'94 850: battery drain, elec, issues MVSOLVED battery cable Topic is solved

sethhahn · Post by **sethhahn** » 30 Aug 2014, 02:25

Sometimes while driving, the radio will shut off and some of the lights in the dash will come on (ABS, SRS etc.)
Usually these lights will blink off and the radio will come back, but sometimes, if this goes on for a few minutes, the car will lose power and die. It will run again after jump starting. During the dash-lights-on state, I've clicked on the dome light to check for power, and the lights are very dim. So I'm thinking that I have a battery/charging problem.
I replaced the battery first, and then alternator last weekend. The new alternator seems to have helped, but the problem surfaced again briefly while driving a few days later.
What the heck is going on??? Is there a fault in the charging circuit?? Or a dying/overheating computer???

Post by **timmybdaddyof3** » 30 Aug 2014, 04:21

I am not totally familiar with volvo's electrical layout, but i would start by checking all of your wiring between the battery and the alternator with a multi-meter....i am willing to bet that somewhere in the chain is a wire with a little too much resistance; as it heats up (either from driving or just electrical load passing through it) the amount of resistance increases and the voltage starts dropping off. As well as testing for resistance, look for any corrosion or connections that are not solid. Another thing to look at is after the car has been sitting (engine compartment cold) start it up and measure voltage at the battery with all the accessories off....drive it around till its up to temp with the electrical system loaded (ac on, headlights, etc), turn off the accessories (but leave the engine running) and check voltage again, shut down the motor and close the hood (to create heat soak), wait 15 mins and check yet again.
All three checks should be within .5v of each other...if it drops more than that there is either a component or wiring issue (duh...but if we can identify the drop point we can start narrowing down components)
let me know your findings

Post by **rspi** » 30 Aug 2014, 04:39

Starting or charging issues, may be a bad battery connection. Common problem with these cars. I went throuvh the same thing.

Post by **timmybdaddyof3** » 30 Aug 2014, 04:56

he listed both the battery and alternator as being replaced....i am assuming that the alternator also contains the regulator but i do not know this for a fact, and am too lazy too look it up at 4 am

Post by **jreed** » 30 Aug 2014, 06:12

I agree with Timmyb's advice: check for voltage drops from the positive battery terminal to the starter and from starter to alternator. One additional possibility is an intermittently bad electrical portion of the ignition switch.

Post by **xHeart** » 30 Aug 2014, 06:29

After battery and alternator, Ignition switch is another trouble spot.

sethhahn · Post by **sethhahn** » 01 Sep 2014, 23:39

Problem solved!!
Thank you gentlemen for your advice!
I checked voltage across test points as suggested. There was a voltage drop on the cable between the starter and the positive battery terminal (during idle) that ranged from 0.6 - 1.6 volts.
I used an IR thermometer to measure temps at all points. The temperature increased at each point on the positive cable as I moved closer from the starter toward the battery. Positive terminal was as high as 150 degF with all major electrical loads turned on, versus 100 degF on the negative battery terminal.
The culprit was a poor post terminal crimp on the positive cable, which also heated up and oxidized the copper down the next few inches of cable.
I cut off a few inches, used dielectric grease and crimped on a new brass post terminal.
Test results after the replacement: 0 voltage drop, 0 difference in temp between positive and negative battery posts.
Thank you!!

Post by **abscate** » 02 Sep 2014, 03:47

Thanks for the report and nice diagnostic tool use!!

Post by **BEJinFbk** » 02 Sep 2014, 08:25

Great example of tracking and solving a voltage drop issue.
Thanks for posting back and closing the loop !

Post by **timmybdaddyof3** » 02 Sep 2014, 08:36

Glad to hear it was that simple.....goes to prove a little knowledge can go a long way.....now for the big question...
How long and how much would a dealer have taken to figure this out?
I am always amazed at the number of "mechanics" who have no comprehension of electrical theory.