MGB: Ignition switch problems

I recently rebuilt the engine in my 1976 NA MGB and I can't get it to start. I have fuel (removed the air filters on dual SU carbs, noted fuel in the venturi), had a spark (removed spark plug from head, grounded and noted spark) and I thought I set the static timing correctly to about 10 degrees BTDC.

I have installed a Pertronix distributor and tested the coil.

When re-checking the static timing, I could not get any spark (as viewed with an inline light to to the #1 Cylinder). There is no voltage to the coil except when the starter is engaged. I tracked the lack of voltage to the white wire on the ignition switch. Only the brown wire (power) and the white/light green wire (radio) wires were energized in the I and II key positions. I should note that I do not currently have the tachometer installed.

My question is this - should I replace the ignition switch, or would it be feasible/advisable to wire one or several separate, two-position toggle switch(es) to bypass this apparent failure of the ignition switch.

Secondly, might a spark be too weak to ignite the mixture if the coil is not powered by both the white/light green wire (from the starter) and the wire from the ignition relay? Or can any one suggest what I'm not thinking of and why the engine won't start? Much thanks.

If you have power going in (brown wire) to the switch and no power going out (white wire) of the switch when the switch is in the on/run position, then I would say the switch has failed internal contacts. The ignition switch is generally not repairable. It takes about half an hour to replace.

The other day I had my tach out... did some work and wanted to test the engine. It would not start with the tach out. I hooked up the tach and away it went.
Try that.

Never ever discount Kimberly as she is never yet wrong.
77-80 switches seem to be tweeky compared to earlier ones; cars try to start while you are driving, start while parked, etc.
Yours may be in there depending on build date.
Regardless, don't mess up the wiring scheme by installing a bunch of patches; either fix what you have or install new. Your heirs will appreciate it.

Thanks for all the advice. I think I'll get a new switch.

I would try bypasing the switch before replacing it. Verify that it is the problem before spending money. Also did you do any rewiring before this?

Good luck,

Paul.

I would try bypasing the switch before replacing it. It isn't very hard to hot wire these cars. Verify that it is the problem before spending money. Also did you do any rewiring before this? If so check, recheck, and then double check that again. Did the car run OK before you did the new dizzy?

Good luck,

Paul.

After seeing that a new ignition switch is 70$ from moss, I did think about bypassing the switch as a troubleshooting step before getting a new switch. I replaced the dizzy as one of the final steps in a complete engine rebuild, so you could say that the engine ran before I replaced it - barely, with excessive blow-by and venting a quart of oil every 50 miles or so, but still ran.

The previous distributor had an external electronic ignition - allison or piranna or something like that - that I removed and replaced with the new distributor. As far as I can tell, the issue is not (yet) in the distributor, as I am not getting any voltage to the coil with the key in the II (ignition - on, starter - off) position, and I do get both voltage to the coil and a spark with the key in the III (ignition - on/starter - on) position. I just don't get combustion.

xof Wrote:

The cowl is currently off, and the lack of voltage in the II position is measured from the leads on the ignition coil. So, I am certain that the ignition switch is bad.

I did think about bridging the white/green radio/accessory wire (which is receiving voltage) to the white ignition wire, but this would be at best a temporary fix, as I would most likely burn up the coil if were to park with the engine off and, say, the lights on, which you noted.

I had decided to replace the ignition switch, but then reconsidered. Being able to control electrical components individually has a certain amount of appeal - motoring the starter until I see some oil pressure, then activating the ignition switch, for instance. Chalk that weird preference up to my aviation background; if it were up to me, I'd have push to reset circuit breakers inside the cockpit instead of fuses under the bonnet, but I'd rather not fix what's not broken. So, there's the financial consideration, but there are also seperate functional and aesthetic considerations.

xof Wrote:

Also never assume that just becouse there is no power at the coil that there is no power at the switch. Find the 6 way connector that the white connects too and test the voltage there. If none, jumper the brown to white and try starting. If it starts then it is the switch, or the wire to the switch. You can verify that later. If it does not start, then check the power at the tach wire. If power there, run a jumper from the tach/6 way directly to the coil.

Anyway around it make completly sure that the switch is bad before replacing it. Your banker will thank me.

Paul

Thanks, all. The ignition switch was definitely the culprit. Just put in 1 momentary DPDT switch for the starter and 3 SPST (ON/OFF) toggle switches (ignition, radio, and anti-run-on) on the dash just to the right of the gauges. Total cost - 10$. Not original, I know, and future owners will no doubt curse me years from now, but I think it's reliable, ergonomic, and that it'll look good, especially when I finish the lacquered mahogany dash and replace all the gauges with ones that work. On to the next project.

Collin