Electrical Problems - Starter Coil & Ammeter

[1972RedNeck]

Here's what I have. I've had our '63 C60 in the shop doing some tinkering and wiring it. Today when I went to move it, it wouldn't turn over. I jumped from the power supply to the trigger terminal and it started right up. I figured it would be an easy fix.

Before I start, I will say that the only wiring I have been doing is on the taillights - nothing more.

As I was poking around, I noticed that the ammeter is pegged on discharge whenever the key is on. I slapped my amp clamp on each battery cable and only have a .3 amp draw.

I unplugged the ignition switch and jumped from power (red) to start (purple). I get a good sized spark so there is obviously a draw, but nothing happens. When I jump the wire, I can hear a sound almost like tuning fork or a vibrating spring that fades out in less than a second.

I put a remote starter switch on the starter solenoid and it turns it over just fine. The solenoid draws about 18 amps.

I unplugged the wiring harness at the firewall and jumped from power to start - and it turned over. Plugged it back in and had the same thing as before. Thinking I might have a short, I unplugged the harness at the firewall and jumped the power wires so I only had incoming power. The ammeter still pegged and I had no spark when I jumped from power to start at the ignition switch plug.

I need help.

[1972RedNeck]

I was just doing some thinking - I was welding on some new light boxes and didn't unhook the battery or anything - that could have cooked the ammeter.

[fleetsidelarry]

sounds like the purple wire is shorting somewhere between the switch and the firewall plug. possibly where the ammeter wire runs IF they run parallel at some point. have you unwrapped the wire harness from the switch to see if any are burned?

[VetteVet]

Originally Posted by fleetsidelarry

sounds like the purple wire is shorting somewhere between the switch and the firewall plug. possibly where the ammeter wire runs IF they run parallel at some point. have you unwrapped the wire harness from the switch to see if any are burned?

This would seem to be where the problem is although I doubt that the purple wire is shorted. More likely it is not making a good connection at the key switch or on the starter solenoid.

A .3 amp draw is not much with the key switch on. The question is how much draw is there with the key off? That would not normally peg the ammeter to discharge.

Unplug the firewall plug for the key switch and check the draw.

When you jump from the red power wire on the firewall plug to the purple wire your solenoid should engage and rotate the engine. I see you said that it does. Your are just bypassing the key switch. A small spark would be normal. I would test the purple wire at the key switch plug with a separate wire connected to the starter, where the purple is connected, and jump it to the red power wire in the firewall connector, and then at the key switch connector. You would be by passing the purple wire completely by doing that. I suspect you might have a poor connection somewhere in the purple wire circuit. Possibly at the solenoid itself.

Since you got rotation at the firewall plug and not at the key switch plug, it seems that the problem is in the harness to the key switch plug. It may be in the purple wire or even in the red power wire.

It's also possible that the red power wire does not have full voltage in it so check the source of the red wire for a bad connection.

Here's a diagram for the 64 truck, it should be pretty close.







Here's the cab side with the ammeter.

[1972RedNeck]

I've done some more plugging around - turns out the red power (battery) can't deliver any amperage. I hooked a 100W light up to the wire and the voltage dropped from 12.86 to 4.21.

For the time being, I ran a jumper wire from the battery to the light switch and the troubles went away.

[VetteVet]

Connect the light right to the battery posts and do a voltage drop test and see what the drop is. If it's only a volt or so then do the same thing at the horn relay where the red wire from the battery connects.

The ammeter is wired in series between the battery and the alternator and it should connect at the horn relay and the battery positive post. Anytime there is a load on the battery the ammeter will reflect it by moving to discharge. If it's pegging then that's a pretty good load. The ammeter should move the needle back to the plus side of center if all is well. The second diagram shows the wiring path for the ammeter with the red wires which are actually black and black with a white stripe.

Since you can jump the solenoid and the engine turns, that indicates that the battery is OK, so the problem is in the control circuit to and from the key switch. This would be the bottom plug in the diagram where the red wire from the relay goes into the cab.

This is the power wire for the whole truck as you can see in the diagram below. The red wire comes into the cab and splits to go to the headlight switch, the fuse panel and the ignition switch. You might have a poor connection on the connector there on the firewall.

You might also unplug the connector for the rear lights and see if the ammeter draw goes away.

Follow the red wire from the bottom left of the diagram and you can see it's path to the key switch, the fuse panel, and the headlight switch.

This diagram is for the charging light dash, not the ammeter but the power wiring is the same.



I hope this give you some help to find the problem. VV

[fleetsidelarry]

well, VetteVet beat me to it. Although it's not a big deal, the diagram for the 60 series (C and L models) in the shop manual for '63 trucks shows 2 red wires from the horn relay running to the firewall plug. one red wire then continues on to the ammeter and another, as he mentioned, goes on to split and supply the fuse panel, the ignition switch and the headlight switch. any connection point in these circuits (at the battery, at the horn relay, at the firewall plug) can be a problem site as VetteVet already mentioned

I know you have it working now, but if you want, you can still try to trace down the problem.

you mentioned that you bypassed the "red" wire with one coming directly from the battery to the light switch. is this correct or did you mean ignition switch? where did you test the current drop? at the ignition switch?