The Stovebolt Site Forums The Shop Area The Electrical Bay 12 v coil external resistor

Is the external resistor on a 53 mounted on the fire wall? I get 12 v with the key on there and at the coil. It is my understanding that the other wire to + side of coil gives it a 12 v boost while the starter is engaged to help because the starter draws so heavy. I get 0 v volts at the wire from starter solanoid to coil with just key on so I think I'm right. I have a new 12 v coil no ext. resistor req. laying around. can I bypass the resistor and use it. or I'm I way off base?

well, I'm not sure about bases, but with a 12V system you need either an external ignition resistor or an internally resisted coil, not both - 53 [6V] didn't originally have the resistor so it might be mounted anywhere, later originals were mounted on the firewall .... with the key on you should have power at the resistor, but there will be power at/from the starter to the coil only when the starter is engaged, which allows the coil to get full 12V and produce a fatter spark when cranking

so is there a problem with starting? does your externally resisted coil seem to be causing trouble?

Bill

With the ignition switch on, AND THE POINTS CLOSED, the voltage at the + terminal of the coil should read about 9.5 VDC. The only time you'll see a voltage reduction is while current is flowing through the points. If the points are open, you'll see 12 volts at the coil because no current is flowing. The bypass lead from the starter solenoid to the coil provides full battery voltage while the starter is cranking, which is lower because of the load on the starter. The coil primary is actually wound to operate properly at 9.5 volts or so. If you bypass the resistor the points will burn quickly from too much current flow. The "no resistor required" coil will probably give you a weak spark during cranking because of inadequate current flow while the battery voltage is decreased from powering the starter.
Jerry

Thanks for the info, I just thought may be my spark was a little weak because I'm getting some knock under load and timing does not help. I'm begining to think it maybe in my #6 cylinder but need to borrow a compression gauge from brother in law to check that out next. sounds ok in driveway but I'm afraid I may have bigger problems unless the 235's are that noisy, but I doobt it. Thanks again Scott

Hope it's not that #6, those kind of issues can be a serious pain,...

There are a few internaly resisted coils that fire hot even when cranking. I left the resistor and bypass circut off my bolt in favor of a Bosch Blue coil. It pumps out higher voltage than the stock GM coils, and so far hasn't worn my points any more than normal. Best part is they are affordable and easy to find. Not a GM part for those tryin to keep it as stock as possible, but still has turned out to be a great choice in my case.

Thank for the help so far but I think I need to move this to engine problems but I do not know how.
All of the plugs have spark.However #6 plug is stone cold and clean like it has never seen fuel after running in the driveway. The other 5 where hot and looked used. When I pull the wires one at a time while the truck is running (roughly) plug #'s 1,2,3 cause it to run worse. plug #'s 4,5 & 6 do not seen to affect to running at all. The truck knock bad under load and has serious lack of power. Maybe little to no fuel to the back 3 cylinders, getting none to #6 ??

It sounds like you've got a vacuum leak that is putting nothing but air into #6. Try using a propane torch with a piece of rubber hose on the end of the pipe instead of the burner head. Turn the valve on a little, and run the end of the hose around the head/intake area where the manifold bolts on. If the engine smooths out or picks up speed, you've found the area of the leak. A cracked manifold runner is a possibility, but it's more likely to be a warped manifold that doesn't bolt up to the head correctly. Once you find the leak, get the manifold machined, or change gaskets, etc. to solve the vacuum leak problem.
Jerry

Iemoved valve cover and found the intake pushrod for #6 was out from under the rocker arm. I put it back under and it set it to the lifter cup and stays on while the truck is running, so that was the no fuel to #6 problem. Now new problem is #1- 120#, #2-110#, #3-90#, #4-0#, #5-0#, #6-0#. valves are all moving as they should (I think). So do I need to remove head and look for head gasket, valves, or rings. starting a new post in engine and driveline

Have you adjusted the valves? If the valves on those cyls. are too tight & not letting them close it can cause this. Back the adjustments off on the last 3 cyls. & run the check again. Listen & see if you can hear the compression coming out the exhaust, intake or crankcase.

Thanks for the tips I started a new post in engine & driveline but here is where I'm at so far 235 running rough and knocking under load so I removed the valve cover and found the intake push rod out from under the rocker arm on #6. I was able to put back under and felt like it seated in lifter so ran engine and it looked to be ok. 0 psi of compression in 4,5 & 6. 1,2,3 120# 110# &90#. put air into # 4 spark plug hole and heard it leaking out thru I think exhaust.
removed rocker arm rack and tried again and was getting pressure trying to blow my hose out. removed #5 plug and the air into #4 comes out #5 plug hole so that would explain the air leak through #5 exhaust valve as the air went into #4. #6 seems to have some pressure now so maybe I had the pushrod too tight and it was holding the valve open. Maybe I 'll get lucky and only need a new head gasket and not cracked some where. any thing else I should try before I pull the head ? or what else should I look for? I had this post under 12 v coil before because I thiught it was a spark knock.