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Oddball electrical experience with my 1990 240 today

Dunno what to make of this. Drove to my first workplace this morning and the car ran like a top per usual.

Got in to drive to workplace #2 and noticed the overdrive light came on on the dash, pushed the button and it went off. Car seemed to run fine but wasn't really paying a lot of attention to it.

Got in to drive to workplace #3 and noticed the OD light came on again. Then I noticed that the "brake failure" light, which has been stuck on for ages even though there's nothing wrong with the brakes, was off. Paying more attention I noticed that the fuel gauge suddenly didn't work. It was bright and sunny so I couldn't tell if the dash lights came on or not when I switched on the headlight, which according to the bumper of the car in front of me worked fine. The hi-beam indicator came on. I noticed that the speedometer no longer worked nor did the trip odometer or the regular odometer. Idle speed was high and the car did not seem to shift into overdrive on the highway.

Got to workplace #3, yanked the fusebox cover and checked all the fuses. They were fine. Noticed that if I turned off the car and restarted, the idiot lights didn't come on at startup, and the OD indicator always came on after the car started. Running very late, had to abandon the examination and go into work.

Came back out four hours later, started the car, everything works normally. Ran like a top all the way home.

WTF?

Reply to
Tim McNamara
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Did you clean the fuses too? They can look fine and still have issues.

Also check the ground strap between the engine and firewall, and the negative battery cable. Bad grounds can cause all sorts of weird stuff.

Reply to
James Sweet

Exactly my thought. I've had several adventures with bad grounds on my

740s and 940s. On both, they split the ground. Part seems to be more for the starting circuit, and the other part seems to affect the dash, and computer, etc. When mine failed, I usually found the ground connected with one last strand of the original cable.

So, James is right, check ALL of the grounds on the car. In fact, go thru and clean at least the most obvious ones.

luck, /glenn

Reply to
/g

WAG, ignition switch? I dunno...

Reply to
clay

I spun all of then in their holders and pulled out #16 for closer examination, since the manual indicated that fuse is involved with a number of these circuits. There was no obvious oxidation or tarnish on the ends of the fuse or the holder contacts.

I'll look at that, thanks!

Reply to
Tim McNamara

Thanks, are there particular places I should be looking (I probably don't have a clue where most of the grounds would be located).

Reply to
Tim McNamara

: > Tim McNamara wrote: : : I spun all of then in their holders and pulled out #16 for closer : examination, since the manual indicated that fuse is involved with a : number of these circuits. There was no obvious oxidation or tarnish on : the ends of the fuse or the holder contacts.

Hi Tim,

Re the fuses, if they are the usual ceramic type with grey end contacts I would remove all of them. Thoroughly clean the fusebox contact strips using fine sand paper, then spray them with electrical contact cleaner and coat them with dielectric grease. Get new ceramic fuses with brass/copper end contacts. My local Volvo dealer did not stock them but an outfit catering to VW's did. Your fuses should then be reliably trouble-free for a long time.

The problem with the original setup is the two dissimilar metals in contact (Copper and Zinc). This can cause "Galvanic action" and the resulting corrosion.

Good Luck. Andy I. ('58 445 "Duett"; '65 122S wagon; '67 121 2-door direct import; '74 145 wagon; '74 142; '86 240 wagon; '93 240 "Classic" wagon; '97

850 AWD wagon)
Reply to
Andy

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