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1988 GMC P (motorhome) Chassis electrical
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Dennicorco
Novice
Oct 22, 2006, 2:31 PM
Post #1 of 8
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1988 GMC P (motorhome) Chassis electrical
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Help! Can anyone tell me what the three wires coming off the back of the alternator on this beast are for. I am talking about the ones on the terminal. (Not the red HOT wire all by itself). Two of the three are tied into a main harness but one, (White with black stripe) is hooked to nothing. I am experienceing a no charge of the chassis battery. have had alternator tested twice good, new battery and still no charge to chassis battery. all suggestions welcome. Also, I cannot locate fuse link either.
Dennis
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DanD
Veteran
/ Moderator
Oct 23, 2006, 5:00 AM
Post #2 of 8
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Re: 1988 GMC P (motorhome) Chassis electrical
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You’ve said the chassis battery? Do you mean that there are two batteries one for the accessories in the home and one for starting the engine? If there are two batteries then are both not being charged?
Dan.
Canadian "EH"
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Dennicorco
Novice
Oct 23, 2006, 7:37 AM
Post #3 of 8
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Re: 1988 GMC P (motorhome) Chassis electrical
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Dan, Motorhome has a "house" battery and a chassis battery. The problems are with the chassis battery. Thanks, dennis
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DanD
Veteran
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Oct 23, 2006, 9:59 AM
Post #4 of 8
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Re: 1988 GMC P (motorhome) Chassis electrical
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Here’s a wiring diagram of what I hope is the proper one for yours. It’s been a long time since I’ve worked on or with this style of alt or its circuit.
Hope it helps but at times when they converted these trucks into motor homes they also changed some of the wiring to accommodate the home’s needs. This diagram also shows gas and diesel applications so don't mix them up.
Dan.
Canadian "EH"
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Dennicorco
Novice
Oct 23, 2006, 2:09 PM
Post #5 of 8
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Re: 1988 GMC P (motorhome) Chassis electrical
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Dan, Thank you so much. Its been so cold here I haven't been able to go out and work on this for a couple days. Hoping this weekend brings a bit warmer temps.
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Dennicorco
Novice
Oct 26, 2006, 11:35 AM
Post #6 of 8
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Re: 1988 GMC P (motorhome) Chassis electrical
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Dan, I just came in from doing multiple diag checks on this vehicle. I can tell you all the fuse links are testing for good continuity, I tested the Bat lead from alternator to isolator and this also checks ok for continuity. All other wiring is intact. I removed the bat wire from the isolator and jumped it through volt meter to ground to determine if there was any voltage coming through it. There is a very small reading when I do this. (Engine running and meter is set to 12v dc when I did this) I would have thought I would see at least 12v dc as this is a direct feed from the alternator. I do not see any type of ground wiring from the alternator to check on. I believe any grounding must happen through the case of the alternator direct to engine and chassis?? I am really stumped at this point. Any thoughts?
PS. The wiring diagram was a great help in determining the wiring as is appears to be correct and no one has bastardized it at this point.
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DanD
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Oct 26, 2006, 2:08 PM
Post #7 of 8
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Re: 1988 GMC P (motorhome) Chassis electrical
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You can’t use a voltmeter as a jumper; you will not have a connection for current to flow.
If you have an ammeter that’s what you want to use to connect to a circuit (in series) and still have continuity. As long as the ammeter has the capacity to handle the current flow of the circuit, in this case the alternators supposed out put.
Voltmeters are connected in parallel and are designed to not take away or add to a circuit, just tell you the available voltage in the circuit.
Here’s how I would connect the meters to give me current flow (amperage) and voltage readings.
Dan.
Canadian "EH"
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Dennicorco
Novice
Oct 27, 2006, 8:34 AM
Post #8 of 8
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Re: 1988 GMC P (motorhome) Chassis electrical
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Dan, EH?, Thanks for all the info. I started cleaning grounds for the batteries and noticed an extrememly loose alt belt. I tightened the belt, cleaned the ground for the chassis battery and now I have what appears to be 13 or better volts reading on the dash guage. Nnot certain what fixed this but runnung fine at this time. thanks for helping me make this a success!!!!
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