I am trying to understand it better, but think I'm starting to get it. 936mV is .936V and that's the voltage drop or loss?

____ correct. Ideally the drop should be zero but in the real world there's flexibility. For a circuit like this on a newer vehicle, 100mv would be acceptable. Considering how much wire run, connectors, switches and age your car has, I'd be ok at 250mv. You're well over that.

If the battery drops to 10.2V while starting, and from my understanding is normal (10.2V is per the battery tester I had hooked up), then it's only barely getting enough at times to activate the solenoid.

____ correct again

Any more drop and it won't activate the solenoid basically. As simple as driving it and underhood heat could cause just enough resistance to make it not have enough to fire it up if it's a wire losing voltage under the hood.


____ bingo! GM starters are known for this. 2 problems, on cold start the engine makes a higher draw on the battery so your available voltage is sketchy. The starter is also very close to the exhaust and gets hot increasing resistance and drop.


The positive battery to the suspect (NSS, positive battery cable on starter, etc) point is the voltage drop test and results?


____ exactly. The same method can be used to test ground side. Just use the ground terminal of the battery. If you want to play with this, then meter between starter housing and battery negative. Either way, start at the load (motor, light whatever it is) and the battery. This tells you which side is the failure.


I can drop the steering column to check the ignition switch. Would I just put the probe in the back of the connector? I am assuming so that way it tries to start and puts a load on the starting circuit.

____ yes. This procedure is called "back probing " You come into the connector from the wire side, keeping the connector connected. Just make sure you get to the actual metal terminal. A paperclip or straight pin can be used in tight spaces. NOTE generally it's frowned on to pierce the insulation on a wire for testing BUT personally I'm ok with it inside a vehicle.


I can test the ammeter next time I tinker with it as well.

____ PO disease might have struck here. I'm assuming the gauge is under the dash so access should be easy.


I believe the wiring goes like this for the car: Battery (main cable) to starter. Battery (smaller wire) to ammeter, ammeter to junction block,

___ oh my, that's alot of extra wire run added in. Remember, all wire has resistance. Longer runs add more resistance . Longer runs should be larger gauge wire to help offset the extra resistance. What gauge wire does this have?

junction block to horn relay, horn relay to bulkhead (have to see which wire that is and verify it by cleaning them to see the colors as the bulkhead is hard to see the wire colors and it is a PITA to get to), bulkhead to fuse box, not sure how wires to the ignition switch run, ignition switch to where the NSS would be for a column shift, harness extension to the console NSS, back through the harness to bulkhead somehow, and to starter solenoid. Obviously the main issue is before the NSS and I'll work my way back to the fuse box as far as I can. Then possibly from junction block to bulkhead. Bulkhead is going to be the hard part for me I think. Sorry for the long part here, but I want to make sure I'm not missing a spot to test and have that route written down in my notes.


____ working backwards from the solenoid is preferred but access to connections is a problem to deal with. Remember, we're still lobbing shells, so it's OK to check points out of order. For example, the junction block and alternator stud should both be easy to reach. Check them for drop from the battery. Consider the wiring diagram like a road map and you're trying to get around a road closed for construction. You get off the road and back on somewhere else.

Other points I was thinking of doing a voltage drop test would be ignition switch, junction block, horn relay, and bulkhead if I can figure that out as to which wire it is. The ones under the hood I'll have to get a helper or try to clip it with test leads and use a camera to monitor the reading upon cranking.

____ you can make or buy extensions for the test leads on your meter. You basically already did with the wire you ran into the car from the solenoid. They don't need to be fancy.


Am I tracking so far? I also now see how voltage (hot and ground set up) can be misleading. Learning something new.

____ I understand that it can be confusing checking voltage when you don't have a positive and a negative. But we're not looking for voltage from positive to negative, we're looking for missing voltage between point A and point B. In this case, we're looking for a missing 936mv.

The wires running to the ammeter appear to be 10ga with a 14ga section of fusible link in each one. The ammeter is on a pod under the dash, so not bad to get to at all. I did trace the wires years ago to see what one was from the battery and what one was to the junction block. They were both red, so I labeled them with a piece of painters tape and marker as in/out. I have some stuff to do almost each day after work this week, so may not be able to test the ammeter wires or under hood ones.

Just thinking ahead on this one because my mind wonders. I could cut out the wiring to the ammeter and just run that to the junction block with a fusible link section in it.

____ this would be the original design. Still wouldn't hurt to test the ammeter wiring. In fact, if they test good (minimal voltage drop, say 100mv or less) then you can use them as a substitute for battery terminal. Might make checking voltage under the dash easier. Basically an extension for your meter leads.


The ammeter would stay in place, but not work. I have a plug in cigarette lighter voltmeter/phone charger to monitor voltage. Would that be the way to go if I get voltage drop isolated to the wiring for the ammeter?


____ many vehicles have neither a voltage gage or ammeter and they work fine. You lighter one should be ok. The gauges have their uses, most folks don't really need them though.

I have 8 photos of the wiring diagram I will upload. Not sure of what ones are the ones you're looking for.

_____ thanks, downloaded and I'll print them later. Just the last set showed underhood wires going to certain locations in the bulkhead connector that don't have corresponding wires in the under dash connector. Like they may be from different cars or years.

MI, you mentioned having different diagrams. Can you post them?

I'm thinking the ones you provided so far don't match. I can't follow battery power into the car, the underhood wires go to blank locations in the underdash diagram

RR to you for staying with this, I stepped out as one does not need OPINIONS when trying to resolve a problem. You have good a handle on it so that is all that is needed to help him.
I have seen too many conflicting EXPERT opinions on forums and at car shows that do nothing but have the guy chasing his tail. KUDOS to you sir

One set of diagrams is from a chassis service manual and one is an assembly manual. I will try to see if I missed a page. I did find a picture someone posted online of the red wire that supposedly feeds the fuse block. If it is, I have a new spot to test for voltage drop. Good idea on the ammeter staying hooked up if no drop.

Those are getting to be big numbers, there's clearly a restriction to current flow through the ammeter circuit. 500mv is huge.

That right there accounts for more than half of the previously measured 936mv drop to the solenoid.

I'd bet you could feel the ammeter wires getting warm if you hold them while cranking. That heat explains why the readings go up a bit the longer you crank.

Get those wires out of the loop. Go back to the factory design of battery positive to junction block.

As for decoding the diagram, the letters are color codes of the insulation. The numbers are wire gauge. Note, there's a fusible link in the wire from battery to junction. IIRC, the wire is 10 and the link is 14. If the wire and link used for the ammeter are the correct gauge, you can use them for raw material. Also, good crimping and clean connections are a must.

Fix this and retest the drop to the solenoid.

Sounds like there may be another culprit elsewhere but you gotta fix this first.

After I did the testing for the ammeter I was like "wow". I would have never understood the numbers before, but with kind of getting the theory behind it, those numbers weren't good.

____ to clarify, the ideal voltage drop is zero. But that's an impossible dream, even mega dollar superconductors can't achieve that. In the real world, 100mv through a complete circuit is acceptable. 100mv on either half of a circuit gets sketchy, that's 200mv for the whole circuit. Over 250mv for a whole circuit needs attention.

My initial thought was to cut the wire going to the ammeter and put it right to the junction block making sure there's a fusible link on the wire.

____ duplicates the factory design

Leaving the remaining wiring there just for now but tucking the ammeter to junction block in the wire loom. Later on I can pull it all out.

____ as long as nothing can short, this is ok.

With no power to it, shouldn't be any harm. But didn't want to cut and run new wires if I jumped the gun. The drop at the junction block looks to be after the ammeter output and before the junction block if I'm grabbing the concept.


____ yes you're catching on. There's definitely a problem between the ammeter and the junction, either undersize wire, bad connection or? But, voltage drop is cumulative. You measured about 250mv between battery and ammeter, then 500mv from battery to junction. That means you have 250mv on both sides of the ammeter. You can check this by putting the meter leads on the ammeter and junction block. 250 plus 250 equal 500. As you get more comfortable with this you'll find that not every test needs to be from the battery, but you need to know that at least one test point is good. In this case, both wires for the ammeter are no good.

Hopefully I can get to it Monday after work. Ammeter itself will remain in place (without being hooked up) and be lit up because it's a 3 pod set up under the dash and figure just leave it for now. May try something with it later. I am now wondering if the previous owner or whoever hooked up the ammeter started having issues soon after that?

____ the phrase PO disease applies here. I wouldn't be surprised if they blew the fuse link between the battery and junction, then added the ammeter as part of the repair.

The pigtail that was from the positive that ran to the ammeter was cut and I added a 14ga fusible link section to the junction block. I put some heat shrink tube over the butt splice connector and the ring connector for some protection. I do have the light on the pod still, which is good for looks. The ammeter wire ends were shrink tubed so there are no exposed ends and put back in the loom until I can get them out when I have more time. I did not remove them from the ammeter inside yet, but the test light shows no power to them. I did check it just to make sure some freak thing wasn't going on there.

____ are both ammeter wires disconnected under the hood? If so you should be fine.


Next step, when I get time, is to do a voltage drop test at the junction block wires and the solenoid. I'll compare those numbers and post back when I get those done.


____ please do. This repair should take out half of your solenoid voltage drop.

I am guessing the previous owner did as you said and added the bypass because the wires were junk. I'll inspect the wires for any damage when I get them out. Even if there is a slight voltage drop by eliminating the ammeter wires, it may have enough to fire it up every time now. At least I'm hoping. I'll keep monitoring the voltage at the solenoid as I have been.

____ it may well be enough to get reliable cranking. But, you're this far already, why not keep investigating.


Side note, how do you tell if the fusible link is burned up? I am assuming check voltage at battery terminals and compare to negative terminal to junction block?

____ fue links have wire with a low melting point and insulation with a high melting point. If overloaded, the wire melts away inside the insulation. The melted wire stops conducting electricity but the insulation stays in place. You can measure for an open circuit but it's often faster to give the link a tug. If it stretches, the wire is gone.