I just got a 740 turbo ..when I got the car the gas and temp gauges didn't work . I took off the gauges to see if they were all hooked up and they were so I put them back on . Now none of the gauges work . Also the alternater stopped charging my battery .. I've checked all the grounds there All clean . What really gets me is that the battery light in my pannel only comes on when I hit high rpms .. I've checked the alt at kragen and it passed all tests 3 times in a row . So I tested the battery with a multi meter and it reads 12.25v . I also tested it qhen the car was running and it read 13.27v . Later that day I drove it around and then tested it again and while running it tested 11.36v so I revved it up and it slowly started going down intill it hit 9v and it started acting like it was going to die so I jummed in and took off it putted for a min and then started driving fine ....so I tested it again and it was at 11v and going down !!! What could be wrong ?? Could a wire be shorting it out ??

 

Plaese help I don't wanna junk this car

 

Have you checked the alternator output?

 

About the gauges:

It sounds like something is not plugged in right. There is a ground point near the middle of the gauge cluster in the back that is a spade. Make sure that is connected. Also, the large connectors that connect the harnesses to the cluster can be put on improperly if there is no blue clip thing around it to make sure that it's not shifter to the right or left. On my car it had one out of three of these clips. I found the other clips on other gauge clusters that I acquired over the years, so now I have them all. In the attached pictures you can see the blue clip and one connector without one. For ones without, you need to check and make sure that it feel like is is plugged in the middle.

As for the alt, I agree with swift, get it tested. A lot of parts places do it for free.

 

I'm sorry I forgot to mention that I took the cables off the batt when it was running and it died .. Kinda around the same time it started messin up ...but I tested the alt 3 times in a row and it passed all of them including the voltage regulator text . What I have figured out is that when I started my car this morning I tested the batt it read a little over 12v ..but as the car was idleing it slowly went all the way down to about 9v . At that time I reved the motor really highand tested it and it read a little over 13v.... So I am getting charge I think , it's just something that's draining my batt or it's whatever tells my alt to start charging ... Another thing is that when I start the car the only dummy light that comes on is the seat belt one and when I hit high rpms my batt light comes on ...why is that when I just tested that high rpms are what making the alt kick in ??

And with the gauges , I went to pick and pull and found the same car as mine it looked brand new . I took out the gauges an noticed that it's the same as mine but has different color wires ... On mine I have 2 yellow wires going to the prongs and two other wires going to the other set of prongs one white and red and one just white ... While the car I found had one yellow wire on one set of prongs and one white wire on the other set .. Oh and I did forget to mention that we took the wires off the instrument cluster while the batt was still hooked up . I don't know if that makes a difference

 

And I wasn't sure how to check the alt output ... How do you do that ??

 

Ahh...I remember the days of carburetored vehicles...back when you could disconnect the battery leads to see if the alternator was charging...without toasting the electronics...Major, major no-no to do that ...might not have hurt anything, on the other hand it could very well have toasted your amm, ecu, icu, LBJ and JFK!!
It's important to understand that the battery and alternator have a synergistic existence. When one is bad it can easily destroy the other...much as my ex-wife; when one is bad and replaced with a new one, the remaining bad one can destroy the new one. For instance, installing a new battery when the alternator is shot will lead shortly to a discharged battery or, occasionally, an exploded battery if the regulator is charging high enough. Likewise, if a new alternator is installed with a flat or bad battery, the alternator can burn up in no time. Alternators were never designed to chage stone-flat batteries but rather to top them off...keep them charged. Today's 12V auto batteries generally read 12.5V off the shelf. To overcome the resistance of the battery, the alternator must output appreciably more than the 12.5V or it will be a stalemate. I like to see alternator output on rwd Volvos to be in the 13.5 to 14.5V range at idle w/ accessories off...the high side of that range is preferable...to me.
Checking alternator voltage out put is as simple as using the digital volt meter, + to the red big lead on back of alternator and - to chassis ground. I'd worry about your instrument cluster a bit later and work on the charging "cluster" first. If you could locate even the vaguest of repair manuals such as a Haynes...it will have a good section on trouble shooting your charging system and how to calculate drop off voltage. It may be as simple as dirty, loose corroded grounds or as convoluted as dead/ dying battery and/or alternator and/or shorted AMM and/or ecu and or..........

 

I do have a chilton book and it doesn't tell me nothin ...I've checked all the leads all the earthing wires ..I'll check out the output When I get out there pretty soon. .. But what's the acc ?? I know of the ecu but that's the only one out of all of those I know of..:.. But as I said before it is topping off my batt at like 13.72v the problem is not that it's not charging anymore ...it's that when it's idleing when I first start it the batt. Is bein drained intill I rev the engine up really high then it starts charging .... Could it be the computer??is that whT tells the alt to kick in??

 

icu is the ignition control unit I believe it is near the steering column and firewall on 7 series. You need not worry about LBJ or JFK...your car doesn't have them. Not charging when you first fire it up but charges after you blip the throttle to 2 or 3K? That's the excitor circuit of the alternator. Could be a broken wire on back of alternator or bad internals with the alternator. I've driven with that issue for a long time in a car or two. Having a dash mounted volt gauge helps a lot with reducing discharge. I just got in a habit of blipping the throttle so it would begin charging.

 

Yeah that's what I'm doin now and the car hasn't died yet (knock on wood ) .. But I guess I'm gong to just get a new alt when I can afford it ... They want 150 for the one that fits my model so I've been tryin to figure out if it was something else before I buy a new one ...when I have the cash I'll get a new one and let you know if it works .... Intill then thank you for the help ....now all I have to figure out is the gauges .. Fir some reason today my temp gauge started working but when I turned it off and turned it back on it wasn't working .... I also noticed that all the dummy lights stopped working when I turn on my key ..but when I put on my parking break or when I take one of my tail lights out, the indicator light shows up but very faint .. Like you can only see that it's on if your in the dark ....

 

An thank you again for all the help

 

Try moving the ignition switch ever so lightly when it is running. It may be the electric portion of the switch is worn out. I'm sending you a pm.