Given that you're just checking resistance, I rather doubt that the ignition switch has to be touched or the engine running.

Ignition off for all resistance checks. Only need to be on when checking the 12v from the fuse.

A pot is a 3 terminal device that has a strip of resistance material and a "wiper" terminal that moves along the material (usually carbon) as the pot is moved. So if the pot has a total resistance ot 5k ohms you would read the 5k value when the meter is connected to the two end terminals. when you connect to the wiper and one of the end terminals to the meter the resistance varies in porportion to the position of the wiper. If the wiper was in the middle then the resistance would be 2.5k. If it was 10% from the end it would read 500 ohms etc.The end to end measurement will be constant resistance. It should be in the 3-5 k range. It dosent really matter as long as you see something close. As the wiper moves the resistance changes. If the resistance material is worn out then the resistance jumps all over the place. Generally to an open circuit condition. SO as you move the pot observe the resistance and be sure it progresses smoothly. If not, the pot might be dirty or maybe worn out.

In all cases moving the throttle position the end to end resistance reading should remain constant and the other two should vary. Inversly to each other by the way. One of the resistance measurements will be low when the throtte is closed. and the other will be high. Then when the throttle is opened the reverse should will be true.

So if you see these resistance readings behave in this way we can call the pot portion of the actuator good. There is a motor and a clutch that can be tested as well.

13 is the wiper terminal and 9 & 14 are the end terminals of the pot.

I used to be able to post rather large photos. Its been a while but now it seems I am restricted to really small images. Whats up with that?

Chuck will having a schematic do you any good?

Dave, before you go to the trouble to send the schematic let me try the resistance tests. What you said about the pot makes perfect sense, I was actually inferring most of it from your earlier post, I just wanted to clarify how to vary the pot-and throttle it is. I should have time tomorrow or this weekend and will come back with my findings.
Thank you again.
Chuck.

Dave, do you know the modifications to the switch and actuator tests for a 603 diesel? I'll dig through braingears to see what I can find re the actuator, but I ran your switch tests assuming they lined up. On, Decel, and Accel passed fine. The 1->8 resume test shows a closed circuit in all switch positions - should I be testing a different pin set?

faspakr you are good. OOPS I mis-read the fuzzy MB published schematic. It is not pin 8 but should be pin 6. That probably explains the bad readings. I corrected the earlier post.

OK Dave, are you ready? As near as I can tell, the switch is ok. Pins 1-3 was 0 when on and around 1000 when off. 1-6 was 0 in resume and high otherwise and the same when checking the decel and accel positions. The problem seems to be in the actuator. 9-14 read 600,9-13 was 3 ohms but didn't vary with throttle position, 13-14 was 600 and didn't vary either and 7-10 was 7 ohms. I did have battery voltage at pin 1.
From there, I removed the breather and can't for the life of me locate the actuator! I identified the throttle pull cable, the trans kickdown cable, the throttle plate opening linkage and some other convoluted linkages but nothing looked like it could be an actuator. There was a small block with a plug-in connection that had a little roller and switch on it that followed the linkage and operated the switch but it appeared to be just an open-shut switch. Point me in the right direction, please and thank you again for your time.
Chuck.

I have never had to deal with the actuator in my 124. It should be under the intake manifold somewhere. Its a big thing. About the size of a very large grapefruit. Aluminum housing, with a motor case sticking out of one end. Look one up here on this site you will find a picture of what it looks like. It has to be connected to the throttle linkage somehow. Check both sides of the throtle body. The pedal linkage may come in on one side and the actuator might be connected to the other. Move the throttle linkage an look for anything that moves. Ill pop my hood later this afternoon and have a look myself.

It sounds like there is no mechanical connection to it since the resistance readings did not change. That might be the problem. It might not be electrical in nature at all. How did your cruise control fail? Did it ever work? Shed some light on the history of the cruise control.

Maybe somebody who knows exactly where the thing is located could chime in.

Hey Dave, that's the only thing I could come up with. There is a link that hooks to something under the intake manifold that is probably about that size but I couldn't get a look at it from above. I did look at a parts for sale site and got a picture (and a price - ouch!)but couldn't see anything like it so it's either under the intake or it's not there at all. I'll have to get under the car to check it out. I guess it could also be that it has come unplugged or the wires are broken?
The cruise hasn't worked at all since I bought the car about 11 months ago. Not one glimmer of life from it. Well, I'm off to find a lift. Thanks again.
Chuck.

Booyah! Went to Lowes and grabbed a 25w iron (my 40w was too powerful as well as too physically big to work with on this job) and resoldered every joint. After reinstallation, the system works like a charm. Unbelievable! Thanks to all for the help.

Good job pakr! I just mailed mine off to Dave for a resolder. Guess I coulda tried it meself. Oh well, if he can fix it up I'll be quite satisfied.

Well, I was able to get the car up on the curb and get under it and sure enough, the actuator is buried in the bowels of the engine compartment with the motor mount, starter and everything else in the way. I was able to trace the wire and determine that it was plugged in and the linkage on the actuator is connected. So, that leaves the actuator itself that's probably bad. And, from the looks of it, it will be like putting panty hose on a bobcat in a thunderstorm to extricate it and even worse to install the replacement. So, I may check with an indy mechanic or get it on a lift and see if it looks any less daunting. Anyway, thanks to Dave for the coaching and love this forum. Still don't know if the amp is bad......

Good luck to you with that. I just got back from 250 miles of driving and only had one minor hiccup. For some reason, cruise briefly acted like I tapped the brakes. Quick tap of the resume feature and it came right back to speed like nothing had happened.

My experience says that it is the amp 90% of the time. There is a clutch in the actuator which might have to be engaged and that might be why the resistance readings are not changing. I know on my 420's I can read the resistance change right at the actuator plug. I would try the amp since it is easy to get at first.

OK, I'm still having trouble with mine. I'll play with it more this week when I get a chance, but for now it's dead again. Does anybody have a spare (dead) amp they don't need (14 pin)? I'd like a second one to play with, if possible. Thanks!