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B+ terminal repair - main fuse box

Help, Advice and DIY Tutorials on Volvo's extremely popular car line -- Volvo's 1990s "bread and butter" cars -- powered by the ubiquitous and durable Volvo inline 5-cylinder engine.

1992 - 1997 850, 850 R, 850 T5-R, 850 T5, 850 GLT
1997 - 2000 S70, S70 AWD
1997 - 2000 V70, V70 AWD
1997 - 2000 V70-XC
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DGM
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Volvo Repair Database B+ terminal repair - main fuse box

Post by DGM » Wed Dec 29, 2010 9:25 am

I am a new member on Matthew’s Volvo site. I would like to share a repair I made recently. This is my contribution for being new on this forum.


S70 1998


Symptoms

Headlights intensity lower when rear defroster is used or when ABS activates. Lights are dimming in dash pod when electrical system is stressed. ECC unit lights flashes after car is started in freezing condition. Starter motor turns normally and alternator is charging well.


Cause


B+ terminal has become resistive under main fuse box.


There is a voltage drop of .5 volt or more between the battery B+ terminal and main fuse box. This is measured under load, blower fan to maximum, rear defroster on, heated seats on with engine idling.


Find photos showing repair and sequences of events;



1- Main fuse box under hood

Image


2- Cable feed from battery to main fuse box

Image

3- Cable terminal under fuse box cover

Image

4- Lost of .5 Volt. All the vehicle electrical current goes through this terminal (except for main starter feed).

Image

5- Under hood undress for repair

Image

6- It shows the overheated terminal at main fuse box. It is resistive and heats under load

Image

7- Terminal end cleaned up with flux paste and soldered instead of being only crimped. Heat shrink installed to improve insulation

Image

8- Drilling location for an additional cable to improve robustness

Image

9- 6 AWG cable (fine wires) with grommet

Image

10- Repair is ongoing

Image

11- Crimped & soldered terminal for the main fuse box

Image


12- Installed cable to reinforce the original circuit

Image

13- Protective tubing under the air-box filter

Image

14- Engine compartment back to normal

Image

15- New reading of 50 milivolts with the same load as before

Image

16- Heat test under load. The connexion is cold.

Image

17- Drill bit of 7/16 " for the hole

Image

18- Terminals

Image

19- Crimping tool for terminals / borrowed to a friend

Image

20- The other half who is claiming her vehicle back. Note the sparkling eyes of car and owner :D which indicates an electrical system in shape.

Image

You would need about 42" of 6 AWG cable of good quality (fine wires). A good alternative will be 4X lengths of 14 gauge (fine wires). You will gain in flexibility during the installation in the fuse box. There is very little space.

Terminals;

Napa 784581, 1 X but sold in 10 units per box. Around 4$
Standard BP 303, 1 X for .75 cents

You can find equivalent terminals locally at your AutoParts

The original wiring is an integral part of the car harness , it is hard to remove for repair. The wiring length isn’t sufficient to support the installation of new terminals.

I have decided to repair the existing one and add reinforcement. It costs me little since I already had the cable and protective tubing. Count 2 hours of your time if you have the material and tools.

http://www.powerstream.com/Wire_Size.htm
http://www.allworldauto.com/tsbs/NHTSA_ ... 24059.html

I think we would be surprised of the number of S/V70 on the road having this problem at high millage.

It is a good idea to verify if you have this voltage drop & if the terminal overheats in the main fuse box. This will give you a good indication of the wiring condition.

Since I made the repair, the overall car driveability has improved and everythings is now back to normal. Blower fan comes on strong after start up.

:)
Last edited by DGM on Sun Jan 31, 2016 9:35 am, edited 3 times in total.


V70 2005 2.4i 195,000km, sold
S70 1998 T5 355,000km, sold
960 1994 80,000km, sold
760 1990 Turbo 265,000km, sold

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Re: B+ terminal repair - main fuse box

Post by JRL » Wed Dec 29, 2010 9:38 am

Good write up
I've been telling people for two years now that their B+ cable is probably bad.

HOWEVER...
It's better just to buy the complete cable from Volvo as it's not just the ends that go bad


2000 V70R Black, 144,000 miles Wife's R.
2007 V70 2.5T White/Oak 111,000 MILES. Polestar tune, IPD bars, rear spoiler, dark grey Thors, DWS 06, HU850, sub.

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Re: B+ terminal repair - main fuse box

Post by RyanGLT » Wed Dec 29, 2010 9:52 am

I have been wanting to see someone with pictures of removing the main fuse box from an 850. I tried to when I first bought my wagon and I was unsuccessful. there has to be a trick to it, but I don't know what it is.


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DGM
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Re: B+ terminal repair - main fuse box

Post by DGM » Wed Dec 29, 2010 12:29 pm

RyanGLT wrote:I have been wanting to see someone with pictures of removing the main fuse box from an 850. I tried to when I first bought my wagon and I was unsuccessful. there has to be a trick to it, but I don't know what it is.
I just looked at the wiring diagram of the 850 and it is much different than a S/V70. Many feeds are distributed from the battery to the different circuits (fuses).

On the contrary in the S/V70 arrangement, 4 wires are pulled together to the main fuse box for distribution. Their termination is the weak point because their ends are only crimped on a terminal. This make a weak electrical contact that is proned to heat.

For the fuse box on the 850 i have never found a trick to access it other than from under.


V70 2005 2.4i 195,000km, sold
S70 1998 T5 355,000km, sold
960 1994 80,000km, sold
760 1990 Turbo 265,000km, sold

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Re: B+ terminal repair - main fuse box

Post by DGM » Wed Dec 29, 2010 12:53 pm

JRL wrote: HOWEVER...
It's better just to buy the complete cable from Volvo as it's not just the ends that go bad
I think you are refering to B+ cable between the battery and the starter motor. This one is available as a cable assembly with a preform terminal at the battery post. I find it a better solution than just replacing the terminal as i did a few years ago.

However upon verification with my local Volvo dealer they could not come up with another solution than installing a "service cable" as i did to fix the heated terminal. Originally four wires are wraped together as a single cable to carry the current to the main fuse box. These wires are an integral part of the vehicule harness. Opening the wiring harness to replace them isn't partical. May be someone has or will developt another approach to it. Definitly the B+ terminals are something to watch for on the S/V70 model in my opinion :).


V70 2005 2.4i 195,000km, sold
S70 1998 T5 355,000km, sold
960 1994 80,000km, sold
760 1990 Turbo 265,000km, sold

reds70turbo
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Re: B+ terminal repair - main fuse box

Post by reds70turbo » Wed Dec 29, 2010 7:27 pm

Those pictures gave me a not so friendly flash back. I have done this repair on my own car, only I used the Volvo B+ cable which runs around $60 bucks. I actually ended up with a new alternator, battery, B+ cable, alt. to starter & starter to battery cables and a ground harness. All were Genuine Volvo parts. Goodbye electrical gremins. :lol:


1998 S70 GLT - 183K - full of fun stuff and meticulously maintained!

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Re: B+ terminal repair - main fuse box

Post by JRL » Wed Dec 29, 2010 7:37 pm

DGM wrote:
JRL wrote: HOWEVER...
It's better just to buy the complete cable from Volvo as it's not just the ends that go bad
I think you are refering to B+ cable between the battery and the starter motor. This one is available as a cable assembly with a preform terminal at the battery post. I find it a better solution than just replacing the terminal as i did a few years ago.

However upon verification with my local Volvo dealer they could not come up with another solution than installing a "service cable" as i did to fix the heated terminal. Originally four wires are wraped together as a single cable to carry the current to the main fuse box. These wires are an integral part of the vehicule harness. Opening the wiring harness to replace them isn't partical. May be someone has or will developt another approach to it. Definitly the B+ terminals are something to watch for on the S/V70 model in my opinion :).
No, that's the starter cable.
I never had to replace a bad cable in an 850, just 99 and 2000 70 series. (1998 B+ cables are usually OK for whatever reason)
The B+ is what goes to the fuse box and is considered to be part of the car's wiring harness and it usually covered under extended warranties


2000 V70R Black, 144,000 miles Wife's R.
2007 V70 2.5T White/Oak 111,000 MILES. Polestar tune, IPD bars, rear spoiler, dark grey Thors, DWS 06, HU850, sub.

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Re: B+ terminal repair - main fuse box

Post by matthew1 » Fri Jan 28, 2011 1:18 pm

DGM, great writeup. I put it in the Repair Database and made your account MVS Contributor status.


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DGM
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Re: B+ terminal repair - main fuse box

Post by DGM » Fri Jan 28, 2011 7:46 pm

Thanks it is appreciated.
Last edited by DGM on Sat Jan 29, 2011 5:48 am, edited 1 time in total.


V70 2005 2.4i 195,000km, sold
S70 1998 T5 355,000km, sold
960 1994 80,000km, sold
760 1990 Turbo 265,000km, sold

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Re: B+ terminal repair - main fuse box

Post by cn90 » Sat Jan 29, 2011 5:34 am

Thank you for the nice DIY!

This gives me incentive to inspect the Main Fuse Box wiring once in a while.

My comment: if you run an additional cable (keeping the original multi-wire cable as shown in Step #6), then I do not think you need a 6G cable, maybe 10G is good enough, just a guess.

The other option is to get rid of all those multi-wire cables (in Step #6), and replace with the single 6G cable as you mentioned.


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2005 XC90 2.5T 110K+

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