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m25-xp instrument panel red and green lamps?

phildogginit

Member II
The instrument panel for the original m25-xp on my e34-2 has red and green lamps. I have never seen them illuminate. The bulbs may be burnt. I have not traced the wires yet.

Anyone know what they are for?

Attached is a photo.

Phil

engine-panel.jpg
 

HerbertFriedman

Member III
My '87 E34 has the same instrument panel but the voltmeter is a replacement for the original ammeter and I have no red and green lamps. They also appear to be added since I cannot imagine anyone putting lamps in the middle of the Universal logo.
 

Christian Williams

E381 - Los Angeles
Senior Moderator
Blogs Author
You need to see where the wires on the back go. They're probably alarm buzzer/lamps for oil pressure, engine temp etc.
1608526766575.png
 

HerbertFriedman

Member III
Phil, I replaced my old, original ammeter with a new one which has a remote shunt. Recall that an ammeter has an internal low resistance shunt and the meter then measures the voltage across this shunt. I did not like the idea of carrying all that alternator charging current all the way back to the ammeter (with internal shunt) at the instrument panel and then back to the engine compartment especially using that "trailer hitch" connector. So I managed to find an ammeter with a remote shunt. I put the shunt in the engine compartment and then ran two (low current) wires back to the ammeter in the instrument panel.

Just to complete the "belt and suspender" approach, I did mount a volt meter (measuring the alternator voltage) in the aft cabin right next to the hour meter for the engine. There was no room for the volt meter on the instrument panel but it is easy enough to go below to view the voltmeter if you suspect a problem. I do understand the the voltage measurement is useful but I do like to see the actual charging current.

The ammeter with remote shunt is not without its own problems, however. One , it was difficult to find and two, the resistance of the two low current wires is "tuned" to the ammeter specs so you need to run those two wires of a certain gauge and length to get the correct ammeter reading. This process is all spelled out in the ammeter instructions This is a bit of a pain. But you can easily check the calibration by measureing the ammeter current directly with a clamp on ammeter by clamping the meter around the heavy wire from the alternator.
 
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