Hi There,

This is my first post so go easy on me!

I have a 1990 volvo 740 turbo - recently my speedometer and odometer died. I found a replacement from a 1989 740 from a guy on craigslist for $20 - While at this guys house I was hoping to pop the old one out and the new one in but of course it wasn't that simple - so I drove home instrument cluster -less (about 45 mins + 20 mins in stop and go traffic).

At this point the car died and engine would not crank. I got a quick jump start and kept the car going all the way to O'Reilly - where they told me the battery is good, but the voltage was a little low on the alternator which could mean its on its way out.

My question is: are there any circuits in the instrument cluster that could have caused this, or am I safe to troubleshoot this issue from the alternator alone?

 

the instrument panel has the alternator light, which is connected to the alternator D+ circuit and without which the alternator won't run, as D+ provides the alternator field coil with its 'bootstrap' current.

 

In layman's terms - your alternator will not charge unless the battery light in the cluster is working.

All the time you were driving without your instrument cluster, the battery was not being charged.