My son and I bought an 87 pickup as a basket case. Head was off. We were assured it had run before. Got the head taken care of and have it back together and it cranks but no spark.

I started looking for power at the igniter and did not see any. I checked further and have no voltage at either side of the fuse marked IGN in the fusebox by the drivers feet (checked with ignition switch on). I replaced the ignition switch and I have power at the connector for the switch - power coming from the harness.

I was testing with my ground lead connected to the negative terminal on the battery so I don't think it is a ground issue.

I am not great with wiring diagrams so the fuse could be a red-herring.

Any ideas for testing and diagnosing would be very welcome!

Rob Crumpley

 

Sounds like a wiring problem going into the fuse box or someone spread the terminals where the fuse plugs in by installing aftermarket stuff giving you a bad connection. What you can do is jump power to the ignition fuse (with a fused jumper wire) and see if the truck starts. Is that the only fuse not getting power? How about the EFI fuse? Does this truck look like it has an aftermarket alarm or kill switch?

 

Thanks for the reply!
The IGN fuse appears to be the only fuse without power. No EFI. The truck and dash area are pretty abused so I do not know about alarm or kill switch. The previous owner did have a big chain bolted to the floor so he could lock up the steering wheel! I will look again for a kill switch.

I will try to set up with a fused jumper to power the IGN fuse line. DO you think it is safe to assume that all the fuse receptacles are wired alike? Meaning if I pull a fuse and find power on the left terminal do you think it is safe to believe that all the fuses should have power on the left terminal?

Again many thanks for thinking about our problem.

Rob C

 

That's a safe bet, the power on one side of the fuse (left or right) is usually that way for all the other fuses. If you are unsure of which side you can always have your meter or test light set at the igniter and then hook up your jumper . If you hook the jumper up wrong then your just be sending power to where power is supposed to be anyways, shouldn't be a problem unless there is a short to ground and that's why you use a fused jumper. Hope this helps.

 

Electrical is not my strongest area. I have seen the back side of the fuse box get some corrosion in there. If you want to check the back side of the fuse box, remove the bottom bolt that holds the fuse box to the body.

Then with your knees on the ground and your right hand, put your thumb on the left side of the fuse box. Your ring finger and pinky will be on the right side of the fuse box. Your middle finger goes on top of the fuse box and slide it down the center until you feel your finger nail slide under a tab. While trying to raise your middle finger/lifting the tab, kind of rock the fuse box off of the flange at the top of the fuse box.

I am not the best with electrical test and 854x4 would be better for that but if you want to do a visual inspection, and I have seen corrosion or even melted fuse boxes in the past where someone probably put in to large of a fuse.

Not the best picture but to give you an idea of what I am talking about. A picture of a possibility and some what of a common problem https://www.yotatech.com/forums/f199...l#post52019346 Scroll down on Corys thread for a picture of similar things I have seen on the back side.

 

Thanks for the help. I used an "Add-a-circuit" to get power to the left side of the IGN fuse slot. (All other fuses appeared to have power on the right.) Still no joy.
I measured power at the igniter by disconnecting the green barrel with 2 wires attached to the igniter. Checked both sides (ie it has 2 wires) no power. I guess I will have to pull the fusebox.
Thanks again - if you have any further ideas please let me know.

Rob C

 

OK I'm looking at a diagram while I type this so hopefully I get it right. You said no EFI so I'm assuming 1987 22R Carb. Looks like power comes from 30amp fuse AM2 under hood to ignition switch, then with the switch ON power goes to the Igniter/Coil and IGN fuse, then from IGN fuse to emission computer and other systems. So the power for the Igniter comes before the IGN fuse, from the ignition switch and that power comes from the 30amp fuse under the hood. Should be a black wire with a red tracer at the igniter. So you need to check the AM2 fuse under hood and start tracing from there. If you jumped power to one side of the fuse looks like you were only sending power to the emission computer and other systems, try jumping the other side (right) of the fuse and that should send power back towards the igniter and ignition switch provided the wiring is intact. On the diagram looks like the two colors used for this wiring are black with red tracer and black with yellow tracer.

 

854x4 is correct.
Igniter takes power directly from Ignition switch, not IGN fuse.
IGN Fuse is a wrong name. It supplies ECU, dash warning lights, Alternator IG (excitation) and reverse lights, but not the IGNITION circuit (DUH!)

With ignition ON, trace the black wire with red stripe and see where you lost power.