bus I don't own.
So it all started when I wanted to get better gas mileage....

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dtrumbo
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Post by dtrumbo » Tue Aug 25, 2009 10:06 am

The wiring diagram is online here.

http://www.thesamba.com/vw/archives/inf ... _77-78.jpg

Image

The key is here.

http://www.thesamba.com/vw/archives/inf ... 78_key.jpg

Image

Your test procedure is valid, except I would test the voltage at the battery instead of the coil. Nothing in the way that way.
Gypsie wrote:The light does not come on on the dash before start, for one thing, but likely unrelated.
Not so, the light has to work in order to provide excitation voltage to the alternator. No light, no charge from the alternator.

Good luck!
- Dick

1970 Transporter. 2015cc, dual Weber IDF 40's
1978 Riviera Camper. Bone stock GE 2.0L F.I.
1979 Super Beetle convertible.

... as it turns out, it was the coil!

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RSorak 71Westy
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Post by RSorak 71Westy » Tue Aug 25, 2009 10:50 am

At rest not running you get about 12.3 volts. Running with a good alt. you should see at least 14 volts.
Take care,
Rick
Stock 1600 w/dual Solex 34's and header. mildly ported heads and EMPI elephant's feet. SVDA W/pertronix. 73 Thing has been sold. BTW I am a pro wrench have been fixing cars for living for over 30 yrs.

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hambone
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Post by hambone » Tue Aug 25, 2009 11:59 am

Yeah, don't you just test at the battery terminals?
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Gypsie
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Post by Gypsie » Tue Aug 25, 2009 1:40 pm

I will use the battery. It's kind of tucked away but the positive terminal is easily reachable. The coil is right there and requires less contortioning.

Thanks Dick for the diagrams and links.

The first steps I will make for the charging system will be to track down the dash light issue to make sure the connections are good and...uh...connected.
So it all started when I wanted to get better gas mileage....

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AirCooledNut
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Post by AirCooledNut » Wed Aug 26, 2009 8:55 pm

Check the bulb, make sure it's not just burned out -- you need to operate on vehicles the same way I look for women, cheap and easy first! (Okay, just kidding...you breathe a word of this to my fiancé and I'm dead meat!) :blackeye:
Toby http://www.aircoolednut.com/
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AirCooledNut
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Post by AirCooledNut » Wed Aug 26, 2009 8:57 pm

hambone wrote:Yeah, don't you just test at the battery terminals?
Since the stock alternator B+ wire goes to the big terminal on the starter, you can also check there. The other big wire on there goes to the battery :wink: you know, if you like crawling under a Bus and gettin' grimey
Toby http://www.aircoolednut.com/
Did I mention that I'm an original Darksider?
DDB Forum
'72 VW Squareback, 2007cc, GB 5-speed, rag top; '76 VW Riviera Sundowner; '95 VW Jetta GL, Solo II EP; '81 Goldwing 1100
http://www.frappr.com/type3volkswagenowners & http://www.type3registry.com/

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