when i turn on the ignition in my 76' 300d the battery light goes dim, i have been having glow plug issues so the glow indicator light is not functioning, the battery light will stay dim indefendantly and if i try and turn the motor over all i get is a "click" from one of the relays. when i remove the connector from the glow plug relay the battery light is once again to its full brightness. often i still still get just a "click" after i put the vehicle in park to first to park again, sometimes moving to in neutral i will get her to crank over and start.

is there some ladder logic from the glow plug relay which prevents the starter from being engaged if the glow cycle has not been completed?
or do i just have compound problems arising from a faulty glow plug relay and a bad neutral position switch?

new battery and alternator 1 week old
new starter 2 months old
battery fully charged

 

I think you have 2 problems, bushings worn out or missing on the gear shift linkage rod and a glow relay thats inop or the strip fuse on it is cracked or burnt out.

 

i dont think that the glow circut is computer controlled on that car, so you should be able to get a good diagram of it and wire in your own control switch, and it shouldnt have any ties to starter operation.

you may want to check for a park/neutral safety switch on your transmission, or it also may be right up by the shifter on the center console. if these go bad, the car will think that the tranny is engaged and cut power to the starter. i had one go bad in my 84 sel, but it went bad in the park position only, so i never fixed it and couldnt tell you exactly where it is.

 

Your glow plugs are in series. If one is out, then all are out. Turn on ignition and measure the voltage on the glow plug nearest the firewall. It should read between 10 and 12 volts. If it's zero, either relay is bad, or it's a bad ignition switch... or a blown fuse.
However, if you get a good reading, check the next gp... If it reads zero, then the gp next to the firewall is bad. Change it and check again. You should then read between 10 and 12 volts on all gp's.

 

I have converted my glow plugs to the parallel configuration.

the problem with the dimming battery light only occurred on the last few very very cold days. now that its a tad warmer i'm no longer having that issue. so trouble shooting is difficult at best when i can not recreate the situation at my will.

as far was i know this is the diagnosis of what occurred:

a charging system problem developed due to an unknown, unrepeatable cause to the point where there battery was not charged sufficiently at slow speeds. at higher rpm's the alternator output was enough to cover all of the loads and the battery began to charge.

now on start up the battery was under relatively heavy load due to the current draw of the glow plugs thus exceeding the batterys current output( due to its previously mentioned discharged state) to a level where the starter and the glow plugs could not be operated simultaneously.

now i got her to start by inadvertently turning the ignition on and warming the plugs. once i shifted gears and triggered the switch that eliminates the circuit that turns on the glow relay i achieved two things separately which are normally simultaneous.

the glow plugs still remained hot for a time with the voltage removed allowing the engine to start without the glow relay engaged there by reducing the current draw to an acceptable level.

i'am still going to go through it one more time when i go in for my weekly tinker session.

 

It seems that's a common problem.That is, the alternatoronly charges the battery when driving, preferably at highway speeds. On my 1982 300DT the alternator occassionally needs to be loosened beforetightening theadjusting nut. That has to be done periodically. In fact it's now overdue.

However,you caninstall a different size pully to increase voltage/ampswhen at idle. The other solution is to install a higherampalternator from a later model... Apparently it's a bit tightputting on the belts, and you must also put in heavier wiring to the battery.... But in the end you're left with more than enough voltage/amps...

 

Well, it now seems as if I'm having a simular problem and my alternator belts are tight. Although the battery light never comes on when idling, it only reads 12.45 volts at the battery and 13.50 volts when reved up. I just nowposted the problem at http://www.schumanautomotive.com/for...ead.php?t=2800
under bbbear.... If those guys can't solve it, no one can...

 

i just got everything solved. it was the grounding point on the transmission.

here is a copy of the walk thru what i have posted elsewhere


CHECK your grounds, don't just check them renew them. unbolt the ground from the transmission and get a cordless drill and a wire brush and clean all of the oil and sediment away. Twice. do the same for the connection which attaches to the frame member. also clean up the bolts that fasten them to their individual components.

secondly check to see that the braided copper cable is in good shape and the connections are still solidly soldered in place.

now move up to the battery. check the battery cable connection to the battery post, it must be tight, no wiggle room at all. get out your deep 10mm socket and pull the battery. now to et to the lower grounding point you must remove the battery box. there are two screws fastening the box. one at the 3/4 back and on the passengers side. and another which is accesses from right in front of the radiator.

pull the box and remove the cable. do the same with the rotary wire brush on both sides of the connection point. don't forget any other auxiliary grounds(the 300d has on auxiliary ground there for the fog lights) clean up the bolt and nut on the mating faces/ or replace it. a new cable is inexpensive 4-5 dollars and is well worth it to renew the ground connections.

reassemble. knock as much of the rust, if you have any, from the battery tray and replace it the tray. add an acid neutralizing pad, or a felt pad permeated with baking soda if you have no alternate.reinstall battery.

remember to clean the corrosion off the terminals and also inspect the + positive cable and replace the connection if necessary.

the terminal style where the wire is placed between either side of the clamps and tighten is the least efficient connector. a soldered connection replacement will last a lifetime.

this might not solve all your problems but i'm willing to bet a gallon of Bio that it is the root of many.

check the battery for charge before you reinstall it. a dead battery is really hard on an aging alternator.

try this and come back with your results.

total time one hour