well its probably not really a mystery to some but heres the thing...I have a rythmic dimming of my headlights, and all of the electrical system really. As with all early 200 series the fuel pump can be heard at idle speed from in the car, I can hear the pump stuttering in time with the headlights. Now the alternator was replaced with a rebuild about a year ago so naturally im reluctant to believe its that. Mabey its the voltage regulator? Please exscuse my ignorance, im not sure if the voltage reg. is part of the alt. or not. could this be the prob?? other possible solutions? tests I could run? thanx for taking the time

One possibility is that the heavy red wire from the B+ terminal of the alternator to the + terminal of the battery is grounding where it runs under the crankshaft pulley. There is lots of oil, heat, vibration and sharp corners to damage insulation and cause an intermittent ground in this area. When there is a ground, the heavy load on the alternator will cause dimming of everything and a drop in voltage. It is not easy to spot problems here because it is a tight area, but with the belly pan off, you can get a bit of a look from underneath. You could try adding some additional insulation over the wire bundle to eliminate the possibility of the problem being here.

Ross --

That's an interesting suggestion and deserves Matt's immediate attention. It's good you mentioned it. I've seen 4-5 old 240's burn up from that exact short circuit -- it really could be a serious situation. And even if this is not his problem, it's still a good idea to be sure it won't be a problem in the future.

The older 240's, up to about '85 or so, had sharp-edged clips to hold the wire harness down around and under the front pulley. (By '86 Volvo had smartened up and substituted rubberized clips.) These clips would abrade through the insulation, and you had smoke, sparks, flames, and one toasted Volvo.

After cleaning away all the oil, grease, grime, and gunk a good repair is to put the wire bundle into a plastic harness, sometimes called a "wire loom". You can buy this stuff at auto sound shops or perhaps Radio Shack. It's split lengthwise so you can slide it over existing wires for added protection. An alternative is a chunk of hose that is carefully slit lengthwise -- watch your fingers!

if you have a Volt meter with AC capabilities, hook it up at alternator.

If one of the Diodes are out(or starting to leak) you will get

a (AC) reading... it should be close to 0 volts, if you get 1 volt

or more(or it's all over the place) then junk the alternator

and buy a good one

jv

Matt,

A '77 most probably has an external regulator unless the replacement had an internal one, as I was told all replcements will have. If there is a small ceramic plate held in place with two screws at the bottom of the alternator, you have an internal regulator. If there are wires running up to the fender into a metal box, you have an external regulator. Don't be surprised if a rebuilt only lasts a year. My experience with them over the years is that they are not consistant in quality. If you need a replacement you will probably get an internal regulator so just forget about the one on the fender.

Check battery for 12.5 volts with engine off, then perform the following tests:

You can hook up a voltmeter (+) to the B+ terminal (the thick red wire) on the alternator and the (-) to a ground. At idle you should read 13.5 volts (approx.) and should increase with revving of engine about another 1 volt. Adding load like blower motor and headlights should reduce output but revving should increase it again up to about 13.5v. All readings should be steady, if they are alternator and voltage regulator are ok. If the voltage doesn't come back up after load is added the regulator is probably bad. If the voltage fluctuates at idle my guess is that the alternator is bad but see if it fluctuates at a higher voltage also. If it does I don't know what the cause could be. You might want to run the above idle test with the B+ wire disconnected to eliminate the car wiring as a cause.